Characterization of TrpE and PabB from Mycobacterium tuberculosis

While E. coli uses ubiquinone and menaquinone as electron shuttles in its aerobic and anaerobic respiration processes, respectively, Mycobacterium tuberculosis (Mtb) has menaquinone as its sole quinone. Since latent Mtb must respire to remain viable, inhibitors of menaquinone biosynthesis could potentially be active against both replicating and non‐replicating populations of bacteria. The initial step from chorismate to isochorismate in the pathway is carried out by the isochorismate synthase, MenF, in E. coli. However, there is no annotated menF gene in Mtb genome. We expressed Mtb MbtI, EntC, TrpE and PabB, the four enzymes with the highest similarity to E. coli MenF, in search of the isochorismate synthase that is utilized in Mtb for menaquinone biosynthesis. This report will focus on characterization of TrpE and PabB from Mtb. TrpE displays typical anthranilate synthase activities, including anthranilate production, Mg2+ and NH4+ dependence, and feedback inhibition by tryptophan. Unexpectedly, prephenate formation is also observed. PabB catalyzes a two‐step reaction which is consistent with an aminodeoxychorismate synthase activity. Thus the possibilities of TrpE or PabB being the E. coli MenF counterpart in Mtb can almost be ruled out. The study nevertheless adds new evidence to the catalytic specificity (or promiscuity) of these chorismate‐utilizing enzymes.