Alteration of coenzyme specificity of malate dehydrogenase from Streptomyces coelicolor A3(2) by site-directed mutagenesis.

We describe here for the first time the alteration of coenzyme specificity of malate dehydrogenase (MDH) from Streptomyces coelicolor A3(2) (ScMDH). In the present study, we replaced four amino acid residues in the Rossmann fold (ßB-αC) region of NADH-dependent ScMDH by site-directed mutagenesis with those of NADPH-dependent MDH (Glu42Gly, Ile43Ser, Pro45Arg, and Ala46Ser). The coenzyme specificity of the mutant enzyme (ScMDH-T4) was examined. Coenzyme specificity of ScMDH-T4 was shifted 2231.3-fold toward NADPH using kcat/Km(coenzyme) as the measurement of coenzyme specificity. Accordingly, the effect of the replacements on coenzyme specificity is discussed. Our work provides further insight into the coenzyme specificity of ScMDH.