D-Hexose-6-phosphate epimerase Ymr099c from Saccharomyces cerevisiae belongs to the large superfamily of aldose-1-epimerases. Its active site is very similar to the catalytic site of galactose mutarotase, the best studied member of the superfamily. It also contains the conserved glutamate and histidine residues that have been shown in galactose mutarotase to be critical for catalysis, the glutamate serving as the active site base to initiate the reaction by removing the proton from the C-1 hydroxyl group of the sugar substrate, and the histidine as the active site acid to protonate the C-5 ring oxygen. In addition Ymr099c contains 2 conserved arginine residues which are involved in phosphate binding, and exhibits hexose-6-phosphate mutarotase activity on glucose-6-P, galactose-6-P and mannose-6-P.
Jiyao W et al.(2023). "The conserved domain database in 2023.",