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Papers In Press, published online ahead of print October 2, 2002
Department of Biotechnology, Kyoto Sangyo University, Kyoto, Kyoto 603-8555
Corresponding Author: kurosaka{at}cc.kyoto-su.ac.jp
Mucin type O-glycosylation begins with the transfer of GalNAc to serine and threonine residues on proteins by a family of UDP-GalNAc: polypeptide N-acetylgalactosaminlytransferases. These enzymes all contain a lectin-like (QXW)3 repeat sequence at the C-terminus that consists of three tandem repeats (
J. Biol. Chem, 10.1074/jbc.M207369200
Submitted on July 22, 2002
Revised on October 2, 2002
Accepted on October 2, 2002
The lectin domain of UDP-GalNAc: Polypeptide N-acetylgalactosaminyltransferase 1 (GalNAc-T1) is involved in O-glycosylation of a polypeptide with multiple acceptor sites
, 
, and 
). The putative lectin domain of one of the most ubiquitous isozymes, GalNAc-T1, is reportedly not functional. In this report, we have reevaluated the role of the GalNAc-T1 lectin domain. Deletion of the lectin domain resulted in a complete loss of enzymatic activity. We also found that GalNAc-T1 has two activities distinguished by their sensitivities to inhibition with free GalNAc; one activity is sensitive, the other is resistant. In our experiments, the former activity is represented by the O-glycosylation of apomucin, an acceptor that contains multiple glycosylation sites, and the latter by synthetic peptides that contain a single glycosylation site. Site-directed mutagenesis of the lectin domain selectively reduced the former activity, and identified Asp444 in the repeat as the most important site for GalNAc recognition. A further reduction of the GalNAc inhibitable activity was observed when both Asp444 and the corresponding aspartate residues in the and the repeats were mutated. This suggests a cooperative involvement of each repeat unit in the glycosylation of polypeptides with multiple acceptor sites.
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