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Publication Abstract from PubMed

While cryo-EM is revolutionizing structural biology, its impact on enzymology is yet to be fully demonstrated. The ketol-acid reductoisomerase (KARI) catalyzes conversion of (2 S)-acetolactate or (2 S)-aceto-2-hydroxybutyrate to 2,3-dihydroxy-3-alkylbutyrate. We found that KARI from archaea Sulfolobus solfataricus (Sso-KARI) is unusual in being a dodecamer, bispecific to NADH and NADPH, and losing activity above pH 7.8. While crystals were obtainable only at pH 8.5, cryo-EM structures were solved at pH 7.5 and 8.5 for Sso-KARI:2Mg(2+). The results showed that the distances of the two catalytic Mg(2+) ions are lengthened in both structures at pH 8.5. We next solved cryo-EM structures of two Sso-KARI complexes, with NADH+inhibitor and NADPH+inhibitor at pH 7.5, which indicate that the bispecificity can be attributed to a unique asparagine at the cofactor binding loop. Unexpectedly, Sso-KARI also differs from other KARI enzymes in lacking "induced-fit", reflecting structural rigidity. Thus, cryo-EM is powerful for structural and mechanistic enzymology.

Use of Cryo-EM To Uncover Structural Bases of pH Effect and Cofactor Bispecificity of Ketol-Acid Reductoisomerase.,Chen CY, Chang YC, Lin BL, Lin KF, Huang CH, Hsieh DL, Ko TP, Tsai MD J Am Chem Soc. 2019 Apr 2. doi: 10.1021/jacs.9b01354. PMID:30921515^[1]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.