Structure and Reaction Mechanism of YcjR, an Epimerase That Facilitates the Interconversion of d-Gulosides to d-Glucosides in Escherichia coli. Academic Article uri icon

abstract

  • YcjR from Escherichia coli K-12 MG1655 catalyzes the manganese-dependent reversible epimerization of 3-keto--d-gulosides to the corresponding 3-keto--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 -methyl-3-keto-d-glucoside at C4. However, the E240Q mutant can catalyze hydrogen-deuterium exchange of the proton at C4 of -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.

published proceedings

  • Biochemistry

author list (cited authors)

  • Mabanglo, M. F., Huddleston, J. P., Mukherjee, K., Taylor, Z. W., & Raushel, F. M.

publication date

  • January 1, 2020 11:11 AM