Involved in the biosynthesis of the compatible solute mannosylglucosylglycerate through a nonphosphorylating pathway. Catalyzes the synthesis of glucosylglycerate (GG) from ADP-glucose and D-glycerate. Can also use UDP-glucose, with lower efficiency. (R)-glycerate + ADP-alpha-D-glucose = (2R)-2-O-(alpha-D-glucopyranosyl)-glycerate + ADP + H(+) Inhibited by EDTA and Zn(2+). Optimum pH is 7.0 (at 60 degrees Celsius). Optimum temperature is 70-75 degrees Celsius. Homotetramer in solution. Belongs to the glycosyltransferase 2 family.