Download MendeleyThe beginnings of mucin biosynthesis: The crystal structure of UDP-GalNAc:polypeptide {alpha}-N-acetylgalactosaminyltransferase-T1
Fritz, T.A., Hurley, J.H., Trinh, L.B., Shiloach, J., Tabak, L.A.(2004) Proc Natl Acad Sci U S A 101: 15307-15312
- PubMed: 15486088
- DOI: https://doi.org/10.1073/pnas.0405657101
- Primary Citation of Related Structures:
1XHB - PubMed Abstract:
UDP-GalNAc:polypeptide alpha-N-acetylgalactosaminyltransferases (ppGaNTases) initiate the formation of mucin-type, O-linked glycans by catalyzing the transfer of alpha-N-acetylgalactosamine from UDP-GalNAc to Ser or Thr residues of core proteins to form the Tn antigen (GalNAc-alpha-1-O-Ser/Thr). ppGaNTases are unique among glycosyltransferases in containing a C-terminal lectin domain. We present the x-ray crystal structure of a ppGaNTase, murine ppGaNTase-T1, and show that it folds to form distinct catalytic and lectin domains. The association of the two domains forms a large cleft in the surface of the enzyme that contains a Mn2+ ion complexed by invariant D209 and H211 of the "DXH" motif and by invariant H344. Each of the three potential lectin domain carbohydrate-binding sites (alpha, beta, and gamma) is located on the active-site face of the enzyme, suggesting a mechanism by which the transferase may accommodate multiple conformations of glycosylated acceptor substrates. A model of a mucin 1 glycopeptide substrate bound to the enzyme shows that the spatial separation between the lectin alpha site and a modeled active site UDP-GalNAc is consistent with the in vitro pattern of glycosylation observed for this peptide catalyzed by ppGaNTase-T1. The structure also provides a template for the larger ppGaNTase family, and homology models of several ppGaNTase isoforms predict dramatically different surface chemistries consistent with isoform-selective acceptor substrate recognition.
Organizational Affiliation:
Section on Biological Chemistry, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, MD 20892, USA.
