The lectin domain of UDP-N-acetyl-D-galactosamine: polypeptide N-acetylgalactosaminyltransferase-T4 directs its glycopeptide specificities.
The initiation step of mucin-type O-glycosylation is controlled by a large family of homologous UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases (GalNAc-transferases). Differences in kinetic properties, substrate specificities, and expression patterns of these isoenzymes provide for differential regulation of O-glycan attachment sites and density. Recently, it has emerged that some GalNAc-transferase isoforms in vitro selectively function with partially GalNAc O-glycosylated acceptor peptides rather than with the corresponding unglycosylated peptides. O-Glycan attachment to selected sites, most notably two sites in the MUC1 tandem repeat, is entirely dependent on the glycosylation-dependent function of GalNAc-T4. Here we present data that a putative lectin domain found in the C terminus of GalNAc-T4 functions as a GalNAc lectin and confers its glycopeptide specificity. A single amino acid substitution in the lectin domain of a secreted form of GalNAc-T4 selectively blocked GalNAc-glycopeptide activity, while the general activity to peptides exerted by this enzyme was unaffected. Furthermore, the GalNAc-glycopeptide activity of wild-type secreted GalNAc-T4 was selectively inhibited by free GalNAc, while the activity with peptides was unaffected.
Hassan
H
H
Faculty of Health Sciences, School of Dentistry, Copenhagen DK-2200, Denmark.
Reis
C A
CA
Bennett
E P
EP
Mirgorodskaya
E
E
Roepstorff
P
P
Hollingsworth
M A
MA
Burchell
J
J
Taylor-Papadimitriou
J
J
Clausen
H
H
D000595:Amino Acid Sequence; D000818:Animals; D016466:CHO Cells; D020134:Catalytic Domain; D002460:Cell Line; D006224:Cricetinae; D006020:Glycopeptides / Q000737:chemistry* / Q000378:metabolism*; D006031:Glycosylation; D007527:Isoenzymes / Q000737:chemistry / Q000378:metabolism; D007700:Kinetics; D037102:Lectins / Q000737:chemistry*; D008969:Molecular Sequence Data; D018396:Mucin-1 / Q000737:chemistry / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D017350:N-Acetylgalactosaminyltransferases / Q000737:chemistry* / Q000378:metabolism*; D010446:Peptide Fragments / Q000737:chemistry / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D013379:Substrate Specificity; D014162:Transfection; D000097763:Polypeptide N-acetylgalactosaminyltransferase
D006020:Glycopeptides; D007527:Isoenzymes; D037102:Lectins; D018396:Mucin-1; D017350:N-Acetylgalactosaminyltransferases; D010446:Peptide Fragments; D011994:Recombinant Proteins; D000097763:Polypeptide N-acetylgalactosaminyltransferase