Crystal Structure and Biochemical Characterization of Ketol-Acid Reductoisomerase from .

l-Valine belongs to the branched-chain amino acids (BCAAs) and is an essential amino acid that is crucial for all living organisms. l-Valine is industrially produced by the nonpathogenic bacterium and is synthesized by the BCAA biosynthetic pathway. Ketol-acid reductoisomerase (KARI) is the second enzyme in the BCAA pathway and catalyzes the conversion of ()-2-acetolactate into ()-2,3-dihydroxy-isovalerate, or the conversion of ()-2-aceto-2-hydroxybutyrate into ()-2,3-dihydroxy-3-methylvalerate. To elucidate the enzymatic properties of KARI from (KARI), we successfully produced KARI protein and determined its crystal structure in complex with NADP and two Mg ions. Based on the complex structure, docking simulations, and site-directed mutagenesis experiments, we revealed that KARI belongs to Class I KARI and identified key residues involved in stabilization of the substrate, metal ions, and cofactor. Furthermore, we confirmed the difference in the binding of metal ions that depended on the conformational change.