Modifying the determinants of α-ketoacid substrate selectivity in mycobacterium tuberculosis α-isopropylmalate synthase

α-Isopropylmalate synthase (IPMS) catalyses the reaction between α-ketoisovalerate and acetyl coenzyme A (AcCoA) in the first step of leucine biosynthesis. IPMS is closely related to homocitrate synthase, which catalyses the reaction between AcCoA and the unbranched α-ketoacid α-ketoglutarate. Analysis of these enzymes suggests that several differently conserved key residues are responsible for the different substrate selectivity. These residues were systematically substituted in the Mycobacterium tuberculosis IPMS, resulting in changes in substrate specificity. A variant of IPMS was constructed with a preference for the unbranched α-ketoacids α-ketobutyrate and pyruvate over the natural branched substrate α-ketoisovalerate.