Reaction catalyzed by mannosylglucosyl-3-phosphoglycerate synthase (2.4.1.270)

		+			=			+
	GDP-mannose	+		2-O-(alpha-D-glucopyranosyl)-3-phospho-D-glycerate	=		GDP	+		2-O-[2-O-(alpha-D-mannopyranosyl)-alpha-D-glucopyranosyl]-3-phospho-D-glycerate