May catalyze the formation of some glycolipid via the addition of N-acetylgalactosamine (GalNAc) in alpha-1,3-linkage to some substrate. Glycolipids probably serve for adherence of some pathogens (By similarity). Binds 1 Mn(2+) ion per subunit. Protein modification; protein glycosylation. The conserved DXD motif is involved in cofactor binding. The manganese ion interacts with the beta-phosphate group of UDP and may also have a role in catalysis (By similarity). Belongs to the glycosyltransferase 6 family.