galactosyldiacylglycerol alpha-2,3-sialyltransferase activity
Catalysis of the reaction: 1,2-diacyl-3-beta-D-galactosyl-sn-glycerol + CMP-N-acetyl-beta-neuraminate = 1,2-diacyl-3-[3-(alpha-D-N-acetylneuraminyl)-beta-D-galactosyl]-sn-glycerol + CMP + H+.
GO:0008373
sialyltransferase activity
is_a