Probable glycopeptide transferase involved in O-linked oligosaccharide biosynthesis. Glycopeptide transferases catalyze the transfer of an N-acetyl-D-galactosamine residue to an already glycosylated peptide (By similarity). In contrast to other members of the family, it does not act as a peptide transferase that transfers GalNAc onto serine or threonine residue on peptides that have been tested. Some peptide transferase activity is however not excluded, considering that its appropriate peptide substrate may remain unidentified. Protein modification; protein glycosylation. There are two conserved domains in the glycosyltransferase region: the N-terminal domain (domain A, also called GT1 motif), which is probably involved in manganese coordination and substrate binding and the C-terminal domain (domain B, also called Gal/GalNAc-T motif), which is probably involved in catalytic reaction and UDP-Gal binding. The ricin B-type lectin domain binds to GalNAc and contributes to the glycopeptide specificity. Belongs to the glycosyltransferase 2 family. GalNAc-T subfamily.