The beginnings of mucin biosynthesis:: The crystal structure of UDP-GalNAc:polypeptide α-N-acetylgalactosaminyltransferase-T1

被引:120
作者
Fritz, TA
Hurley, JH
Trinh, LB
Shiloach, J
Tabak, LA [1 ]
机构
[1] NIDDKD, Sect Biol Chem, NIH, Dept Hlth & Human Serv, Bethesda, MD 20892 USA
[2] NIDDKD, Mol Biol Lab, NIH, Dept Hlth & Human Serv, Bethesda, MD 20892 USA
[3] NIDDKD, Biotechnol Unit, NIH, Dept Hlth & Human Serv, Bethesda, MD 20892 USA
关键词
glycosyltransferase; mucin;
D O I
10.1073/pnas.0405657101
中图分类号
O [数理科学和化学]; P [天文学、地球科学]; Q [生物科学]; N [自然科学总论];
学科分类号
07 ; 0710 ; 09 ;
摘要
UDP-GaINAc:polypeptide alpha-N-acetylgalactosaminyltransferases (ppGaNTases) initiate the formation of mucin-type, O-linked glycans by catalyzing the transfer of alpha-N-acetylgalactosamine from UDP-GaINAc to Ser or Thr residues of core proteins to form the Tin 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 glycopepticle substrate bound to the enzyme shows that the spatial separation between the lectin alpha site and a modeled active site UDP-GaINAc 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.
引用
收藏
页码:15307 / 15312
页数:6
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