Mycobacterium tuberculosis appears to lack α-ketoglutarate dehydrogenase and encodes pyruvate dehydrogenase in widely separated genes

Mycobacterium tuberculosis (Mtb) persists for prolonged periods in macrophages, where it must adapt to metabolic limitations and oxidative/nitrosative stress. However, little is known about Mtb's intermediary metabolism or antioxidant defences. We recently identified a peroxynitrite reductase-peroxidase complex in Mtb that included products of the genes sucB and Ipd, which are annotated to encode the dihydrolipoamide succinyltransferase (E2) and lipoamide dehydrogenase (E3) components of a-ketoglutarate dehydrogenase (KDH). However, we could detect no KDH activity in Mtb lysates, nor could we reconstitute KDH by combining the recombinant proteins SucA (annotated as the Ell component of KDH), SucB and Lpd. We therefore renamed the sucB product dihydrolipoamide acyltransferase (DIaT). Mtb lysates contained pyruvate dehydrogenase (PDH) activity, which was lost when the dlaT gene (formerly, sucB) was disrupted. Purification of PDH from Mtb yielded AceE, annotated as an El component of PDH, along with DIaT and Lpd. Moreover, anti-DIaT antibody coimmunoprecipitated AceE. Finally, recombinant AceE, DIaT and Lpd, although encoded by genes that are widely separated on the chromosome, reconstituted PDH in vitro with Km values typical of bacterial PDH complexes. In sum, Mtb appears to lack KDH. Instead, DIaT and Lpd join with AceE to constitute PDH.