Structural domains comprising this superfamily share the structure of family 29 of glycosyl transferases, enzymes involved in the biosynthesis of disaccharides, oligosaccharides and polysaccharides. They catalyse the transfer of sugar moieties from activated donor molecules to specific acceptor molecules, forming glycosidic bonds. Glycosyltransferase family 29 (GT29) comprises enzymes with a number of known activities all of which use a nucleotide monophosphosugar as the donor (CMP-NeuA) instead of a nucleotide diphosphosugar. Probably the best characterised enzymes in this family are sialyltransferases, which catalyse sialyltransfer reactions during glycosylation, and are type II membrane proteins PMID:19820709 PMID:26192331.