CN109536465B

CN109536465B - Composition for screening antituberculosis drugs, screening model and screening method

Info

Publication number: CN109536465B
Application number: CN201710858802.XA
Authority: CN
Inventors: 肖春玲; 蒙建州; 刘忆霜; 邓琪; 关艳; 王冕; 韩江雪; 李东升
Original assignee: Institute of Medicinal Biotechnology of CAMS
Current assignee: Institute of Medicinal Biotechnology of CAMS
Priority date: 2017-09-21
Filing date: 2017-09-21
Publication date: 2020-11-13
Anticipated expiration: 2037-09-21
Also published as: CN109536465A

Abstract

The invention provides a composition for screening antituberculosis drugs, a screening model and a screening method. Specifically, the invention provides a method for heterologous expression of Aspartate Semialdehyde Dehydrogenase (ASD), which comprises the following steps: (1) transferring a strain containing pET28a (+): asd expression plasmid into a culture medium containing Km and an agent for increasing cell osmotic pressure, and culturing to obtain a transfer culture, wherein the concentration of the agent for increasing cell osmotic pressure is 500-1000 mM; (2) adding IPTG (isopropyl thiogalactoside) into the transfer culture, and culturing at 20-23 ℃ to obtain bacterial cells expressing ASD, wherein the final concentration of IPTG is 5-20 mu M (preferably 10-15 mu M); (3) and (3) collecting the bacterial cells obtained in the step (2), and cracking to obtain the ASD. The invention also provides a composition, a screening model and a screening method for screening the antituberculosis drugs containing the ASD, and the antituberculosis drugs can be screened rapidly, economically and in high throughput.

Description

Composition for screening antituberculosis drugs, screening model and screening method

Technical Field

The invention relates to the field of medicines, in particular to a composition for screening antituberculosis drugs, a screening model and a screening method.

Background

The anti-tuberculosis drugs such as rifampin (rifampin), isoniazid (isoniazid), ethambutol (ethambutol) and the like are widely applied, and the death rate of tuberculosis is greatly reduced. However, with the long-term use of these antitubercular drugs and the improper or irregular administration of these drugs, Single Drug Resistant (SDR), Multi Drug Resistant (MDR) and even extensively resistant (XDR) Mycobacterium Tuberculosis (MTB) has emerged. The statistical data show that: 3.7% of patients with newly infected tuberculosis are MDR-TB infected patients, the MDR-TB carrying rate in retreated patients is up to 20%, and the XDR-TB patients in MDR-TB patients are more up to 9.0%. The continuous generation and spread of drug-resistant MTB reduce the cure rate of tuberculosis, and the mortality rate of tuberculosis patients infected with MDR and XDR MTB is greatly improved. Therefore, the appearance and spread of the drug-resistant MTB enable tuberculosis to become a serious infectious disease threatening human health again, and the development of novel drugs for resisting the drug-resistant MTB is urgent.

The research and development of antituberculosis drugs has become a global research hotspot, but the research progress of novel antituberculosis drugs is extremely slow, and the clinical requirement for treating drug-resistant tuberculosis cannot be met, so that clinical experts have a call that tuberculosis is not available for treatment. The lack of new targets available for drug development is a major cause of hindering the development process of anti-tuberculosis drugs, and the lack of targets becomes a bottleneck in the development of anti-tuberculosis drugs. Only limited targets for developing antituberculosis drugs include InhA, EmbAB, DNA gyrase, RNA polymerase and the like, and antituberculosis drugs developed based on these targets are widely used for clinical treatment of tuberculosis. Strains resistant to these drugs are also emerging due to mutations in the target genes. Bedaquiline and Delamanid are only 2 antituberculosis drugs which are successfully developed in the last 50 years, have good inhibition effect on sensitive MTB and drug-resistant MTB, and can effectively treat tuberculosis caused by drug-resistant MTB. They have the common feature that the action mechanism is different from that of the traditional antituberculosis drugs, and the action site is a brand new drug target.

Aspartate-semialdehyde dehydrogenase (ASD) is the second enzyme in the metabolic pathway of Mycobacterium tuberculosis aspartate, and bioinformatics analysis indicates that the enzyme gene is an essential gene for MTB. Physiological studies on the constructed asd-conditioned mutant of MTB revealed that down-regulation of asd expression affected MTB proliferation, that cell wall synthesis was blocked, thereby disrupting the normal long-rod structure of the cells, and that MTB, which did not have a complete cellular structure, also had a disrupted ability to infect macrophages. Researches show that the expression of asd is very important for maintaining the normal physiological function of MTB and is a potential antituberculous drug target.

According to the characteristic of ASD catalytic reversibility, early researchers established ASD inhibitor screening models of Streptococcus pneumoniae, Vibrio cholerae, Candida albicans and Escherichia coli by taking aspartic acid semialdehyde, NADP and phosphoric acid as substrates. However, since the substrate aspartic semialdehyde is unstable and is easily oxidized to aspartic acid, there is no report on commercially available aspartic semialdehyde.

Although ASD from MTB was reported to be expressed in 2005, we were unable to obtain sufficient quantities of active enzyme according to the relevant methods. We found that the expression of MTB ASD is mainly an inclusion body by exploring the influence of expression vectors, host bacteria, fusion expression, secretion expression and other modes on the expression of MTB ASD, and that even the ASD with very little soluble content is obtained, no enzyme activity is detected. Little progress has been found in the last decade of research on MTB ASD literature, and screening of MTB ASD inhibitors has been reported only in 2015 using in silico virtual screening. The possible reason is also the difficulty in breaking the bottleneck of MTB ASD expression.

Disclosure of Invention

The present inventors have surprisingly found, through a great deal of creative work, that a large amount of soluble and enzymatically active ASD can be stably obtained by controlling the temperature, the osmotic pressure inside and outside the cell membrane, and using a low concentration of an inducer. On the basis, escherichia coli type III aspartokinase (Lys C) is used for catalyzing aspartic phosphorylation to provide a substrate for ASD, so that an antituberculosis drug screening model is established.

Accordingly, in a first aspect the present invention provides a method for the heterologous expression of Aspartate Semialdehyde Dehydrogenase (ASD), comprising the steps of:

(1) a strain containing pET28a (+): asd expression plasmid is transferred to a medium containing Km and an agent for increasing cell osmotic pressure at a concentration of 500mM or 1000mM (e.g., 500mM or 600mM or 700mM or 800mM or 900mM or 1000mM) to obtain a transfer culture;

(2) adding IPTG to the transfer culture, and culturing at 20-23 deg.C (such as 20 deg.C, 21 deg.C, 22 deg.C or 23 deg.C) to obtain ASD-expressing somatic cells, wherein the final concentration of IPTG is 5-20 μ M (preferably 10-15 μ M, such as 5 μ M, 10 μ M, 15 μ M or 20 μ M);

(3) and (3) collecting the bacterial cells obtained in the step (2), and cracking to obtain the ASD.

In some preferred embodiments, the method is characterized by one or more of the following:

a. the strain in the step (1) is Escherichia coli BL21ATAR^TM(DE3) strain;

b. the Km concentration in the step (1) is 100 mu g/mL;

c. the ASD expressing strain in step (1) is inoculated in an amount of 2-10% (e.g., 2%, 2.5%, 3%, 3.5%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%);

d. the culture conditions of the transfer culture obtained in the step (1) are as follows: culturing at 37 ℃. + -. 2 ℃ and 150-;

e. the agent for increasing the cell osmotic pressure in the step (1) is selected from the group consisting of cyclized alpha-1, 4-glucan, cyclodextrine and sorbitol;

f. the culture medium in the step (1) is an LB culture medium;

g. in the step (1), before the transfer, the method further comprises the step of carrying out amplification culture on the strain; preferably, the expanding culture refers to culturing the strain on LB medium containing 100. mu.g/mL Km at 37 ℃ and 200rpm for 8-16h (e.g., 8h, 10h, 12h, 14h or 16h) or until the bacteria are in logarithmic growth phase;

h. the culture conditions of the ASD-expressing bacterial cells obtained in the step (2) are as follows: 150-200rpm (e.g., 150rpm, 160rpm, 170rpm, 180rpm, 190rpm, or 200rpm), 8-24h (e.g., 8h, 10h, 12h, 14h, 16h, 18h, 20h, 22h, or 24 h;

i. in the step (3), after cracking, a purification step is further included; preferably, column chromatography is used for purification; further preferably, after purification, a desalting step is further included.

In some preferred embodiments, the concentration of the agent that increases the osmotic pressure of a cell is in the range of 500mM to 1000 mM. In this case, the expressed protein was soluble, no inclusion bodies appeared, inclusion bodies appeared below 500mM, and the lower the concentration, the larger the inclusion bodies. However, when the medium does not contain an agent for increasing the cell osmotic pressure, a soluble protein is hardly obtained.

In some preferred embodiments, the temperature of the cell culture in step (2) is between 20 ℃ and 23 ℃. Inclusion bodies can appear at the temperature higher than 23 ℃, the activity of the strain at the temperature lower than 20 ℃ is damaged, and the capability of expressing protein is reduced, even the target protein cannot be expressed.

In some preferred embodiments, a low concentration of inducer may be added. For example, low concentrations of IPTG favor expression of the target protein. The present inventors have searched for expression of protein at IPTG 0, 5, 10, 15, and 20. mu.M, preferably at IPTG concentration of 10-15. mu.M.

In some preferred embodiments, the target protein is well expressed in LB medium containing 500-1000mM high osmotic solution under IPTG induction at 5-20. mu.M (preferably 10-15. mu.M) at low temperature of 20-23 ℃.

In some preferred embodiments, the strain containing pET28a (+): asd expression plasmid can be obtained by genetic engineering methods. Specifically, a pET28a (+): asd expression plasmid can be obtained using PCR technology and then transformed into a host cell to obtain a strain containing pET28a (+): asd expression plasmid.

In some preferred embodiments, the pET28a (+): asd expression plasmid refers to a plasmid obtained by the method of step (1) of example 1 of the present invention.

In another aspect, the present invention provides a composition for screening antitubercular agents, which contains ASK (LysC), ASD, ATP, aspartic acid, NADPH, Tris-HCl, MgCl, etc. type III of Escherichia coli₂And DTT;

wherein the ASD is obtained by the method of the first aspect of the invention.

In some preferred embodiments, the composition is characterized by one or more of the following:

a content of LysC is 0.5-2U (e.g., 1U);

asd content of 0.2-0.5U (e.g. 0.2U);

a final concentration of ATP of 0.5-5mM (e.g., 1 mM);

d. aspartic acid to a final concentration of 1-10mM (e.g., 5 mM);

final concentration of nadph 0.5 mM;

final concentration of Tris-HCl 20-100mM (e.g., 50 mM);

g.MgCl₂the final concentration of (A) is below 20 mM;

a final concentration of DTT of 0.5-5mM (e.g., 1 mM);

i. the pH of the composition is 7.8-9.0 (e.g., 8.0).

In another aspect, the present invention provides a screening model for antitubercular drugs, which comprises 1) a screening model consisting of LysC, ASD, ATP, aspartic acid, NADPH, Tris-HCl, MgCl₂And DTT; 2) prepared from LysC, ASD (inactivated), ATP, aspartic acid, NADPH, Tris-HCl, MgCl₂And DTT; and 3) from LysC, ASD, ATP, aspartic acid, NADPH, Tris-HCl, MgCl₂A sample group consisting of DTT and a compound to be tested;

wherein the ASD is obtained by the method of the first aspect of the invention.

In some of the preferred embodiments, the first and second,

the concentration or content of each component in the positive control group is respectively LysC 1U, ASD 0.2.2 0.2U, ATP 1mM, aspartic acid 5mM, NADPH 0.5mM, Tris-HCl 50mM, MgCl₂ 5mM、DTT 1mM；

The concentration or the content of each component in the negative control group is respectively as follows: LysC 1U, ASD (inactivated) 0.2U, ATP 1mM, aspartic acid 5mM, NADPH 0.5mM, Tris-HCl 50mM, MgCl₂ 5mM、DTT 1mM；

The concentration or content of each component in the sample group is respectively as follows: LysC 1U, ASD 0.2U, ATP 1mM, aspartic acid 5mM, NADPH 0.5mM, Tris-HCl50mM、MgCl₂5mM, DTT 1mM, and 20 μ g/mL of the test compound;

in each group, 1. mu.L DMSO was added, and the final volume of each group was 100. mu.L.

In some preferred embodiments, the ASD may be inactivated by incubation at 90 ℃ for 30 min.

In another aspect, the present invention provides a method for screening an anti-tuberculosis drug using the model, which comprises the steps of:

1) reacting the positive control group, the negative control group and the sample group at 37 ℃ for 15-30 minutes;

2) measuring the light absorption intensity of each group at 340nm after reaction, and screening compounds with ASD activity inhibition rate of more than 30% to obtain candidate drugs;

the ASD activity inhibition rate calculation formula is as follows:

wherein An is the light absorption value of the positive control group, As is the light absorption value of the sample group, and Ap is the light absorption value of the negative control group.

In some preferred embodiments, the method further comprises the step of rescreening; preferably, the rescreening means: and testing the inhibitory activity of the candidate drug on mycobacterium tuberculosis in vitro, and screening to obtain the compound with the anti-tuberculosis activity.

In another aspect, the invention provides the use of said composition for high throughput screening of anti-tuberculosis drugs in vitro.

In another aspect, the invention provides the use of said model for high throughput screening of anti-tuberculosis drugs in vitro.

Advantageous effects of the invention

The present inventors have stably obtained a large amount of soluble and enzymatically active ASD by controlling the temperature, the osmotic pressure inside and outside the cell membrane, and using a low concentration of an inducer. On the basis, the Escherichia coli III type aspartokinase (Lys C) is used for catalyzing aspartic acid phosphorylation to provide a substrate for ASD, so that an antituberculous drug screening model is established, and the antituberculous drug can be screened quickly, economically and in high throughput for an antituberculous drug target by the ASD.

Drawings

FIG. 1 is a standard curve for quantitative determination of the ASD concentration obtained in example 2 using the BCA protein assay.

FIG. 2 shows ASD purification by SDS-PAGE power supply, wherein the first trace is a pre-stained protein marker; the second way is to express the whole protein of the strain; the third step is precipitation; the fourth step is supernatant fluid; the fifth passage is flow-through liquid; the sixth lane is the ASD.

FIG. 3 shows the purification of LysC detected by SDS-PAGE power supply, wherein LysC is shown in the first trace; the second passage is flow-through liquid; the third step is precipitation; the fourth step is supernatant fluid; the fifth way is to express the whole protein of the strain; the sixth lane is a prestained protein marker.

Detailed Description

Embodiments of the present invention will be described in detail below with reference to examples, but those skilled in the art will appreciate that the following examples are only illustrative of the present invention and should not be construed as limiting the scope of the present invention. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products commercially available.

EXAMPLE 1 cloning and expression of recombinant aspartate semialdehyde dehydrogenase ASD

(1) Cloning of asd Gene and construction of expression vector

Primers were designed based on the NCBI published ASD gene sequence (GenBank accession number 9885118): asdh F (5' -TTTTGAATTCATGGGCCTGTCAATAGGGATC-3 ') and asdh R (5' AAAA)AAGCTTTCACAAGTCGGCGGTCAGC) was used to amplify the ASD gene using the MTB genome as a template. Underlined are EcoR I and Hind III restriction sites. The reaction system is as follows:

PCR SuperMix was purchased from Beijing Quanjin Biotechnology Ltd, and primers were synthesized from Beijing Huada. The reaction procedure is as follows:

the PCR product was purified using a gel recovery kit (Beijing Panzhijin Biotechnology Co., Ltd.), the purified product and the plasmid pET28a (+) were digested with EcoR I and Hind III (Dalian TaKaRa Co., Ltd.), respectively, and the digested fragments were heat-inactivated and incubated with T4DNA ligase (Dalian TaKaRa Co., Ltd.) at 16 ℃ for 16 hours. The ligation solution was transformed into E.coli DH 5. alpha. competent cells, LB solid plates containing 100. mu.g/mL Km were plated with the transformation solution, and transformants were selected for sequencing verification to obtain plasmid pET28a (+): asd.

(2) Construction of E.coli containing expression plasmid

Transformation of the plasmid pET28a (+): asd into E.coli BL21STAR^TM(DE3) an ASD-expressing strain was obtained and stored at-80 ℃ until use.

(3) Inducible expression of ASD

The preserved E.coli BL21STAR containing the expression plasmid pET28a (+): asd^TM(DE3) was streaked onto LB solid plates containing 100. mu.g/mL Km and cultured overnight at 37 ℃ by inversion. A single colony was inoculated into 20mL of liquid LB medium containing 100. mu.g/mL Km and cultured overnight at 37 ℃ at 200 rpm. The overnight culture was transferred at a rate of 2.5% to 200mL of liquid LB medium (containing 500mM cyclized. alpha. -1, 4-glucan) containing 100. mu.g/mL Km, and cultured at 37 ℃ and 200rpm until the OD600 was about 0.6. To 200mL of the transfer culture, 1M IPTG was added to a final concentration of 20. mu.M, at 20 ℃ and 200rpm, and the culture was carried out for 24 hours. The cells were collected and washed 3 times with lysis buffer.

Example 2 purification of recombinant aspartate semialdehyde dehydrogenase

Cell disruption: suspending the collected cells in lysis buffer (20mM Tris-HCl, 500mM NaCl, 10mM imidazole, 1mM DTT, pH 8.0) to 50mg/mL of a bacterial solution; disrupting the cells three times at a pressure of 800bar using a pressure disruptor pre-cooled to-15 ℃; the cell suspension was centrifuged at 10000g for 20min to remove insoluble matter, and then filtered through a 0.45 μm filter.

Protein purification: by using

The explorer system performs protein purification work using 1mL pre-packed HiTrappscaling HP as purification medium.

Elution was carried out with a buffer containing 20mM Tris-HCl, 500mM NaCl, 400mM imidazole and 1mM DTT, pH 8.0, according to the following procedure:

the concentration of the eluent is 0-100%, the elution time is 10min, the collection volume is set to be 1mL, and the purification effect is detected by SDS-PAGE.

Protein desalting: about 2.5mL of the protein sample after purification elution (diluted to an integral multiple of 2.5 for desalting in multiple times when the total volume of elution is more than 2.5 mL) was added to the desalting column PD 10. 3.5mL of desalting buffer (20mM TrisHCl, 20mM NaCl, 2.0mM DTT, pH 8.0) was added and collected.

10.5mL of desalted sample is obtained by 1L of fermentation liquor, the desalted solution is added with glycerol with the same volume as the desalted solution, mixed uniformly, subpackaged in 1.5mL of EP tubes and stored at minus 80 ℃.

Protein quantification:

a standard curve was prepared according to the procedure of Easy II Protein Quantitative Kit (BCA) (product number: DQ111-01, Beijing Quanjin Biotechnology Co., Ltd.) and the Protein concentration of the ASD after desalting was measured, as shown in FIG. 1.

The light absorption value (average value) of the diluted ASD was substituted into the formula, and the protein concentration was calculated to be 3.66. mu.g/. mu.L, i.e., 3.66mg/mL, and the amount of ASD obtained was calculated to be 384.3mg/L based on the dilution factor (10) and the total amount (10.5mL) of the protein.

SDS-PAGE electrophoretic analysis:

sample treatment: mu.L of sample was taken, 20. mu.L of 5 Xloading buffer was added, and boiled in boiling water for 10 min.

Preparing glue:

8% separation gel:

3.9% concentrated gum:

electrophoresis: electrophoresis was performed at a constant voltage of 80V for about 0.5h, after which 120V was used until the bromophenol blue base line ran to the edge of the glass plate.

Dyeing and decoloring: after electrophoresis, the PAGE gel was immersed in a dish containing a staining solution and stained with gentle shaking at 80rpm for 2 h. And (3) recovering the dyeing liquid, slightly washing the glue twice by using tap water, adding the decoloring liquid into the plate, slowly shaking for decoloring, and replacing the decoloring liquid for 3-4 times in the middle. The results of the experiment were recorded using a gel imager camera, as detailed in figure 2.

Example 3 expression and purification of recombinant E.coli type III ASK (Lys C)

(1) Cloning of LysC Gene and construction of expression vector

Primers were designed based on the LysC gene sequence published by NCBI (GenBank accession number 948531): lysC F (5' -TTTT)GAATTCATGTCTGAAATTGTTGTCT-3 ') and lysC R (5' -AAAA)AAGCTTTTACTCAAACAAATTACTA-3') was used to amplify the LysC gene using the E.coli genome as a template. Underlined are EcoR I and Hind III restriction sites. The reaction system is as follows:

the PCR product was purified using a gel recovery kit (Beijing Panzhijin Biotechnology Co., Ltd.), the purified product and the plasmid pET28a (+) were digested with EcoR I and Hind III (Dalian TaKaRa Co., Ltd.), respectively, and the digested fragments were heat-inactivated and incubated with T4DNA ligase (Dalian TaKaRa Co., Ltd.) at 16 ℃ for 16 hours. The ligation solution was transformed into E.coli DH 5. alpha. competent cells, LB solid plates containing 100. mu.g/mL Km were plated with the transformation solution, and transformants were selected for sequencing verification to obtain plasmid pET28a (+): lysC.

(2) Construction of E.coli containing expression plasmid

Transformation of the plasmid pET28a (+): lysC into E.coli BL21STAR^TM(DE3) the LysC-expressing strain was obtained and stored at-80 ℃ until use.

(3) Inducible expression of LysC

The preserved E.coli BL21STAR containing the expression plasmid pET28a (+): asd^TM(DE3) was streaked onto LB solid plates containing 100. mu.g/mL Km and cultured overnight at 37 ℃ by inversion. A single colony was inoculated into 20mL of liquid LB medium containing 100. mu.g/mL Km and cultured overnight at 37 ℃ at 200 rpm. The overnight cultures were transferred to 200mL liquid LB medium containing 100. mu.g/mL Km at 37 ℃ at 200rpm to an OD600 of about 0.6 at a ratio of 1: 100. To 200mL of the transfer culture, 1M IPTG was added to 500. mu.M at 30 ℃ and 200rpm, and the culture was carried out for 8 hours. The cells were collected and the bacteria were washed 3 times with lysis buffer.

The purification and electrophoresis of Lys C is identical to that of ASD, and the purification is shown in FIG. 2.

The amount of Lys C obtained was 18.17mg/L of the culture broth.

Example 4 Activity assay of recombinant aspartate semialdehyde dehydrogenase

ASD was coupled to Lys C to establish a method for measuring the enzymatic activity of ASD. The measurement principle is as follows:

NADPH in the reaction system has strong light absorption at 340nm of ultraviolet light, and NADP (+) of an oxidation product of the NADPH has no light absorption at 340nm, and the progress of the ASD catalytic reaction can be monitored by utilizing the property.

The reaction was carried out in 96-well plates, and the reaction system was as follows:

setting the temperature of a Perkinelmer EnSpire 2300 of a microplate reader to 37 ℃, putting a 96-hole plate into the microplate reader when the temperature reaches the set value, selecting light absorption by a detection program, measuring the change condition of the light absorption of a reaction system at the wavelength of 340nm, and measuring once per minute and 30 times.

The enzyme activity unit of ASD was defined as the amount of enzyme consuming 1. mu. Mol NADPH per minute under the above reaction conditions as 1U (the enzyme activity unit of Lys C was defined as the amount of enzyme consuming 1. mu. Mol ATP per minute under the same conditions as 1U).

The calculation formula is as follows:

U/ml＝(△A340nm/min test-△A340nm/min blank)×V×df/(×d×v)

wherein V is the total volume of the reaction, and is 0.1 mL; df is the dilution factor of the enzyme ASD, 200; is NADPH millimolar extinction coefficient, 6.22 mL/mol/cm; d is the optical path of a 96-well plate, 0.5 cm; v is the ASD volume, 2. mu.L.

According to the experimental result, the enzyme activity of the ASD is calculated to be 211.69U/mL, and the concentration of the ASD is 1 mug/mL, so that the enzyme activity of the ASD is 211690U/mg; the enzyme activity of the LysC is 431.4U/mL, so the enzyme activity of the LysC is 431400U/mg

Example 5 model for screening Compounds having inhibitory Activity of aspartate semialdehyde dehydrogenase

By optimizing an enzyme activity determination system and setting negative and positive controls, a screening model of the high-throughput inhibitory activity compound of the target ASD is established. The total reaction volume in a 96-well microplate is 100. mu.L, and the components and contents in the system are shown in the following table:

determination of System parameters

Five parameters of signal-to-background ratio (S/B), signal-to-noise ratio (S/N), coefficient of variation (CV%) and Z' factor are selected to evaluate the established model, and the calculation formulas of the parameters are as follows:

S/B＝M_signal/M_background

S/N＝(M_signal-M_background)/(SD² _signal+SD² _background)^1/2

CV％＝SD/M×100

Z’＝1-3×(SD_signal+SD_background)/|M_signal-M_background|

wherein M is_signalThe average value of the light absorption values of the negative control group is the light absorption value of the system in which no reaction occurs;

M_backgroundthe average value of the light absorption values of the positive control group is the absorption value of the system after complete reaction;

SD is the standard deviation.

As can be seen from the above table, the ASD screening system meets the general requirements of a high throughput screening model and is suitable for large-scale screening of compounds having ASD inhibitory activity.

EXAMPLE 6 screening of Compounds with anti-tubercular Activity

Primary screening: a total of 143 compounds having ASD inhibitory activity with an inhibition rate of 30% were obtained by screening 15 ten thousand compound samples of the unit compound library using the screening model of example 5 at a final concentration of 20. mu.g/mL, and the primary screening positivity was 0.953%.

Wherein, the calculation method of the enzyme activity inhibition rate is as follows:

Re-screening: the anti-tuberculosis activity of the obtained compounds is measured, 6 compounds with anti-tuberculosis activity are obtained, and the model is proved to be applicable to the primary screening of novel anti-tuberculosis drugs.

The secondary screening method comprises the following steps:

bacteria: in the presence of 10% ADC (BBL)^TMMiddlebrook ADC enrich) and 0.05% tween-80(BD BBL)^TM) (all available from BD Co., Ltd. (Becton, Dickinson)&Co.)) is used^TMMiddlebrook 7H9 medium (Cat. No.271310) was inoculated with Mycobacterium tuberculosis Standard strain H37Rv (ATCC 27294), cultured with shaking at 37 ℃ to the logarithmic growth phase, 1% inoculated in fresh 7H9 medium (containing ADC and tween-80), and a compound sample (80. mu.g/mL-0.016. mu.g/mL, isoniazid as a positive control) was diluted from the second row using the inoculum with a 2-fold dilution method in a 96-well plate (first row is inoculum, twelfth row is blank medium). The plates were incubated at 37 ℃ for 10 days in a static manner, and the OD600nm light absorption value of the culture broth was determined, taking 99% inhibition of strain growth as its MIC value

Reference documents:

1.Marks,S.M.,et al.,Treatment practices,outcomes,and costs of multidrug-resistant and extensively drug-resistant tuberculosis,United States,2005-2007.Emerg Infect Dis,2014.20(5):p.812-21.

2.Meng,J.,et al.,Identification and Validation of Aspartic Acid Semialdehyde Dehydrogenase as a New Anti-Mycobacterium Tuberculosis Target.Int J Mol Sci,2015.16(10):p.23572-86.

3.Gao,G.,Fragment library screening to discover selective inhibitors of a key microbial enzyme.2010.

4.Cox,R.,J.Gibson,and M.Mayo Martín,Aspartyl phosphonates and phosphoramidates:the first synthetic inhibitors of bacterial aspartate-semialdehyde dehydrogenase.Chembiochem:a European journal of chemical biology,2002.3(9):p.874-886.

5.Shafiani,S.,et al.,Cloning and characterization of aspartate-beta-semialdehyde dehydrogenase from Mycobacterium tuberculosis H37Rv.Journal of applied microbiology,2005.98(4):p.832-838.

6.Kumar,R.,P.Garg,and P.V.Bharatam,Shape-based virtual screening,docking,and molecular dynamics simulations to identify Mtb-ASADH inhibitors.J Biomol Struct Dyn,2015.33(5):p.1082-93.

7.Kumar,R.,P.Garg,and P.V.Bharatam,Pharmacoinformatics analysis to identify inhibitors of Mtb-ASADH.J Biomol Struct Dyn,2015:p.1-14.

while specific embodiments of the invention have been described in detail, it will be appreciated by those skilled in the art that various modifications and alternatives to those details could be developed in light of the overall teachings of the disclosure, and that such modifications are intended to be included within the scope of the disclosure. The full scope of the invention is given by the appended claims and any equivalents thereof.

Claims

1. A method for the heterologous expression of Aspartate Semialdehyde Dehydrogenase (ASD), comprising the steps of:

(1) transferring a strain containing pET28a (+): asd expression plasmid into a culture medium containing Km and an agent for increasing cell osmotic pressure, and culturing to obtain a transfer culture, wherein the agent for increasing cell osmotic pressure is selected from the group consisting of cyclized alpha-1, 4-glucan, cyclodextrine and sorbitol, and the concentration of the agent is 500-1000 mM;

(2) adding IPTG (isopropyl thiogalactoside) into the transfer culture, and culturing at 20-23 ℃ to obtain a thallus cell expressing ASD, wherein the final concentration of IPTG is 5-20 mu M;

2. The method of claim 1, wherein the final concentration of IPTG is 10-15 μ Μ.

3. The method of claim 1, characterized by one or more of the following:

a. the strain in the step (1) is Escherichia coli BL21ATAR^TM(DE3) strain;

b. the Km concentration in the step (1) is 100 mu g/mL;

c. the inoculation amount of the ASD expression strain in the step (1) is 2-10%;

d. the culture conditions of the transfer culture obtained in the step (1) are as follows: culturing at 37 + -2 deg.C and 150-;

f. the culture medium in the step (1) is an LB culture medium;

g. in the step (1), before the transfer, the method further comprises the step of carrying out amplification culture on the strain; h. the culture conditions of the ASD-expressing bacterial cells obtained in the step (2) are as follows: 150-;

i. in the step (3), after the cracking, a purification step is further included.

4. The method of claim 3, wherein the expanding culture is culturing the strain on LB medium containing 100 μ g/mL Km at 37 ℃, 200rpm for 8-16h or to log phase at the bacteria.

5. The method of claim 3, wherein the purification is performed by column chromatography.

6. The method of any one of claims 3-5, further comprising a step of desalting after purification.