title: Function of the lectin domain of polypeptide N-acetylgalactosaminyltransferase 1.
abstract: All UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferases cloned to date contain a lectin domain at the C-terminus, consisting of three tandem repeat sequences (alpha,beta, and gamma). We previously reported that the alpha repeat of one of the most ubiquitous isozymes, GalNAc-T1, is a functional lectin that recognizes O-linked GalNAc residues on the acceptor polypeptides with multiple acceptor sites; the domain appears not to be involved in the glycosylation of acceptors with a single acceptor site. In this report, we studied the function of the beta and gamma repeats in the GalNAc-T1 lectin domain, by site-directed mutagenesis and analysis of the catalytic properties of mutant enzymes. We found that the beta repeat recognizes GalNAc and is involved in glycosylation of acceptors with multiple glycosylation sites. The gamma repeat, on the other hand, showed no significant GalNAc-binding activity. These results indicate that the lectin domain of GalNAc-T1 has at least two functional repeats, allowing the possibility of multivalent interactions with GalNAc residues on the acceptor polypeptide during glycosylation.
authors.affiliation: Department of Biotechnology, Faculty of Engineering, Kyoto Sangyo University, Japan.
authors.forename: Mari
authors.initials: M
authors.lastname: Tenno
authors.forename: Ferénc J
authors.initials: FJ
authors.lastname: Kézdy
authors.forename: Ake P
authors.initials: AP
authors.lastname: Elhammer
authors.forename: Akira
authors.initials: A
authors.lastname: Kurosaka
mesh_terms: D000116:Acetylgalactosamine / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D019556:COS Cells; D005752:Gastric Mucins / Q000378:metabolism; D006031:Glycosylation; D066298:In Vitro Techniques; D037102:Lectins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D016297:Mutagenesis, Site-Directed; D017350:N-Acetylgalactosaminyltransferases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D009842:Oligopeptides / Q000737:chemistry / Q000378:metabolism; D017434:Protein Structure, Tertiary; D051381:Rats; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D020449:Repetitive Sequences, Amino Acid; D013379:Substrate Specificity
chemical_list: D005752:Gastric Mucins; D037102:Lectins; D009842:Oligopeptides; D011993:Recombinant Fusion Proteins; C053366:apomucin; D017350:N-Acetylgalactosaminyltransferases; D000116:Acetylgalactosamine