A novel human UDP-N-acetyl-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase, GalNAc-T7, with specificity for partial GalNAc-glycosylated acceptor substrates

A novel member of the human UDP-N-acetyl-D-galactosamine:polypeptide N-acetylgalactosaminyltransferase gene family, designated GalNAc-T7, was cloned and expressed. GalNAc-T7 exhibited different properties compared to other characterized members of this gene family, in showing apparent exclusive specificity for partially GalNAc-glycosylated acceptor substrates. GalNAc-T7 showed no activity with a large panel of non-glycosylated Peptides, but was selectively activated by partial GalNAc glycosylation of peptide substrates derived from the tandem repeats of human MUC2 and rat submaxillary gland Mucin. The function of GalNAc-T7 is suggested to be as a follow-up Enzyme in the initiation step of O-glycosylation.