MXPA06009940A - Crystal structure of 3',5'-cyclic nucleotide phosphodiesterase (pde10a) and uses thereof - Google Patents

Abstract

Crystal structure of phosphodiesterase 10A (PDE10A), and the 3-D atomic coordinates of the PDE10A binding domain, as described and used for the identification of ligands, including PDE10A inhibitors, used to treat various psychological disorders.

Description

CRYSTALLINE STRUCTURE OF PHOSPHODIESTERASE OF THE 3Y5'-CYCLIC NUCLEOTIDE (PDE10A) AND USES OF THE SAME FIELD OF THE INVENTION The present invention relates to crystalline compositions of Fosphodiesterase of the 3 ', 5'-Cyclic Nucleotide (PDE10A) of a mammal, method for preparing such compositions, methods for determining the 3-D atomic coordinates of such composition , methods for identifying PDÉ10A ligands that use a structure based on drug design, the use of the 3-D crystal structure to design, modify and evaluate the activity of potential inhibitors, and the use of such inhibitors, for example, as psychotherapists.

BACKGROUND OF THE INVENTION The second messengers of the cyclic nucleotide (cAMP and cGMP) play a central role in the signal transduction and regulation of physiological responses. Their intracellular levels are controlled by the complex superfamily of cyclic nucleotide phosphodiesterase (PDE) enzymes. The PDE superfamily is comprised of metalphosphohydrolases (e.g., g2 + and Zn2 +) that specifically unfold the 3 ', 5'-cyclic phosphate portion of cAMP and / or cGMP to produce the 5'-nucleotide. The sensitivity of physiological processes to cA P / cGMP signals requires that their levels be maintained precisely within a relatively narrow range in order to provide optimal sensitivity in a cell. The PDEs of the cyclic nucleotide provide the major path to eliminate the cyclic nucleotide signal for the cell. PDEs are critical determinants for the modulation of cellular levels of cAMP and / or cGMP by many stimuli. Members of the PDE superfamily differ in tissue distributions, physico-chemical properties, substrate and inhibitor specificities, and regulatory mechanisms. Based on the differences in the main structure of the known PDEs, these have been sub-divided into two major classes, class I and class II. To date, no mammalian PDE has been included in class II. Class I contains the largest number of PDEs and includes all known mammalian PDEs. Each class I PDE contains a conserved segment of ~ 250-300 amino acids in the terminal portion of the carboxyl of the proteins, and this segment has been shown to include the catalytic site of these enzymes. All the known class I PDEs are contained within the cells and vary in the sub-cellular distribution, with some being associated mainly with the particulate fraction of the cytoplasmic fraction of the cell, others being uniformly distributed in both behaviors. PDES from mammalian tissues have been sub-divided into 11 families that are derived from separate gene families. Families are named PDE1, PDE2, PDE3 ... to PDE11. Within each family, there may be isoenzymes such as PDE1A, PDE1B and PDE1C, and PDE10A1 and PDE10A2. PDEs within a given family can differ significantly, but members of each family are functionally related to each other through similarities in amino acid sequences, specificities and affinities for cGMP (PDE5, PDE6 and PDE9) or cAMP (PDE4, PDE7 and PDE8) or the accommodation of both (PDE1, PDE2, PDE3, PDE10 and PDE11), inhibitor specificities and regulatory mechanisms. The comparison of the amino acid sequences of the PDEs suggests that all PDEs can be multidomain chimeric proteins, which possess different domains that provide for catalysis and a number of regulatory functions. The amino acid sequences of all mammalian PDEs identified to date include a highly conservative region of approximately 270 amino acids located in the carboxy terminal half of the proteins. (Charbonneau, et al., Proc. Nati. Acad., Sci. (USA) 83: 9308-9312 (1986)). The conserved domain includes the catalytic site for hydrolysis of cAMP and / or cGMP and two putative metal binding sites (presumably zinc) as well as family-specific determinants. (Beavo, Physiol, Rev. 75: 725-748 (1995); Francis, et al., J. Biol. Chem. 269: 22477-22480 (1994)). The amino terminal region of the various PDEs are highly variable and include other family-specific determinants such as: (i) calmodulin binding sites (PDE1); (I) non-catalytic cGMP binding sites (PDE2, PDE5, PDE6); (iii) membrane targeting sites (PDE4); (iv) hydrophobic membrane association sites (PDE3); and (v) phosphorylation sites for any calmodulin-dependent kinase (II) (PDE1), the cAMP-dependent kinase (PDE1, PDE3, PDE4) or the cGMP-dependent kinase (PDE5) (Beavo, Physiol, Rev. 75: 725-748 (1995); Manganiello, et al., Arch. Biochem. Acta 322: 1-13 (1995); Conti, et al., Physiol, Rev. 75: 723-748 (1995); WO 99/42596 ). Although all known mammalian PDEs are either dimeric or oligomeric, the functional importance of this quaternary structure is not known, and experiments further indicate that in some PDEs the components required to catalyze hydrolysis of the phosphodiester linked in cAMP and cG P are contained in a single catalytic domain and that the interactions between two catalytic domains within a dimer or between the catalytic domain and the regulatory domain are not required for this process. { See Francis, S.H. et al., Prog. Nuc. Acid Res Molec. Biol., 65: 1-52, 2001). PDE10 is identified as a single family within the PDE superfamily based on the primary amino acid sequence and different enzymatic activity. Selection of homology of EST databases has revealed mouse PDE10A as the first member of the PDE10 family of the PDE10 family of phosphodiesterases (Fujishige et al., J. Biol. Chem. 274: 18438-18445, 1999; Lougheny, K. et al., Gene 234-109-117, 1999). The murine homologue has also been cloned (Solderling, S. et al., Eur. J. Biochem 266: 1118-1127, 1999). Mouse PDE10A1 is a 779 amino acid protein that hydrolyzes both cAMP and cGMP aAMP and GMP, respectively. The affinity of PDE10 for cAMP (Km = 0.05 μM) is higher than for cGMP (Km = 3 μM). However, the Vmax of approximately 5-fold for cGMP on cAMP has led to the suggestion that PDE10 is a cGMPase that inhibits cAMP. (Fujishige et al., J. Biol. Chem. 274, 18438-18445, 1999; EP 1250923). The human gene encoding PDE10 has been cloned and found to span more than 200 kb with 24 exons. (Fujishige, K. et al., Eur. J. Biochem., 267, pages 5943-5951 (2000)). PDE10 is located only in mammals relative to other PDE families. It is reported that the mRNA for PDE10 is highly expressed only in the testes and the brain (Fujishige et al., J. Biol. Chem. 274, 18438-18445, 1999, Soderling et al., Proc. Nati. Acad. Sci. (USA) 96, 7071-7078, 1999; Lougheny, K. et al., Gene 234-109-117, 1999). These initial studies indicate that within the brain the expression of PDE10 is higher in the stratum (caudate and nucleus), n. accubens, and the olfactory bulb. More recently, a detailed analysis has been made of the expression pattern of PDE10 mRNA in rodent brain. (Seeger et al., Abst. Soc. Neurosci., 36: 345, 10, 2000). Selective inhibition of PDE10 has been investigated for the treatment of various diseases of the central nervous system. EP 1250923 discloses several specific PDE10 inhibitors with anti-psychotic properties useful in the treatment of disorders including, multiple variants of schizophrenia, anxiety disorders, movement disorders selected from Huntington's disease, Parkinson's disease and dyskinesia, alcohol addictions and drugs, cognitive deficiencies and mood disorders. Several methods have been used in the past and continue to be used to discover selective inhibitors of biomolecular targets such as PDE10. The various methods include the discovery of ligand-directed drugs (LDD), quantitative structure activity ratio analysis (QSAR); and comparative molecular field analysis (CoMFA). The CoMFA is a particular type of QSAR method that uses statistical correlation techniques for the analysis of the quantitative relationship between the biological activity of a set of compound with a specific alignment, and its three-dimensional spherical and electronic properties. Other properties such as the hydrophobicity and hydrogen bond can also be incorporated in the analysis. An invaluable component of these methods of drug discovery is a structure-based design, which is a design strategy for new chemical entities, or the optimization of major compounds identified by other methods that use the three-dimensional (3D) structure of the objective biological macromolecule obtained for example, by NMR studies of nuclear magnetic resonance or X-rays, or from homology models. Analyzing the 3-D structures of proteins provides crucial insights into the behavior and mechanics of drug binding and biological activity. Coupled with computational techniques including model and simulation, the study of biomolecular interactions provides details of events that may be difficult to investigate experimentally in the laboratory, and can help reveal important topological features to determine molecular recognition. As those skilled in the art will recognize, this information can, in turn, be used to predict the complex formation of the ligand receptor, and to design ligand and protein mutations that produce desired ligand receptor interactions. The regulation of PDEs is important to control thousands of physiological functions, including visual response, smooth muscle relaxation, platelet aggregation, fluid homeostasis, immune responses and cardiac contractility. PDEs are critically involved in the feedback control of cAMP and cellular cGMP levels. The PDE superfamily continues to be a major target for pharmacological intervention in a number of medically important conditions, including cardiovascular disease, asthma, depression and male impotence. For example, PDE5, found in varying concentrations in a number of tissues, has been recognized in recent years as an important therapeutic agent (See UK Patent Application 012641 7.5, filed November 2, 2001). For this purpose, the demand for specific and potent PD E inhibitors for use in physiological studies and therapeutic properties continues. In this way, three-dimensional structures (3D) of PDE2, such as PDE 1 0A obtained, for example, by nuclear magnetic resonance or X-ray MR studies or from homology models, and by analyzing the structures using computational methods, are obtained. such efforts are facilitated.

HIS MARIO OF THE INVENTION The present invention provides crystalline compositions of PDE 1 0A, and specifically of the catalytic region of PD E 10A. The invention further provides methods for preparing such compositions, methods for determining the atomic coordinates of 3-D X-rays of such crystalline compositions, methods for using the atomic coordinates together with the computational methods for identifying binding site (s), methods to produce the 3-D structure of PDE10A homologs and methods for identifying ligands which interact with the binding site (s) to agonize or antagonize the biological activity of PDE10A, methods for identifying inhibitors of PDE10A, pharmaceutical compositions of inhibitors, and methods of treating psycho-therapeutic disorders using such pharmaceutical compositions. In a preferred embodiment of the invention, crystalline compositions of the catalytic region of PDE10A are provided. One aspect of the present invention provides methods for crystallizing a PDE10A polypeptide ligand complex comprising a polypeptide. Preferably, in methods for crystallizing a PDE10A polypeptide ligand complex comprising an amino acid sequence spanning amino acids 442 to 774 listed in SEQ. FROM IDENT. NO .: 1, comprising: (a) preparing solutions of the polypeptide, ligand and precipitant; (b) developing a crystal comprising polypeptide molecules from the mixing solution; and (c) separating such a crystal from the solution. The development of the crystallization can be carried out by various techniques known to those skilled in the art, such as, for example, batch crystallization, liquid bridging crystallization or dialysis crystallization. Preferably, the development of crystallization is achieved by using steam diffusion techniques. One embodiment of the present invention provides crystalline compositions of PDE10A comprising a crystalline form of a polypeptide with an amino acid sequence, which encompasses the amino acids Thr442 to Asp774 listed in SEQ. FROM IDENT. NO .: 1, wherein the crystalline composition has a spatial R3 group and unit cell dimensions a = b = 120.56 A, c = 82.23 A. In a second aspect, the present invention provides vectors useful in methods for preparing a catalytic domain Substantially purified C-terminal PDE10A comprising the polypeptide with an amino acid sequence spanning the amino acids Thr442 to Asp774 listed in SEQ. FROM IDENT. NO.:1. In a third aspect, the present invention provides methods for determining the x-ray atomic coordinates of the crystalline compositions at a resolution of 2 A or 1.8 A. In a fourth aspect, the present invention provides a molecular or molecular complex crystal, in where the crystal has atomic coordinates substantially similar to the atomic coordinates listed in FIGURE 1 or portions thereof, or any scalable variations thereof. In a fifth aspect, the present invention provides a molecular crystal or molecular complex, wherein the crystal comprises a polypeptide with an amino acid sequence spanning the amino acids Thr442 to Asp774 listed in SEQ. FROM IDENT. NO .: 1. A further embodiment of the invention provides a crystal comprising an amino acid sequence that is at least 98%, 95% or 90% homologous to a polypeptide with an amino acid sequence spanning amino acids Thr442 to Asp774 listed in SEC. FROM IDENT. NO .: 1. A still further embodiment of the invention provides a crystal comprising an amino acid sequence that is at least 98%, 95% or 90% homologous to a polypeptide, with an amino acid sequence spanning amino acids Thr442 a Asp774 listed in the SEC. FROM IDENT. NO .: 1, and which has the atomic coordinates listed in FIGURE 4. In a sixth aspect, the present invention provides a molecular or molecular complex crystal, wherein the crystal comprises a polypeptide, or a portion thereof, with atomic coordinates that have an average root deviation of squares from the atoms of protein structures (N , Ca, C and O) listed in FIGURE 1 or less than 0.2, 0.5, 0.7, 1.0, 1.2 or 1.5 A. In a seventh aspect, the present invention provides a three-dimensional, translatable, scalable configuration of derived points from structural coordinates of at least a portion of a PDE10A molecule or molecule complex comprising a polypeptide with an amino acid sequence spanning amino acids Thr442 to Asp774 Listed in SEQ. FROM IDENT. NO .: 1. In one embodiment of this aspect, the invention also comprises the structural coordinates of at least a portion of a molecule or molecular complex that is structurally homologous to a molecule of PDE10A or molecular complex. On a molecular scale, the configuration of derived points from a homologous molecule or molecular complex has an average root deviation of squares of less than about 0.2, 0.5, 0.7, 1.0, 1.2 or 1.5 A from the structural coordinates provided in FIGURE 4. In an eighth aspect, the present invention provides a computer to produce a three-dimensional representation of: a. a molecule or molecular complex comprising a polypeptide with an amino acid sequence spanning amino acids Thr442 to Asp774 listed in SEQ. FROM IDENT. NO .: 1, or a counterpart or a variant thereof. b. a molecule or molecular complex, where the atoms of the molecule or molecular complex are represented by the atomic coordinates that are substantially similar to, or are subsets of, the atomic coordinates listed in FIGURE 4; c. a molecule or molecular complex, where the molecule or molecular complex comprises atomic coordinates that have an average root deviation of squares of less than 0.2, 0.5, 0.7, 1.0, 1.2 or even 1.5 A from the atomic coordinates for the atoms of carbon structure listed in FIGURE 1; or d. a molecule or molecular complex, wherein the molecule or molecular complex comprises a cavity or binding site defined by the structure coordinates that are substantially similar to the atomic coordinates listed in FIGURE 4, or a subset thereof, or more preferably the structural coordinates in FIGURE 4, corresponding to one or more PDE10A amino acids, or conservative replacements thereof, in SEC. FROM IDENT. NO .: 1, selected from Leu625, Phe629, Val668, Phe686, Met703, Gln716 and Phe719. wherein the computer comprises: (i) a computer-readable data storage medium comprising a data storage medium encoded with computer-readable data, wherein the data comprises structure coordinates of FIGURE 4, or portions of the same, or substantially similar coordinates thereof; (ii) a functional memory for storing instructions for processing such computer readable data; (iii) a central processing unit coupled to such functional memory and to the computer readable data storage means for processing such computer readable data in three-dimensional representation; and (iv) a screen coupled to the central processing unit for displaying such a representation. The computer configured according to this aspect of the invention can be used to design and identify potential PDE10A ligands or inhibitors, for example, commercially available molecular modeling software in conjunction with the drug design based on the structure as provided herein. In a ninth aspect, the present invention provides methods that involve molecular replacement to obtain structural information about a molecule or molecular complex of unknown structure. In one embodiment, the method includes crystallizing the molecule or molecular complex, generating an X-ray diffraction pattern from the crystallized molecule or the molecular complex, and applying at least a portion of the structure coordinates set forth in FIG. 4 to FIG. X-ray diffraction pattern to generate a three-dimensional electron density map of at least a portion of the molecule or molecular complex. In another embodiment, the present invention provides a method for generating 3-D atomic coordinates of a homologous protein or a variant of PDE10A using the X-ray coordinates of PDE10A described in FIGURE 4, comprising, a. identifying one or more polypeptide sequences homologous to PDE10A; b. aligning such sequences with the sequence of PDE10A ia which comprises a polypeptide with an amino acid sequence spanning amino acids Thr442 to Asp774 listed in SEQ. FROM IDENT. NO .: 1; c. identify structurally conserved and structurally variable regions between such or such homologous sequences and PDE10A; d. generate 3-D coordinates for structurally conserved residues of the homologous sequences from those PDE10A using the coordinates listed in FIGURE 4; and. generate conformations for the loops in the structurally variable regions of the homologous sequence (s); F. construct the side chain conformations for the homologous sequences or sequences; and g. combine the 3-D coordinates of the conserved residues, loops and side chain conformations to generate complete or partial 3-D coordinates for the homologous sequences. The modalities of the ninth aspect provide methods, which also comprise refining and evaluating the partial or total 3-D coordinates. These methods can thus be used to generate three-dimensional structures for proteins for which up to now the three-dimensional atomic coordinates have not been determined. Depending on the degree of sequence homology, the newly generated structure can help to produce enzymatic mechanisms or can be used together with other molecular modeling techniques in the structure based on the drug design. In the tenth aspect, the present invention provides methods for identifying inhibitors, ligands and the like of PDE10A by providing the coordinates of a PDE10A molecule to a computer modeling system; identifying chemical entities that are likely to bind to, or interfere with, the molecule (for example, by selecting a small molecular library); and optionally, procuring or synthesizing and analyzing the compounds or analogues derived therefrom for bioactivity. In certain embodiments, the present invention relates to methods for identifying potential ligands for PDE10A or homologs or variants thereof comprising: a. displaying the three-dimensional structure of the PDE10A enzyme or homologue or variant thereof, or portions thereof, as defined by the atomic coordinates that are substantially similar to the atomic coordinates listed in FIGURE 4 on a computer screen; b. optionally replacing one or more enzyme amino acid residues listed in SEC. FROM IDENT. NO .: 1, or preferably one or more amino acid residues selected from Leu625, Phe629, Val668, Phe686, Met703, Gln716 and Phe719, in the three-dimensional structure with a different amino acid of natural origin or an unnatural amino acid to exhibit a variant structure; c. optionally conducting ab intio, molecular mechanisms or molecular dynamics calculations in the three-dimensional structure exhibited to generate a modified structure; d. employ the three-dimensional structure, variant structure or modified structure to design or select the ligand; d. synthesize or obtain such a ligand; and. contacting the ligand with the enzyme in the presence of one or more substrates; and f. measure the ability of the ligand to modulate the activity of the enzyme. Those of skill in the art can appreciate that the information obtained by the methods for identifying PDE10A inhibitors and ligands, as described above, can be used to refine or iteratively modify the structure of the original ligand. Thus, once a ligand is found to modulate the activity of the enzyme, the structural aspects of the ligand can be modified to generate a structural analog of the ligand. This analog can then be used in the above method to identify binding ligands. Someone with ordinary skill in the art will know the various ways in which a structure can be modified. In embodiments, preferred ligands include a selective inhibitor of PDE1 OA. In the embodiments, the methods further comprise modifying the structure of the ligand in a computable manner; determine in a computable way the adjustment of the modified ligand using the three-dimensional coordinates described in FIGURE 4, or portions thereof; contacting the modified ligand with the enzyme, or homolog, or variant thereof in an in vitro or in vivo configuration; and measuring the ability of the ligand to modulate the activity of the enzyme. . In an eleventh aspect, the present invention provides pharmaceutical compositions and preparations comprising the inhibitors or ligands designed according to any of the above methods. In one embodiment, a composition is provided which includes an inhibitor or ligand designed or identified by any of the above methods. In another embodiment, the composition is a pharmaceutical composition. The twelfth aspect of the present invention are methods for treating psychotic disorders and a condition such as schizophrenia, illusory disorders and drug-induced psychosis; anxiety disorders such as panic and obsessive-compulsive disorder; and movement disorders including Parkinson's disease and Huntington's disease, which comprise administering pharmaceutical compositions identified by the structure-based design using the atomic coordinates, or portions thereof, listed in FIGURE 4, effective for treating disorders or conditions .

BRIEF DESCRIPTION OF THE FIGURES Figure 1 is an orthogonal view of the modality of the PDE10A in a cord representation. The compound of Formula 1 is shown in a representation of spheres and rods.

The N and C terms of the polypeptide are labeled. A: compound 489 Figure 2 is another orthogonal view of the modality of the compounds of Formula 1 with PDE10A. A: Compound 489 Figure 3 is a schematic diagram showing the interactions of the compound of Formula 1 with PDE10A. TO: Compound 489, B: ligand C binding: ligand-free linkage D: hydrogen bonding and its length E: residues without ligand involved in the hydrophobic contact (s) F: corresponding atoms involved in the hydrophobic contact (s). Figure 4 is a list of X-ray coordinates of the C-terminal catalytic domain crystal of PDE10A as described in the Examples.

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to crystal compositions of PDE10A, atomic X-ray coordinates of 3-D of such a crystalline composition, methods for preparing such compositions, methods for determining the atomic coordinates of 3-D X-rays of crystalline compositions, and methods for using such atomic coordinates together with computational methods to identify the binding site (s), or identify ligands which interact with the binding site (s) to agonize or antagonize PDE10A. For convenience, certain terms used in the specification, examples and appended claims are collected here. Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "affinity" as used herein refers to the tendency of one molecule to associate with another. The affinity of a drug is its ability to bind to its biological target (receptor, enzyme, transport system, etc.) For pharmacological receptors, the affinity can be thought of as the frequency with which the drug, when in proximity to a drug. receiver by diffusion, will reside in the position of a minimum free energy within the force field of that receiver.

The term "agonist" as used herein, refers to an endogenous substance or a drug that can Interacting with a receptor and initiating a physiological or pharmacological response characteristic of that receptor (contraction, relaxation, secretion, enzymatic activation, etc.). The term "analogue" as used herein, refers to a drug or chemical compound whose Structure is related in some way to that of another drug or chemical compound, but whose chemical and biological properties can be very different. The term "antagonist" as used herein refers to a drug or a compound that counterposes the physiological effects of the other. At the receptor level, this is a chemical entity that counterposes the responses associated with the receptor normally induced by another bioactive agent. As used herein, the term "binding site" refers to a specific region (or atom) in a molecular entity that is capable of forming part of a stabilization interaction with another molecular entity. In certain embodiments the term also refers to the reactive parts of a macromolecule that directly participates in its specific combination with another molecule. In other embodiments, a binding site can be understood or defined by the three-dimensional arrangement of one or more amino acid residues within a folded polypeptide. In additional embodiments, the binding site further comprises prosthetic groups, water molecules or metal ions which may interact with one or more amino acid residues. Prosthetic groups, water molecules or metal ions may be apparent from the crystallographic X-ray data, or they may be added to an apo protein or an enzyme using in silico methods. The term "bioactivity" refers to a PDE10 activity that exhibits a biological property conventionally associated with a PDE10A agonist or antagonist, such as a property that would allow the treatment of one or more of the various diseases of the central nervous system. The term "catalytic domain" as used herein, refers to the catalytic domain of the. PDE10A class of enzymes, which characterizes a conserved segment of amino acids in the carboxy-terminal portion of proteins, where this segment has been shown to include the catalytic site of these enzymes. This conserved catalytic domain extends approximately from the residue Thr442 to Asp774 of the full-length enzyme. "To clone" as used herein means obtaining exact copies of a given polynucleotide molecule that uses recombinant DNA technology. In addition, "cloning in" may mean as inserting a first given polynucleotide sequence into a second polynucleotide sequence, preferably so as to result in a functional unit combining the functions of the first and second polynucleotides. For example, without limitation, a polynucleotide from which a fusion protein can be provided by translation, which fusion protein comprises amino acid sequences encoded by the first and second polynucleotide sequences. Specific molecular cloning data can be found in a number of commonly used laboratory protocol books such as Molecular Cloning: A Laboratory Manual, 2a. Ed., By Sambrook, Fritsch and Maniatis (Cold Spring Harbor Laboratory Press: 1989). The term "co-crystallization" as used herein is taken to mean crystallization of a pre-formed protein / ligand complex. The term "complex" or "co-complex" is used interchangeably and refers to a PDE10A molecule or a variant, or PDE10A homologue in covalent or non-covalent association with a substrate or ligand. The term "contact" as used herein applies to in silico, in vitro or in vivo experiments. As used herein, the terms "gene", "recombinant gene" and "genetic construct" refer to a nucleic acid comprising a reading frame encoding a polypeptide, which includes both exon and intron sequences (optionally). The term "intron" refers to a DNA sequence present in a given gene which does not translate into the protein and is generally found among the exons. The term "high affinity" as used herein means strong binding affinity between molecules with a constant dissociation KD of not more than 1 mM. In a preferred case, the KD is less than 100 nM, 10 nM, 1 nM, 100 pM or even 10 pM or less. In a more preferred embodiment, the two molecules can be covalently linked (KD is essentially 0). The term "homologous" as used herein, means a protein, polypeptide, oligopeptide or portion thereof, which preferably has at least 90% amino acid sequence identity with the enzyme PDE10A as described in SEQ. FROM IDENT. NO .: 1, or SEC. FROM IDENT. NO .: 2 or any catalytic domain described herein, or any functional or structural domain of lipid binding protein. The SEC. FROM IDENT. NO .: 1 is a partial amino acid sequence of rattus norvegicus PDE10A wild-type (rat). The SEC. FROM IDENT. NO .: 2 is the amino acid sequence of the wild-type carboxy terminal catalytic domain of rattus norvegicus PDE10A (rat) which was crystallized in the Examples. While the SEC. FROM IDENT. NO .: 3 is the amino acid sequence of wild-type mus musculus (mouse) PDE10A, which is at least 90% identical with the PDE10A enzyme as described in SEC. FROM IDENT. NO .: 1. Those skilled in the art will understand that a set of structure coordinates determined by X-ray crystallography is not within the standard error. As used herein, and for the purpose of this invention, the term "substantially similar atomic coordinates" or atomic coordinates that are "substantially similar" refers to any set of structure coordinates of PDE10A or PDE10A homologs, or variants of PDE10A, polypeptide fragments, described by the atomic coordinates that have an average root deviation of squares for the atomic coordinates of the protein structure atoms (N, Ca, C and O) of less than about 1.5, 1.2, 1.0 , 0.7, 0.5 or even 0.2 A, when overlapping using structure coordinate structure atoms listed in FIGURE 4. For the purpose of this invention, structures that have substantially similar coordinates as those listed in FIGURE 4 will be considered identical to the coordinates listed in FIGURE 4. The term "substantially similar" also applies to a waste assembly of amino acids that may or may not form a contiguous polypeptide chain, but whose three-dimensional arrangement of atomic coordinates has an average root deviation of squares for the atomic coordinates of the protein structure atoms (N, Ca, C, and O) or atoms side chain, less than about 1.5, 1.2, 1.0, 0.7, 0.5 or even 0.2 A when superimposed using structure atoms, or the side chain atoms of the atomic coordinates of the same or similar amino acids from the coordinates listed in FIGURE 4. To further clarify, without intending to be limiting, an example of an amino acid assembly may be the amino acid residues that form a binding site in an enzyme. These residues may have one or more intermediate residues which are distant from the binding site, and therefore may interact minimally with a ligand at the binding sites. In such cases, the binding site can be defined for the purpose of the structure based on the design of the drug as comprising only a bundle of amino acid residues. For example, in the case of PDE10A, the amino acid residues Leu625, Phe629, Val668, Phe686, Met703, Gln716 and Phe719 of SEQ. FROM IDENT. NO .: 1 are known to be close to or on the link site. Thus, any molecular assembly that has an average root deviation of squares from the atomic coordinates of the structure atoms of the protein (N, Ca, C and O) or the side chain atoms, of one or more of Leu625, Phe629, Val668, Phe686, Met703, Gln716 or Phe719 of SEQ. FROM IDENT. NO .: 1, or any conservative substitutions thereof, of less than about 1.5, 1.2, 1.0, 0.7, 0.5 or even 0.2 A when overlapping will be considered substantially similar to the coordinates listed in FIGURE 4. Those skilled in the art. They understand that the "substantially similar" atomic coordinates are considered identical to the coordinates, or portions thereof, listed in FIGURE 4.

Those skilled in the art will further understand that the coordinates listed in FIGURE 4 or portions thereof can be transformed into a different set of coordinates using various mathematical algorithms without departing from the present invention. For example, the coordinates listed in FIGURE 4, or portions thereof, can be transformed by algorithms which translate or rotate the atomic coordinates. Alternatively, molecular mechanics, molecular dynamics or intio ab algorithms can modify the atomic coordinates. The atomic coordinates generated from the coordinates listed in FIGURE 4, or portions thereof, that use any of the aforementioned algorithms will be considered identical to the coordinates listed in FIGURE 4. The term "in silico" as used in the present, it refers to experiments carried out using computer simulations. In certain modalities, in silico methods are molecular modeling methods where three-dimensional models of macromolecules or ligands are generated. In other embodiments, in silico methods comprise computably evaluating ligand binding interactions. The term "ligand" describes any molecule, for example, protein, peptide, peptidomimetics, oligopeptides, small organic molecule, polysaccharide, polynucleotide, etc., which is designed or developed with reference to the crystal structure of PDE10A as represented by the atomic coordinates listed in FIGURE 4. In one aspect the ligand is an agonist, so the molecule over-regulates (ie, activates or stimulates for example, agonizing or increasing potency) activity, while in another aspect of the invention the ligand is an inhibitor or an antagonist, whereby the molecule de-regulates (ie, inhibits or suppresses, for example, antagonizing, decreasing or inhibiting) the activity. The term "modular" as used herein refers to both over-regulation (ie, activation or stimulation, eg, agonizing or increasing power) and de-regulation (i.e., inhibition or suppression, for example, antagonizing, decreasing or inhibiting) an activity. The term "pharmacophore" as used herein, refers to the group of spherical and electronic characteristics of a particular structure that is necessary to ensure optimal supramolecular interactions with a specific biological target structure and to drive (or block) its response biological A pharmacophore may or may not represent a real molecule or an actual association of functional groups. In certain modalities, a pharmacophore is an abstract concept that constitutes the common molecular interaction capabilities of a group of compounds towards their objective structure. In certain modalities, the term can be considered as the largest common denominator shared by a set of active molecules. The pharmacological descriptors are used to define a pharmacophore, including H bond, hydrophobic and electrostatic interaction sites, defined by atoms, ring centers and virtual points. Accordingly, in the context of the ligands of the enzyme, such as, for example, agonists or antagonists, a pharmacophore may represent a group of steric and electronic factors which are necessary to ensure supramolecular interactions with a specific biological target structure. As such, a pharmacophore can represent a template of chemical properties of an active site of a protein / enzyme - which represents these properties of spatial relationship to each other - that theoretically define a ligand that would bind to that site. The term "precipitant" as used herein includes any substance which, when added to a solution, causes a precipitate to form or develop crystals. Examples of precipitants within the scope of this invention include, but are not limited to alkali metal salts (eg, Li, Na or K), or alkaline earth salts (eg, Mg or Ca) and transition metal salts (eg, Mn or Zn). The counterions common to metal ions include, but are not limited to halides, phosphates, citrates and sulfates. The term "pro-drug" as used herein, refers to drugs that, once administered, are chemically modified by metabolic processes in order to become pharmaceutically active. In certain embodiments the term also refers to any compound that undergoes bio-transformation before exhibiting its pharmacological effects. The pro-drugs can thus be visualized as drugs containing specialized non-toxic protective groups used in a transient manner to alter or eliminate properties, usually undesirable, in the progenitor molecule. The term "receptor" as used herein refers to a protein or protein complex within or on a cell that recognizes and binds specifically to a compound that acts as a molecular messenger (neurotransmitter, hormone, lymphokine, lectin, drug, etc.). In the broadest sense, the term "receptor" is used interchangeably with any specific drug binding site (as opposed to a non-specific one, such as the link to plasma proteins), also including nucleic acids such as DNA. The term "recombinant protein" refers to a polypeptide which is produced by recombinant DNA techniques, wherein generally, the DNA encoding a polypeptide is inserted into a suitable expression vector which in turn is used to transform a host cell that produces the polypeptide encoded by the DNA. This polypeptide may be one that is naturally expressed by the host cell, or it may be heterologous to the host cell or the host cell may have been designed to have lost the ability to express the polypeptide which is otherwise expressed in the form of a type. wild from the host cell. The polypeptide can also be, for example, a fusion polypeptide: In addition, the phrase "derived from", with respect to a recombinant gene, means that it includes within the meaning of "recombinant protein" those proteins that have an amino acid sequence of a native polypeptide, or an amino acid sequence similar thereto which is generated by mutations, including substitutions, deletions and truncation of a naturally occurring form of the polypeptide. As used herein, the term "selective PDE10A inhibitor" refers to a substance, for example an organic molecule that effectively inhibits an enzyme from the PDE10A family to a greater degree than any other PDE enzyme, particularly any enzyme from families of PDE 1-9 or any PDE11 enzyme. In one embodiment, a selective PDE10A inhibitor is a substance, for example, a small organic molecule having a Ki for inhibition of PDE10A that is less than about one-half, one-fifth or one-tenth of K, that the substance has for inhibition of any other PDE enzyme. In other words, the substance inhibits the activity of PDE10A to the same degree in a concentration of about half, one fifth, one tenth or less of the concentration required for any other PDE enzyme. In general, a substance is considered to effectively inhibit PDE10A if it has an IC50 of Ki of less than or about 10 mM, 1 mM, 500 nM, 100 nM, 50 nM or even 10 nM. As used herein the term "small molecules" refers to preferred drugs that are available orally (as opposed to proteins that must be administered by injection or topically). The size of small molecules is generally under 1000 Daltons, but many estimates seem to vary between 300 to 700 Daltons. By "therapeutically effective" amount is meant that amount which is capable of at least partially reversing the symptoms of the disease. A therapeutically effective amount can be determined on an individual basis and will be based, at least in part, in a consideration of the species of the mammal, the size of the mammal, the type of delivery system used, and the type of administration in relation to the progress of the disease. A therapeutically effective amount can be determined by someone skilled in the art employing such factors and using no more than routine experimentation. As used herein, the term "transfection" means the introduction of a nucleic acid, for example, through an expression vector, into a recipient cell by nucleic acid mediated gene transfer. "Transformation" refers to a process in which a genotype of the cell is changed as a result of cellular incorporation of the exogenous DNA or RNA and for example, the transformed cell expresses a recombinant form of a polypeptide or, in the In case of the uncoded expression from the transformed gene, the expression of the naturally occurring form of the polypeptide is interrupted. The term "variants" in relation to the polypeptide sequence in SEC. FROM IDENT. NO .: 1 or SEC. FROM IDENT. NO .: 2, includes any substitution of the variation of, modification of, replacement of, deletion of, or addition of one or more amino acids from, or the sequence provides a resulting polypeptide sequence for an enzyme that it has PDE10A activity. Preferably, the variant, homologue, fragment or portion of the SEC. FROM IDENT. NO .: 1 or SEC. FROM IDENT. NO .: 2, comprises a polypeptide sequence of at least 5 contiguous amino acids, preferably at least 10 contiguous amino acids, preferably at least 15 contiguous amino acids, preferably at least 20 contiguous amino acids, preferably at least 25 contiguous amino acids, or preference at least 30 contiguous amino acids. The term "vector" refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. One type of preferred vector is an episome, i.e., a nucleic acid capable of extra-chromosomal replication. Preferred vectors are those capable of replication and / or autonomous expression of nucleic acids to which they bind. Vectors capable of directing the expression of genes to which they are operatively linked are referred to herein as "expression vectors". In general, expression vectors of utility in recombinant DNA techniques are often in the form of "plasmids" which generally refer to double-stranded, circular DNA loops which, in their vector form, do not bind to the chromosome. In the present specification, "plasmid" and "vector" are used interchangeably as the plasmid, is the most commonly used form of the vector. However, the invention is intended to include other forms of expression vectors, which perform equivalent functions and which will be known in the art subsequently to this. The following amino acid abbreviations are used throughout this description: A = Ala = Alanine T = Thr = Threonine V = Val = Valine C = Cys = Cysteine L = Leu = Leucine Y = Tyr = Tyrosine I = lie = Isoleucine N = Asn = Asparagine P = Pro = Proline Q = Gln = Glutamine F = Phe = Phenylalanine D = Asp = Aspartic Acid W = Trp = Tryptophan E = Glu = Glutamic Acid M = Met = Methionine K = Lys = Lysine G = Gly = Glycine R = Arg = Arginine S = Ser = Serine H = His = Histidine A. Clones and Expressions The nucleotide sequence encoding a PDE10A polypeptide, or functional fragment, including the C-terminal peptide fragment of the catalytic domain of PDE10A protein , derivatives or analogs thereof, including a chimeric protein thereof, can be inserted into an appropriate expression vector, i.e., a vector which contains the necessary elements for the transcription and translation of the protein coding sequence. tada The elements mentioned above are referred to herein as a "promoter". In this way, the nucleic acid encoding a PDE10A polypeptide of the invention or a functional fragment comprising the C-terminal peptide fragment of the catalytic domain of PDE10A protein, derivatives or analogs thereof, is operationally associated with a promoter in a vector of expression of the invention. In preferred embodiments, the expression vector contains the nucleotide sequence encoding the polypeptide comprising the amino acid sequence spanning amino acids Thr442 to Asp774 listed in SEQ. FROM IDENT. NO .: 1. Both cDNA and genomic sequences can be cloned and expressed under the control of such regulatory sequences. An expression vector also preferably includes an origin of replication. Necessary transcription and translation signals can be provided in a recombinant expression vector. As detailed below, all genetic manipulations described for the PDE10A gene in this section can also be used for genes encoding a functional fragment, including the C-terminal peptide fragment of the PDE10A protein catalytic domain, derivatives or analogs of the same, including a chimeric protein thereof. Potential host vector systems include but are not limited to mammalian cell systems infected with viruses (e.g., Vaccinia virus, adenovirus, etc.), insect cell systems infected with virus (e.g., baculovirus); microorganisms such as yeast containing yeast vectors; or bacteria transformed with bacteriophage; DNA, plasmid DNA, or cosmid DNA. The expression elements of vectors vary in their resistances and specificities. Depending on the host vector system used, any of a number of suitable transcription and translation elements can be used. A recombinant PDE10A protein of the invention can be expressed chromosomally, after integration of the recombination coding sequence. In this regard, any number of amplification systems can be used to achieve high levels of stable gene expression (See Sambrook et al., 1989, infra, the pertinent description which is incorporated herein by reference in its entirety). A cell suitable for purposes of this invention is one in which the recombinant vector comprising the nucleic acid encoding the PDE10A protein is cultured in an appropriate cell culture medium under conditions that make possible the expression of the PDE10A protein by the cell. Any of the methods previously described for the insertion of the DNA fragments into a cloning vector can be used to construct expression vectors containing a gene consisting of appropriate transcription / translation control signals and protein coding sequences. These methods may include in vitro and synthetic recombinant DNA techniques, and in vivo recombination (genetic recombination). The expression of the PDE10A protein can be controlled by any promoter / enhancer element known in the art, but these regulatory elements must be functional in the sectioned host for expression. Vectors containing an amino acid encoding a PDE10A protein of the invention can be identified by four general methods: (1) PCR amplification of the desired plasmid DNA or specific mRNA, (2) nucleic acid hybridization, (3) presence or absence of the genetic functions of the selection marker, and (4) the expression of inserted sequences. In the first method, the nucleic acids can be amplified by PCR to provide detection of the amplified product. In the second method, the presence of a foreign gene inserted into an expression vector can be detected by nucleic acid hybridization using probes comprising sequences that are homologous to an inserted marker gene. In the third method, the recombinant vector / host system can be identified and selected based on the presence or absence of certain genetic functions of the "selection marker" (e.g., beta-galactosidase activity, thymidine kinase activity, resistance to antibiotics, transformation of phenotype, occlusion of corporal formation in baculovirus, etc.), caused by the. insertion of foreign genes in the vector. In another example, if the nucleic acid encoding the PDE10A protein is inserted into the genetic sequence of the "selection marker", the recombinant vectors containing the PDE10A protein insert can be identified by the absence of the genetic function of the PDE10A protein. . In the fourth method, recombinant expression vectors can be identified by evaluating the activity, biochemical or immunological characteristics of the gene product expressed by the recombinant vector, as long as the expressed protein assumes a functionally active conformation. A wide variety of host / expression vector combinations can be employed by expressing the DNA sequences of this invention as is known to those skilled in the art. Once a particular recombinant DNA molecule is identified and isolated, several methods known in the art can be used to propagate them. Once a suitable host system and developmental conditions are established, the recombinant expression vectors can be propagated and prepared in quantity. As previously explained, expression vectors that can be used include, but are not limited to the following vectors or their derivatives; human or animal viruses such as Vaccinia virus or adenovirus; insect viruses such as baculovirus; yeast vectors; bacteriophage vectors (eg, lambda), and plasmid and cosmid DNA vectors, to name but a few. The vectors can be introduced into the desired host cells by methods known in the art, for example, transfection, electroporation, microinjection, transduction, cell fusion, DEAE dextran, calcium phosphate precipitation, lipofection (lysosome fusion), the use of a genetic cannon or a DNA vector transporter (see for example, Wu et al., 1992, J. Biol. Chem. 267: 963-967; WU and Wu, 1988, J. Bioi. Chem. 263: 14621-14624; Hartmut et al., Canadian Patent Application No. 2,012,311, filed March 15, 1990). B. Crystal and Spatial Groups X-ray structure coordinates define a unique configuration of points in space. Those skilled in the art understand that a set of structure coordinates for a protein or a protein / ligand complex or a portion thereof, defines a relative set of points which, in turn, define a three-dimensional configuration. A similar or identical configuration can be defined by a completely different set of coordinates, as long as the distances and angles between the atomic coordinates remain essentially the same. In addition, a scalable point configuration can be defined by increasing or decreasing the distances between the coordinates by a scalar factor while maintaining essentially the same angles. One aspect of the present invention relates to a crystalline composition preferably comprising a polypeptide with an amino acid sequence spanning amino acids Thr442 to Asp774 listed in SEQ. FROM IDENT. NO .: 1. In one embodiment, the present invention describes a crystalline PDE10A molecule comprising a polypeptide with an amino acid sequence spanning amino acids Thr442 to Asp774 listed in SEQ. FROM IDENT. NO .: 1, combined with one or more ligands. In another embodiment, the crystallized complex is characterized by the structural coordinates listed in FIGURE 4 or portions thereof. In certain embodiments, the ligand atoms are within about 4, 7 or 10 angstroms of one or more amino acids of PDE10A in SEC. FROM IDENT. NO .: .1, preferably selected from Leu625, Phe629, Val668, Phe686, Met703, Gln716 and Phe719. One embodiment of the crystallized complex is characterized as belonging to the space group R3 and has cell dimensions of a = 120.6, b = 120.6, c = 82.1 A, a = b = 90.0, g = 120 °. This embodiment is encompassed by the structural coordinates of FIGURE 4. The ligand can be a small molecule which binds to a catalytic domain of PDE10A defined by SEC. FROM IDENT. NO .: 2, or portions thereof, with a Ki of less than about 10 mM, 1 mM, 500 nM, 100 nM, 50 nM or even 10 nM. In a certain embodiment, the ligand is the compound of Formula I (6,7-dimethoxy-4- [8 ~ (4-methyl-piperazin-1-sulfonyl) -3,4-dihydro-1 H-isoquinolin-2 il] -quinazolian). In certain embodiments, the ligand is a substrate or analog of PDE10A substrate. In certain embodiments, the ligand (s) may be a competitive or non-competitive inhibitor of PDE10A. In certain embodiments, the ligand is a covalent inhibitor of PDE10A. Various computational methods can be used to determine whether a molecule or a portion of the binding cavity thereof is "structurally equivalent", defined in terms of its three-dimensional structure, to all or part of PDE10A or its linker cavities. Such methods can be carried out in current software applications, such as the molecular similarity application of QUANTA (Accelrys Inc., San Diego, Calif.). The application of molecular similarity allows comparisons between different structures, different conformations of the same structure, and different parts of the same structure. The procedure used in molecular similarity to compare structures is divided into four stages: (1) load structures that are compared; (2) optionally define the atomic equivalences in these structures; (3) perform an adjustment operation; and (4) analyze the results. Each structure is identified by a name. A structure is identified as the objective (that is, the fixed structure); all the remaining structures are structures in operation (ie structures in motion). Since the atomic equivalence within the applications of molecular similarity is defined by the input of the user, for the purpose of this invention equivalent atoms are defined as atoms of protein structure (N, Ca, C and O) for all conserved residues between the two structures that are compared. A conserved residue is defined as a residue that is structurally or functionally equivalent (See Table 4 below). In certain modalities, rigid adjustment operations are considered. In other modalities, flexible adjustment operations may be considered. When a rigid adjustment method is used, the structure in operation is translated and rotated to obtain an optimal fit with the target structure. The adjustment operation uses an algorithm that calculates the translation and optimal rotation that is applied to the structure in motion, so that the average root difference of squares of the adjustment over the specified pairs of equivalent atoms is an absolute minimum. This number, given in angstroms, is reported by the application of molecular similarity. For the purpose of this invention, any molecule or molecular complex or binding cavity thereof or any portion thereof, which has an average root deviation of squares of structure atoms of the conserved residue (N, Ca, C and O) ) of less than about 1.5 A, 1.0 A, 0.7 A, 0.5 A, or even 0.2 A, when superimposed on the relevant structure atoms described by the reference structure coordinates listed in FIGURE 4, is considered "structurally equivalent" to the reference molecule. That is, the crystal structures of those portions of the two molecules are substantially identical, within the acceptable error. Structurally equivalent molecules or molecular complexes, particularly preferred are those that are defined by the complete set of structural coordinates listed in FIGURE 4, more or less to an average root deviation of squares from the conserved structure atoms of those amino acids of no more than 2.0 A. More particularly, the average root deviation of squares is less than about 1.0 A.

The term "average root deviation of squares" means the square root of the arithmetic mean of the squares of the deviations. This is a way to express the deviation or variation from a trend or object. For purposes of this invention, the "mean square root deviation" defines the variation in the structure of a protein from the PDE10A structure or a portion of the link cavity thereof, as defined by the structural coordinates of PDE10A described herein. The defined x-ray coordinates of the catalytic domain of PDE10A (amino acids 442 to 774 are listed in SEQ ID NO: 2), are combined with the compound of Formula 1 (6,7-dimethoxy-4- [ 8- (4-methyl-piperazin-1-sulfonyl) -3,4-dihydro-1 H-isoquinolin-2-yl] -quinazoline), Zn2 +, Mg2 +, and 312 water molecules are listed in FIGURE 4. Two Orthogonal views of the molecule are shown in FIGURE 1 and FIGURE 2 and the details of the interactions of the inhibitor with protein are shown in FIGURE 3. The structure is composed of a single domain of fourteen helices a and two helices 3? 0 arranged in a compact fold (FIGURE 1). The number of the propeller is shown later. The following numbering conversion is established by Xu et al., Science, 288: 1822-25 (2000), and the start and end points of the helices are determined according to Kabsch and Sander, Biopolymers, 22 ( 12): 2577-637 (1983). to propellers Waste margin helices 310 Remaining margin H1 454-461 A1 666-669 H3 476-487 A2 702-710 H5 495-507 H6 517-532 H7 540-552 H8 562-568 H9 571-575 H10 580-594 H11 606-622 H12 625-640 H13 649-664 H14 672-694 H15a 712-722 H15b 724-734 H16 739-756 The two metal ions are in the catalytic site. The first is determined to be Zn +, by analogue with PDE4b, and from an analysis of its coordination geometry. The metal is coordinated by His553 (Ne2-Zn, 2.1A), His519 (Ne2-Zn 2.0Á), Asp554 (Od2-Zn, 2.1A), Asp664 (Od2-Zn 2.2Á) and one water molecule (O- Zn, 1.7A). These residues are completely conserved through the genetic family of PDE. The second metallic ion is coordinated to Asp554 (Od1-Zn 1.9Á) and to an aqueous network that stabilizes the metallic environment. Due to the coordination geometry and the relative observed electron density, this second metal ion has been refined as an Mg2 + according to a similar observation in the structure of PDE4. (Xu et al., Science, 288: 1822-25 (2000)).

One molecule of the inhibitor, 6,7-dimethoxy-4- [8- (4-methyl-piperazin-1-sulfonyl) -3,4-dihydro-1H-isoquinolin-2-yl] -quinazoline. The compound of Formula 1 is observed bound within the active site. The inhibitor binding site is linked by H14, H15a and H15b on one side, and by the N-terminus of H12 and the two helices 3-? Or A1 and A2. The protein inhibitor interactions are shown schematically in FIGURE 2. Most interactions between the inhibitor and the protein are hydrophobic in nature; with only two observed hydrogen bonds (FIGURE 2). Both bonds h are between fully conserved Gln716 Ne2 and methoxy oxygens 014 (3.0A) and 017 (3.1A). The quinazoline ring of the inhibitor appears to perform a strong p-stacking interaction with Phe719 and an edge stacking interaction with Phe686. The sulfonamide-piperazine group does not direct interactions with the protein. Accordingly, the present invention provides a molecule or molecular complex that includes at least a portion of PDE10A and / or a substrate binding cavity. In one embodiment, the PDE10A binding cavity includes the amino acids listed in Table 1, preferably the amino acids listed in Table 2, and more preferably the amino acids listed in Table 3, the binding cavity is defined by a set of points that have an average root deviation of squares of less than about 1.5, 1.2, 1.0, 0.7, 0.5 or even 0.2 A, from points representing the structure atoms of the amino acids in Tables 1-3. In another embodiment, the PDE10A substrate binding cavity includes the amino acids selected from Leu625, Phe629, Val668, Phe686, Met703, Gln716 and Phe719 from SEQ. FROM IDENT. NO .: 1. Table 1. Residues near the binding cavity in the catalytic domain of PDE10A. The identified residues are 10 A away from the compound of Formula 1 Table 2: Residues near the binding cavity in the catalytic domain of PDE10A. The identified residues are 7A away from the compound of Formula 1 Table 3: Residues near the binding cavity in the catalytic domain of PDE10A. The identified residues are 4 A away from the compound of Formula 1.

C. Isolated Polypeptides and Variants One embodiment of the invention discloses an isolated polypeptide consisting of a portion of PDE10A that functions as the binding site when folded in the appropriate 3-D orientation. One embodiment is an isolated polypeptide comprising a portion of PDE10A, wherein the portion initiates at approximately the amino acid residue Thr442, and terminates at approximately the amino acid residue Asp774 as described in SEQ. FROM IDENT. NO .: 1, or a sequence that is at least 90%, 95% or 98% homologous to a polypeptide with an amino acid sequence spanning amino acids Thr442 to Asp774 as listed in SEQ. FROM IDENT. NO .: 1, such as, for example, the polypeptide of the wild type muscle musculus (mouse) PDE10A enzyme, described in SEQ. FROM IDENT. NO .: 3. Another embodiment of the invention comprises crystalline compositions comprising variants of PDE10A. The variants of the present invention can have an amino acid sequence that is different by one or more amino acid substitutions to the sequence described in SEQ. FROM IDENT. NO .: 1 or SEC. FROM IDENT. NO .: 2. The modalities which comprise eliminations and / or amino acid additions are also contemplated. The variant may have conservative changes (amino acid similarity), wherein a substituted amino acid has similar structural or chemical properties, for example, the replacement of leucine with isoleucine. The guidance for determining which and how many amino acid residues can be substituted, inserted or deleted without adversely affecting the proposed biological or pharmacological activity can be reasonably inferred in view of this description, and can furthermore be found using computer programs well known in the art, for example , DNAStar® software. The amino acid substitutions can be made for example, on the basis of similarity in polarity, charge, solubility, hydrophobicity, hydrophilicity and / or the antipathetic nature of the residues as long as a biological and / or pharmacological activity of the native molecule is retained. The negatively charged amino acids include aspartic acid and glutamic acid; positively charged amino acids include lysine and arginine; amino acids with uncharged polar head groups having similar hydrophilicity values include leucine, isoleucine and valine; amino acids with aliphatic header groups include glycine, alanine; asparagine, glutamine, serine; and amino acids with aromatic side chains include threonine, phenylalanine and tyrosine. Examples of conservative substitutions are set forth in Table 4 as follows: Table 4: "Homology" is a measure of the identity of nucleotide sequences or amino acid sequences. In order to characterize the homology, the subject sequences are aligned so that the highest homology percentage (equivalence) is obtained, after introducing openings, if necessary, to achieve the maximum percentage of homology. Terminal extensions N and C will not be construed as affecting homology. "Identity" per se has a recognized significance in the art and can be calculated using published techniques. The methods of the computer program for determining the identity between two sequences, for example, include DNAStar® software (DNAStar Inc., Madison, Wl); the GCG® program package (Devereux, J., et al., Nucleic Acids Research (1984) 12 (1): 387); BLASTP, BLASTN, FASTA (Atschul, S.F. et al., J. Molec Biol (1990) 215: 403). The homology (identity) as defined herein is conventionally determined using the well-known computer program, BESTFIT® (Wisconsin Sequence Analysis Package, Version 8 for Unix, Genetics Computer Group, University Research Park, 575 Science Drive, Madison, Wl 53711). When using BESTFIT® or any other sequence alignment program (such as the Clustal algorithm from the MegAlign software (DNAStar®) to determine if a particular sequence is for example, approximately 90% homologous to a reference sequence, according to to the present invention, the parameters are set so that the percent identity is calculated over the total length of the reference nucleotide sequence or an amino acid sequence and those openings in homology of up to about 90% of the total number of nucleotides in the reference sequence Ninety percent homology is therefore determined, for example, using the BESTFIT® program with established parameters so that the percent identity is calculated over the total length of the reference sequence, by example, SEQ ID NO: 1, and wherein up to 10% of the amino acids in the reference sequence can replace with another amino acid. The percentage homologies are determined likewise, for example, to identify preferred species, within the scope of the appended claims thereto, which resides within the range of about 90% to 100% homology to the SEC. FROM IDENT. NO .: 1 as well as the link site thereof. As noted above, the N or C terminal extensions should not be interpreted as affecting homology. Thus, when comparing two sequences, the reference sequence is generally the shortest of the two sequences. This means that for example, if a sequence of 50 nucleotides in length with precise identity to a region of 50 nucleotides within a polynucleotide of 100 nucleotides is compared, there is 100% homology as opposed to only 50% homology. Although the natural polypeptide of SEQ. FROM IDENT. NO .: 1 and a variant polypeptide can only possess a certain percentage of identity, for example, 90%, they are in fact likely to possess a higher degree of similarity, depending on the number of dissimilar codons that are conservative changes. Conservative amino acid substitutions can be made frequently in a protein without altering any of the conformation or function of the protein. The similarity between two sequences includes direct similarities as well as substitutes for conserved amino acids which possess similar structural or chemical properties eg, similar charge as described in Table 4. The percentage of similarity (conservative substitutions) between two polypeptides can also be classified by comparing the amino acid sequences of the two polypeptides using programs well known in the art, including the BESTFIT program, using default settings to determine similarity. A further embodiment of the invention is a crystal comprising the coordinates of FIGURE 4, wherein the amino acid sequence is represented by SEC. FROM IDENT. NO .: 1. A further embodiment of the invention is a crystal comprising the coordinates of FIGURE 4, wherein the amino acid sequence is at least 90%, 95% or 98% homologous to the amino acid sequence represented by the SEC . FROM IDENT. NO .: 1. Various methods for obtaining atomic coordinates of structurally homologous molecules and molecular complexes using homology modeling are described in US Pat. No. 6,356,845, which is incorporated herein by reference in its entirety. D. Structure Based on Drug Design Once the three-dimensional structure of a crystal comprising a PDE10A protein, a functional domain thereof, the homologue or variant thereof, is determined, a potential ligand (antagonist or agonist) can be examined through the use of the computer model using a coupling program such as GRAM, DOCK or AUTODOCK (See for example, Morris et al., J. Computational Chemistry, 19: 1639-1662 (1998)). This procedure may include an in silico fit of potential ligands to the crystal structure of PDE10A to determine how the shape and chemical structure of the potential ligand will complement or interfere with the catalytic domain of PDE10A. (Bugget et al., Scientific American, December: 92-98 (1993); West et al., TIPS, 16: 67-74 (1995)). Computer programs can also be used to estimate the attraction, repulsion and spherical obstruction of the ligand to the binding site. Generally, the narrower the fit (for example, the lower the spherical obstruction, and / or the greater the attractive force) the more potent the potential drug will be since these properties are consistent with a narrower link constant. In addn, the more specificity in the design of a potential drug, the more likely that the drug does not interfere with the properties of other proteins. This will minimize potential side effects due to unwanted interactions with other proteins. One embodiment of the present invention relates to a method for identifying an agent that binds to a binding site in the catalytic domain of PDE10A wherein the binding site comprises amino acid residues Leu625, Phe629, Val668, Phe686, Met703, Gin716 and Phe719 of the SEC. FROM IDENT. NO .: 1, which comprises contacting PDE10A with a test ligand under suitable condns to bind the test ligand to the binding site, and determining whether the test ligand binds to the binding site, where if the link, the test ligand is an agent that binds to the binding site. In certain modals, the test can be carried out in silico using a variety of molecular modeling software algorithms including, but not limited to DOCK, ALADDIN, CHARMM, AFFINITY, C2-LIGAND FIT, Catalyst, LUDI, CAVEAT and CONCORD simulations ( Brooks, et al., CHARMM: a program for macromolecular energy, minimization, and dynamic calculations J. Comp.Chem 1983, 4: 187-217; EC Meng, BK Shoichet &Kuntz.D Automated coupling with energy based evaluation in J Comp Chem 1992,13: 505-524 In another embodiment, a potential ligand can be obtained by selecting a random peptide library produced by a recombinant bacteriophage e.g., (Scott and Smith, Science, 249: 386-390. (1990), Cwirla et al., Proc. Nati Acad. Sci., 87: 6378-6382 (1990), Devlin et al., Sciences, 249: 404-406 (1990)) or a chemical library, or the like A ligand selected in this way can then be systematically modified by programs more than computer modeling until one or more promising potential ligands are identified. Such analyzes have shown that they are effective in the development of HIV protease inhibitors. (Lam et al., 5 Science 263: 380-384 (1994); Wlodawer et al., Ann. Rev. Biochem. 62: 543-585 (1993); Appelt, Perspectives in Drug Discovery and Design 1: 23-48 (1993), Erickson, Perspectives in Drug Discovery and Design 1: 109-128 (1993)). Such computer modeling allows the selection of a limited number of rational chemical modifications, so opposed to the innumerable number of essentially random chemical modifications that could be made, of which either could lead to a useful drug. Each chemical modification requires additional chemical steps, which although are reasonable for the synthesis of a limited number of compounds, it quickly becomes overwhelming if all the possible modifications that need to be modified are really synthesized. In this way, through the use of the three-dimensional structure described here and modeling by As a computer, a large number of these compounds can be quickly selected on a computer screen, and few probable candidates can be determined without the laborious synthesis of non-expressed numbers of compounds. Once a potential ligand (agonist or . antagonist) is identified, it can be selected from a library of chemicals since they are commercially available from the larger chemical companies or alternatively the potential ligand can be synthesized de novo. As mentioned above, the de novo synthesis of one or even a relatively small group of specific compounds is reasonable in the technique of drug design. The potential ligand can be placed within any standard binding assay as known * well by those skilled in the art to test its effect on PDE10A activity. When a suitable drug is identified, a complementary crystal comprising a protein-ligand complex formed between a PDE10A protein and the drug can be developed. Preferably, the crystal effectively diffracts X-rays that allow the determination of atomic coordinates of the protein-ligand complex at a resolution of less than 5.0 Angstroms, more preferably less than 3.0 Angstroms, and even more preferably less than 2.0 Angstroms. The three-dimensional structure of the complementary crystal can be determined by Molecular Replacement Analysis. Molecular replacement involves the use of a three-dimensional structure known as a search model to determine the structure of a closely related molecule or the protein-ligand complex in a new crystal form. The measured X-ray diffraction properties of the new crystal are compared to the search model structure to calculate the position and orientation of the protein in the new crystal. Computer programs that may be used include: X-PLOR and AMORE (J. Navaza, Acta Crystallographics ASO, 157-163 (1994)). Once position and orientation are known, an electron density map can be calculated using the search model to provide X-ray phases. Later, the electron density is inspected for structural differences, and the search model is modify to conform the new structure. By using this method, it is possible to use the claimed structure of PDE10A to solve the three-dimensional structures of any PDE10A combined with a new ligand. Other computer programs that can be used to solve the structures of such STAT crystals include QUANTA; CHARMM; INSIGHT; SYBYL; MACROMODEL; and ICM. Various in silico methods for screening, designing or selecting ligands are described in US Pat. No. 6,356,845, the pertinent description of which is incorporated herein by reference. E. Ligands In one aspect, the present invention describes ligands which interact with a PDE10A catalytic domain binding site defined by a set of points having an average root deviation of squares of less than about 2.0 A from dots. which represent the structure atoms of the amino acids represented by the structure coordinates listed in FIGURE 4. A further embodiment of the present invention comprises binding agents which interact with a PDE10A binding site defined by a set of points having an average root deviation of squares of less than about 2.0, 1.7, 1.5, 1.2, 1.0, 0.7, 0.5 or even 0.2 A from points representing the structure atoms of the amino acids represented by the structure coordinates listed in FIGURE 4. Such modalities represent variants of the PDE10A crystal. In another aspect, the present invention describes ligands which bind to a correctly folded polypeptide comprising an amino acid sequence spanning amino acids 442 to 774 listed in SEQ. FROM IDENT. NO.:1, or a counterpart or variant thereof. In certain embodiments, the ligand is a competitive or non-competitive inhibitor of PDE10A. In certain embodiments the ligand inhibits PDE10A with an IC 50 of Ki of less than about 10 mM, 1 M, 500 nM, 100 nM, 50 nM or 10 nM. In certain embodiments, the ligand inhibits PDE10 with a K, which is less than about half, one-fifth, one-tenth of K, which the substance has for the inhibition of any other PDE enzyme. In other words, the substance inhibits PDE10A activity to the same degree in a concentration of about half, one fifth, one tenth or less of the concentration required for any other PDE enzyme. One embodiment of the present invention relates to ligands, such as proteins, peptides, peptide mimetics, small organic molecules, etc., designed or developed with reference to the crystal structure of PDE10A as represented by the coordinates presented herein. FIGURE 4, and portions thereof. Such binding agents interact with the PDE10A binding site represented by one or more amino acid residues selected from Leu625, Phe629, Val668, Phe686, Met703, Gln716 and Phe719. F. Automated Storage Media The transformation of the structure coordinates for all or a portion of PDE10A, or the PDE10A / ligand complex or one of its binding cavities, for structurally homologous molecule as defined below, or for equivalents The structural features of any of these molecules or molecular complexes as defined above, in three-dimensional graphical representations of the molecule or complex can be conveniently achieved through the use of commercially available software. The invention thus further provides an automated storage means comprising a data storage material encoded with automated data which, when using a programmed machine with instructions for using such data, is capable of displaying a three-dimensional graphic representation of any of the molecule or molecular complexes of this invention that has been described above. In a preferred embodiment, the automated data storage means comprises a machine programmed with instructions for using such data, it is capable of displaying a three-dimensional graphic representation of a molecule or molecular complex as defined above. In another preferred embodiment, the automated data storage medium is capable of displaying a three-dimensional graphic representation of a molecule or a molecular complex defined by the structure coordinates of the amino acids listed in FIGURE 4, plus or minus an average root deviation of squares from the structure atoms of such amino acids of not more than 2.0 A. In an alternative embodiment, the automated data storage means comprises a data storage material encoded with a first set of automated data which comprises the Fourier transform of the structural coordinates established in FIGURE 4, and which, when using a programmed machine with instructions to use such data, can be combined with a second set of automated data comprising the X-ray diffraction pattern of a molecule or molecular complex to determine at least one portion of the structural coordinates that correspond to the second set of automated data. For example, a system for reading a data storage medium can include a computer comprising a central processing unit ("CPU"), a functional memory which can be, for example, RAM (random access memory) or "memory". "core", mass storage memory (such as one or more disk drives or CD-ROM drives), one or more display devices (eg, cathode ray tube ("CRT") displays, diode displays that emit light ("LED"), liquid crystal displays ("LCDs"), electroluminescent screens, fluorescent vacuum screens, field emission screens ("the EDFs"), plasma screens, projection panels, etc.) , one or more user input units (eg, boards, microphones, mice, touch screen, etc.), one or more input lines, and one or more output lines, all of which are interconnected by a bus conventional bi-directional system. The system can be a stand-alone computer, or it can be connected in the network (for example, through local area networks, wide coverage networks, intranets, extranets, or the Internet) or other systems (for example, computers, computers, servers, etc.). The system may also include additional controlled units of computers such as electronics and devices for users. Input hardware can be attached to the computer by input lines and can be implemented in a variety of ways. The automated data of this invention can be typed through the use of a modem or modems connected by one. telephone line or a dedicated data line. Alternatively or additionally, the input hardware may comprise CD-ROM drives or disk drives. Along with a deployment terminal, a keyboard can also be used as an input unit. The output hardware can be coupled to the computer by output lines and can similarly be implemented by conventional devices. By way of example, the output hardware may include a display unit for displaying a graphic representation of a link cavity of this invention using a program such as QUANTA as described herein. The output hardware could also include a printer, so that the output of the hard copy can be produced, or a disk drives to store the output of the system by the end user. In the operation, a CPU coordinates the use of the various input and output units, coordinates data access from the mass storage devices, access to and from the functional memory, and determines the sequence of the stages of data processing. A number of programs can be used to process the automated data of this invention. Such programs are discussed in reference to the computational methods of drug discovery as described herein. References to the components of the hardware system are included as appropriate throughout the description of the data storage medium. Automated storage devices useful in the present invention include, but are not limited to, magnetic devices, electronic devices, optical devices and combinations thereof. Examples of such data storage devices include, but are not limited to, hard disk devices, CD devices, digital video disk devices, flexible disk devices, removable hard disk devices, magneto-optical disk devices, devices. of magnetic tapes, instant memory devices, bubble memory devices, holographic storage devices, and any other peripheral mass storage device. It should be understood that these storage devices include necessary hardware (for example, disk drives, controllers, sources of supply, etc.), as well as any necessary means (for example, disks, flash cards, etc.), to allow the storage of data. G. Pharmaceutical Compositions The present invention contemplates methods for treating certain diseases in a mammal, preferably a human, in need of such treatment using the ligands, and preferably the inhibitors, as described herein.

The ligand can be advantageously formulated into pharmaceutical compositions comprising a therapeutically effective amount of the ligand, a pharmaceutically acceptable carrier and other compatible ingredients, such as adjuvants, Freund's complete or incomplete adjuvant, suitable for formulating such pharmaceutical compositions as known to those skilled in the art. experts in the art. Pharmaceutical compositions containing the ligand can be used for the treatment of a variety of psychotic disorders and tai condition such as schizophrenia, illusory disorders and drug-induced psychosis; anxiety disorders such as panic and obsessive-compulsive disorder; and movement disorders including Parkinson's disease and Huntington's disease. Examples of psychotic disorders that may be treated in accordance with the present invention include, but are not limited to, schizophrenia, for example, of the paranoid, disorganized, catatonic, undifferentiated or residual type; schizophreniform disorder; schizoaffective disorder; for example, of the illusory type or of the depressive type; illusory disorder; Substance-induced psychotic disorder, eg psychosis induced by alcohol, amphetamine, marijuana, ***e, hallucinogens, inhalants, opioids or phencyclidine; personality disorder of the paranoid type; and personality disorder of the schizoid type. Examples of movement disorders that can be treated in accordance with the present invention include, but are not limited to, those selected from Huntington's disease and dyskinesia associated with dopamine agonist therapy, Parkinson's disease, restless legs syndrome, and essential tremor. . Other disorders that can be treated according to the present invention are obsessive / compulsive disorders, Tourette's syndrome and other tic disorders. The pharmaceutical composition is administered to the mammal in a therapeutically effective amount so that the treatment of the disease occurs. The present invention is further illustrated by the following examples, which would not be construed as limiting in any way. The contents of all cited references (including literature references, issued patents, published patent applications as cited throughout this application) are therefore expressly incorporated for reference in their entireties. The practice of the present invention will employ, unless otherwise indicated, conventional techniques of cell biology, cell culture, molecular biology, microbiology and recombinant DNA, X-ray crystallography and molecular modeling which are within the capability of the art. . Such techniques are fully explained in the literature. See, for example, Molecular Cloning: A Laboratory Manual, 2nd Ed., Ed. by Sambrook, Fritsch and Maniatis (Cold Spring Harbor Laboratory Press: 1989); DNA Cloning, Volumes I and II (D. N. Glover ed., 1985); Oligonucleotide Synthesis (M. J. Gait ed., 1984); Mullis et al. U.S. Patent No: 4,683, 195; Nucleic Acid Hybridization (B. D. Hames &S. J. Higgins eds, 1984); Transcription and Translation (B. D. Hames &S. Higgins, eds., 1984); B. Perbal, A Practical Guide to Molecular Cloning (1984); the treatise, Methods In Enzymology (Academic Press, Inc., N.Y.); Methods In Enzymology, Vols. 154 and 155 (Wu et al., Eds.), Crystallography Made Clear: A Guide for Users of Macromolecular Models (Wales Rhodes, 2nd Ed. San Diego: Academic Press, 2000).

EXAMPLES Example 1: Construction and expression of the wild-type catalytic domain of PDE10A tagged with Hisd. Amino acids 442-774 of wild-type PDE10A from rattus norvegicus (rat) (SEQ ID NO: 1) were subcloned into a pFastBac-1 in order to generate recombinant baculovirus using the Bac-to-Bac system ( Gibco Carlsbad, CA), which corresponds to the amino acids in the SEC. FROM IDENT. NO .: 2. The modified fusion protein was expressed in SF21, as a version labeled with His, with amino acids 2-7 of the SEC. FROM IDENT. NO .: 2, being the HIS tag portion, and amino acids 20-362 of SEC. FROM IDENT. NO .: 2 (Thr442 to Asp774 of SEQ ID NO: 1), being the catalytic region of the rat PDE10A protein portion. Insect cells were infected with the recombinant baculovirus at an MOI (multiplicity of infection) of 0.5 and harvested for 72 hours after infection. The granules of infected cells were frozen at -80 ° C to transfer to. purification. Example 2. Purification of the catalytic domain of the wild-type PDE10A tagged with Hisd. The baculovirus cell paste (80 g) containing the recombinant protein N3C3 from over-expressed PDE10a was resuspended in a 6-volume buffer A (~ 430 ml), containing 50 mM HEPES (4- (2- hydroxyethyl) -1-piperazinetanesulfonic acid) pH 7.5, 300 mM NaCl (sodium chloride), 3% (v / v) glycerol, 0.1 mM TCEP (tri (2-carboxyethyl) phosphine hydrochloride) and cocktail inhibitor tablets of Protease Complete ™ (Roche). The cells were used with a passage in a microfluidizer and cell debris was removed by centrifugation at 4 ° C for 45 minutes at 14,000 rpm in a Sorval SLA-1500 rotor. The supernatant was transferred to a clean tube and 10 ml of a Metal HEEL Affinity Resin (BD-Clonetech) was added. The suspension was incubated with gentle rolling at 4 ° C for 1 hour and then subjected to centrifugation at 700 x g in a rocking-pan rotor. The supernatant was discharged and the resin resuspended in 20 ml of buffer A and transferred to an XK-16 column (Pharmacia Skokie, Illinois) connected to an FPLC ™. The resin was washed with 5 column volumes of buffer A. After the washing step, the column containing the bound resin was connected upstream to a Fast Desalt XK-26/30 column (Pharmacia) previously equilibrated with buffer A. PDE10A N3C2 was eluted from the HEPA resin with a step gradient of buffer A + 120 mM imidazole. The eluted fractions were exchanged with buffer in buffer B containing 25 mM HEPES pH 7.5, 50 mM NaCl, 0.1 mM TCEP, 10 μM E64 (rasp-Epoxysuccinyl-L-leucylamido (4-guanidino) butane N- (trans -epoxysuccinyl) -L-leucine 4-guanidinobutylamide L-uraps-3-carboxyoxyran-2-carbonyl-L-leucylagmatin), 1 mM PMFS (phenylmethylsulfonyl fluoride), 1 μg / ml ieupeptin and loaded onto a monoS column (Pharmacia). The protein was eluted with a gradient from 0-500 mM NaCl over 40 column volumes in buffer B. The eluted fraction was concentrated to 1.0 ml and loaded onto a predex grade Superdex 75 HiLoad 16/60 column (Pharmacia ) equilibrated with buffer C containing 25 mM HEPES pH 7.5, 150 mM NaCl, 1 mM TCEP, 10 μl E64, 1 mM PMSF, 1 μg / ml leupeptin. The protein eluted between 60 - 70 ml. The eluted fraction was concentrated to 5.7 mg / ml. Example 3: Crystallization of the wild type catalytic domain of PDE10A with the compound of Formula 1 (6,7-dimethoxy-4- [8- (4-methyl-piperazine-1-sulfonyl) -3,4-dihydro-1 H-isoquinolin-2-yl] -quinazoline) The crystallization sieves were prepared using the droplet / vapor diffusion method in Greiner 96-well plate sitting. The protein was mixed 2: 1 with the compound of Formula 1 (6,7-d-methoxy-4- [8- (4-methyl I-pipe razin-1-sulph onyl) -3,4-dihydro-1 H-isoquinolin-2-yl] -quinazoline). The conditions were selected using Hampton Research Crystal Screen HT and Emerald Biosciences Wizard I and II sieves. The crystals were obtained under condition B5 of the Crystal Screen HT containing 15% PEG-4000, 0.05 M Tris pH 8.5, 0.1 M lithium sulfate. The optimization of this condition using the suspension droplet / vapor diffusion method in 24-well VDX plates produced crystals measuring 0.23 x 0.25 x 0.05 mm with well conditions containing 20% PEG-4000 (? Olietilenglicol-4000) ), 0.1 M Tris pH 8.5, 0.2 M of ammonium sulfate. Example 4: Collection of X-ray data, determination of structure and refinement of PDE10A: compound of the complex of Formula 1 (6,7-dimethoxy-4- [8- (4-methyl-piperazine-1-sulfonyl] 3, 4-dihydro-1 H-isoquinolin-2-yl] -quinazoline.) The preferred crystals in Example 3 were transferred to a cryoprotective solution, made from the receptor solution, with 15% ethylene glycol, and then frozen immediately in a cold nitrogen gas stream at 100K.A total data set was collected from a crystal frozen in this way in a Rigaku RAXIs lie detector, mounted on a Rigaku RU-200 generator with Osmic optics. HKL software set (Otwinowski, Z. & Minor, W. Methods Enzymology 276, 307-326 (1997). The data collection statistics are summarized in Table 5a. The crystals belong to a spatial group R3 with unit cell dimensions a = 120.6, b = 120.6, c = 82.1 A, a = b = 90.0, g = 120 °. These contain 1 molecule of the polypeptide, and one molecule of the inhibitor per asymmetric unit. The structure was solved by the molecular replacement method, using the AMORE program (Navaza, J., Acta Cryst., 157-163 (1994)). A homology model of PDE10, based on the previously determined structure of PDE5 was used as the search model. A clear solution to the search for rotation / translation was found, with a starting R factor of 47.8% for the data at 2.5 A. The final model was constructed with a combination of automatic adjustment in the ArpWarp program (http: // www. .arp-warp.org) and manual reconstruction on the graphics screen, using the program O Refinement in Refmac was carried out using all the data in the resolution range. 30.0-1.8 A. The factors of partial structure from a solvent model in volume and the correction of anisotropic factor B were supplied throughout the refinement. The R factor of the current model is 0.22 (free R factor, 7% of the data, 0. 27). The refinement statistics are summarized in Table 5b. The current model contains 307 to 352 amino acid residues calculated at the base of the construct. The interpretable electron density is observed for all residues from 454-760. Residues 442-453 in the N term and 761 to 774 have not been modeled. In addition, the model contains a Zn2 + ion, a Mg2 + ion, an inhibitor molecule, the compound of Formula 1 (6,7-dimethoxy-4- [8- (4-methyl-piperazine-1-sulfonyl ) -3,4-dihydro-1 H-isoquinolin-2-yl] -quinazoline) and 312 water molecules. A schematic representation of 6,7-dimethoxy-4- [8- (4-methyl-piperazin-1-sulfonyl) -3,4-dihydro-1H-isoquinolin-2-yl] -quinazoline is given below.

Formula 1 6,7-dimethoxy-4- [8- [4-methyl-piperazin-1-sulfonyl) -3,4-dihydro-1 H -isoquinolin-2-yl] -quinazoline. The mass spectrum m / e calculated for M + H = 484.6 Found 484.2. The compound of Formula I is described in the Application Provisional Record of the United States, pending, filed on February 18, 2004, entitled "Tetrahydroisoquinolinyl Derivatives Of Quinazoline And Isoquinoline "and is incorporated herein by reference in its entirety.

Table 5a - Data Statistics Numbers in parentheses refers to the highest resolution range (1.80-1.86A) 2Rsym =? (| - < | >) /? < | > Table 5b - Refinement statistics 3D _ R -? | J F0bs | - / f | Fcalc ||? | Fobs |

Claims (20)

1. CLAIMS 1. A crystal of phosphodiesterase 10A (PDE10A). 2. The PDE10A crystal according to claim 1, characterized in that it is derived from a mammal. 3. The PDE10A crystal according to claim 2, characterized in that the mammal is a rat. 4. A crystal of the catalytic domain of PDE10A. 5. The crystal according to claim 4, characterized in that it has a spatial group of R3 so as to form a unitary cell of dimensions of approximately a = b = 120.56A, and c = 82.23 A. 6. A crystal of the catalytic domain of PDE10A, characterized in that the catalytic domain has a three-dimensional structure characterized by the atomic structure coordinates of Figure 4. 7. The PDE10A crystal, characterized in that it comprises SEC. FROM IDENT. NO .: 2, or a counterpart, analog or variant thereof. 8. A crystal of a ligand complex PDE10A / PDE10A. 9. The crystal complex according to claim 8, characterized in that the ligand is an antagonist or an inhibitor. 10. The crystal complex is characterized in that it comprises a polypeptide with an amino acid sequence spanning amino acids Thr442 to Asp774 listed in SEQ. FROM IDENT. NO .: 1, or a counterpart, analog or variant thereof. The crystal complex according to claim 10, characterized in that the homologue or variant has an amino acid identity of at least 98%, 95% or 90% with a polypeptide having an amino acid sequence spanning amino acids Thr442 to Asp774 listed in the SEC. FROM IDENT. NO .: 1. The crystal complex according to claim 11, characterized in that the crystal comprises the atomic coordinates listed in FIGURE 4. 13. The crystal complex according to claim 10, characterized in that the homolog or variant thereof has a protein structure comprising the atomic coordinates, or portions thereof, that are within an average root of squares of +/- 1.5, 1.2, 1.0, 0.7, 0.5 or even 0.
2. 2 A of the atomic coordinates , or portions thereof listed in FIGURE 4. 14. A polypeptide, characterized in that it comprises the amino acid sequence set forth in SEQ. FROM IDENT. NO .: 1 or a homologue, or variant thereof, wherein the molecules are arranged in a crystalline manner in a spatial group of R3 so as to form a unit cell of dimensions a = b = 120.56 A and c = 82.23 A, and which effectively diffracts X-rays for the determination of the atomic coordinates of the PDE10A polypeptide at a resolution of approximately 1.8 A. 15. A crystal of a protein-ligand molecule or molecular complex, characterized in that it comprises: (a) a polypeptide with a amino acid sequence from Thr442 to Asp774 listed in SEC. FROM IDENT. NO .: 1, or a homologue or a variant thereof; (b) a ligand; (c) and the crystal effectively diffracts X-rays for the determination of atomic coordinates of the protein-ligand complex at a resolution of more than 1.8 Angstroms. 16. The crystal according to claim 15, characterized in that it has a spatial group of R3 so as to form a unitary cell of dimensions a = b = 120.56 A and c = 82.23 A. 17. The crystal according to claim 15, characterized in that it has a three-dimensional structure characterized by the atomic coordinates of Figure 4. 18. The PDE10A crystal according to claim 1, characterized in that it has atomic coordinates established in FIGURE 4. 19. A method for generating the atomic coordinates of 3-D of the PDE10A protein homologs using the X-ray coordinates of PDE10A described in FIGURE 4, comprising: identifying the sequences of one or more proteins which are homologous with PDE10A; align the homologous sequences with the sequence of PDE10A (SEQ ID NO: 1); identify structurally conserved and structurally variable regions between the homologous sequences, and PDE10A (SEQ ID NO: 1); generate 3-D coordinates for structurally conserved residues, variable regions and side chains of the homologous sequences from those of PDE10A; and combining the 3-D coordinates of the conserved residues, variable regions and side chain conformations to generate total or partial 3-D coordinates for such homologous sequences. 20. A method for identifying potential ligands for PDE10A, or homologs, analogs or variants thereof, characterized in that it comprises: exhibiting a three-dimensional structure of a PDE10A enzyme, or portions thereof, as defined by the atomic coordinates in FIGURE 4, or a computer screen; optionally replacing one or more amino acid residues of the PDE10A enzyme listed in SEQ. FROM IDENT. NO .: 1, or one or more of the amino acids listed in Tables 1-4, or one or more amino acid residues selected from Leu625, Phe629, Val668, Phe686, Met703, Gln716 and Phe719, in such three-dimensional structure with a different amino acid of natural origin or a non-natural amino acid; employing such a three-dimensional structure to design or select the ligand; contacting the ligand with PDE10A, or variant thereof, in the presence of one or more substrates, and measuring the ability of such a ligand to modulate the activity of PDE10A.