Tuberculosis mostly caused by Mycobacterium tuberculosis or Mycobacterium bovis is one of the most dangerous infectious diseases; therefore, it requires searching and discovering new medicines against mycobacteria. Polyamine synthesis and its associated methionine (Met) regeneration pathway have been found to be good drug targets in a variety of microorganisms. The conversion of ketomethiobutyrate (KMTB) to methionine is the final step in this pathway catalyzed by branched-chain amino acid aminotransferases (BCATs).
In this study, the gene encoding for M. bovis BCAT (MbBCAT) was cloned, over-expressed, purified and characterized. Results showed that MbBCAT have optimal temperature at 40-45℃ and optimal pH at near pH 8.5. The kinetic parameters Km, kcat of MbBCAT were 0.12 M, 30 s-1 and 10.34M and 50 s-1 for ketoisocaproate and Glutamte, respectively. In the anlaysis of substrate specificity analysis, KIC and KMV were found to be the best amino-acceptor substrate when glutamte was used as amino-donor. For screening inhibitors against MbBCAT, molecular docking software (Autodock version 1.4.2) was used to evaluate the free energy status after the target enzyme MbBCAT was docked with ligands from chemical banks. Approximately 100,000 compounds were screened in silico, and 10 compounds with less free energy (less than -9) were selected as a possible drug candidate. Among these candidates, Congo Red and Sudan Black were found to possess inhibitory effect on MbBCAT with Ki about 6.5 M and 15.3 M, respectively. The antimycobacterial effects against M. bovis need to cooperate with other labs to further examination for evaluating its promissing for tuberculosis treatment.
