GALNT2

HO-Ser/Thr		GalNAc(alpha1-O)-Ser/Thr

This enzyme catalyzes the GalNAc transfer from UDP-GalNAc to Ser or Thr residue in the protein. The product is GalNAc-alpha-O-Ser/Thr structure, so-called Tn-antigen, which is the base structure of mucin type O-glycan. The acceptor substrate (protein) is typically Mucin. GALNT2 is the second member of this enzyme family. In general, this isozyme exhibits strong activities toward some mucin-box-peptides including Pro-rich sequence, for example IgA-hinge peptide. The substrate specificity was clearly explained with the crystal structure (Fritz et al. 2006).
IgA-hinge peptide O-glycan Tn-antigen mucin proline

Glc	Man	Gal	GlcNAc	GalNAc	Fuc	Xyl	Neu5Ac	Neu5Gc	GlcA	IdoA	GlcN