Structural highlights
Publication Abstract from PubMedYcjR from Escherichia coli K-12 MG1655 catalyzes the manganese-dependent reversible epimerization of 3-keto-alpha-d-gulosides to the corresponding 3-keto-alpha-d-glucosides as a part of a proposed catabolic pathway for the transformation of d-gulosides to d-glucosides. The three-dimensional structure of the manganese-bound enzyme was determined by X-ray crystallography. The divalent manganese ion is coordinated to the enzyme by ligation to Glu-146, Asp-179, His-205, and Glu-240. When either of the two active site glutamate residues is mutated to glutamine, the enzyme loses all catalytic activity for the epimerization of alpha-methyl-3-keto-d-glucoside at C4. However, the E240Q mutant can catalyze hydrogen-deuterium exchange of the proton at C4 of alpha-methyl-3-keto-d-glucoside in solvent D2O. The E146Q mutant does not catalyze this exchange reaction. These results indicate that YcjR catalyzes the isomerization of 3-keto-d-glucosides via proton abstraction at C4 by Glu-146 to form a cis-enediolate intermediate that is subsequently protonated on the opposite face by Glu-240 to generate the corresponding 3-keto-d-guloside. This conclusion is supported by docking of the cis-enediolate intermediate into the active site of YcjR based on the known binding orientation of d-fructose and d-psicose in the active site of d-psicose-3-epimerase. Structure and Reaction Mechanism of YcjR, an Epimerase That Facilitates the Interconversion of d-Gulosides to d-Glucosides in Escherichia coli.,Mabanglo MF, Huddleston JP, Mukherjee K, Taylor ZW, Raushel FM Biochemistry. 2020 Jun 9;59(22):2069-2077. doi: 10.1021/acs.biochem.0c00334. Epub, 2020 May 28. PMID:32437133[1] From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine. References
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