Polypeptide N-acetylgalactosaminyltransferase 3 (GALNT3)

Catalyzes the initial reaction in O-linked oligosaccharide biosynthesis, the transfer of an N-acetyl-D- galactosamine residue to a serine or threonine residue on the protein receptor. Has activity toward HIV envelope glycoprotein gp120, EA2, Muc2 and Muc5.

Likely glycosylates fibronectin in vivo. Glycosylates FGF23.