Amino Acids Allosterically Regulate the Thiamine Diphosphate-dependent α-Keto Acid Decarboxylase from Mycobacterium tuberculosis

The gene rv0853c from Mycobacterium tuberculosis strain H37Rv codes for a thiamine diphosphate-dependent α-keto acid decarboxylase ( Mt KDC), an enzyme involved in the amino acid degradation via the Ehrlich pathway. Steady state kinetic experiments were performed to determine the substrate specificity of Mt KDC. The mycobacterial enzyme was found to convert a broad spectrum of branched-chain and aromatic α-keto acids. Stopped-flow kinetics showed that Mt KDC is allosterically activated by α-keto acids. Even more, we demonstrate that also amino acids are potent activators of this thiamine diphosphate-dependent enzyme. Thus, metabolic flow through the Ehrlich pathway can be directly regulated at the decarboxylation step. The influence of amino acids on Mt KDC catalysis was investigated, and implications for other thiamine diphosphate-dependent enzymes are discussed.