Virulence of Mycobacterium tuberculosis Depends on Lipoamide Dehydrogenase, a Member of Three Multienzyme Complexes

SummaryMycobacterium tuberculosis (Mtb) adapts to persist in a nutritionally limited macrophage compartment. Lipoamide dehydrogenase (Lpd), the third enzyme (E3) in Mtb's pyruvate dehydrogenase complex (PDH), also serves as E1 of peroxynitrite reductase/peroxidase (PNR/P), which helps Mtb resist host-reactive nitrogen intermediates. In contrast to Mtb lacking dihydrolipoamide acyltransferase (DlaT), the E2 of PDH and PNR/P, Lpd-deficient Mtb is severely attenuated in wild-type and immunodeficient mice. This suggests that Lpd has a function that DlaT does not share. When DlaT is absent, Mtb upregulates an Lpd-dependent branched-chain keto acid dehydrogenase (BCKADH) encoded by pdhA, pdhB, pdhC, and lpdC. Without Lpd, Mtb cannot metabolize branched-chain amino acids and potentially toxic branched-chain intermediates accumulate. Mtb deficient in both DlaT and PdhC phenocopies Lpd-deficient Mtb. Thus, Mtb critically requires BCKADH along with PDH and PNR/P for pathogenesis. These findings position Lpd as a potential target for anti-infectives against Mtb.

Graphical AbstractFigure optionsDownload full-size imageDownload high-quality image (261 K)Download as PowerPoint slideHighlights► Mtb lacking lipoamide dehydrogenase (Lpd) is highly attenuated in mice ► Lpd-deficient Mtb cannot metabolize branched-chain amino acids ► Lpd functions in Mtb's branched-chain keto acid dehydrogenase complex (BCKADH) ► Disruption of both pyruvate dehydrogenase and BCKADH phenocopies loss of Lpd