Carbohydrate-binding domain of the POMGnT1 stem region modulates O-mannosylation sites of α-dystroglycan.

Abstract

The dystrophin glycoprotein complex, which connects the cell membrane to the basement membrane, is essential for a variety of biological events, including maintenance of muscle integrity. An O-mannose-type GalNAc-β1,3-GlcNAc-β1,4-(phosphate-6)-Man structure of α-dystroglycan (α-DG), a subunit of the complex that is anchored to the cell membrane, interacts directly with laminin in the basement membrane. Reduced glycosylation of α-DG is linked to some types of inherited muscular dystrophy; consistent with this relationship, many disease-related mutations have been detected in genes involved in O-mannosyl glycan synthesis. Defects in protein O-linked mannose β1,2-N-acetylglucosaminyltransferase 1 (POMGnT1), a glycosyltransferase that participates in the formation of GlcNAc-β1,2-Man glycan, are causally related to muscle-eye-brain disease (MEB), a congenital muscular dystrophy, although the role of POMGnT1 in postphosphoryl modification of GalNAc-β1,3-GlcNAc-β1,4-(phosphate-6)-Man glycan remains elusive. Our crystal structures of POMGnT1 agreed with our previous results showing that the catalytic domain recognizes substrate O-mannosylated proteins via hydrophobic interactions with little sequence specificity. Unexpectedly, we found that the stem domain recognizes the β-linked GlcNAc of O-mannosyl glycan, an enzymatic product of POMGnT1. This interaction may recruit POMGnT1 to a specific site of α-DG to promote GlcNAc-β1,2-Man clustering and also may recruit other enzymes that interact with POMGnT1, e.g., fukutin, which is required for further modification of the GalNAc-β1,3-GlcNAc-β1,4-(phosphate-6)-Man glycan. On the basis of our findings, we propose a mechanism for the deficiency in postphosphoryl modification of the glycan observed in POMGnT1-KO mice and MEB patients.

• Authors: Naoyuki Kuwabara, Hiroshi Manya, Takeyuki Yamada, Hiroaki Tateno, Motoi Kanagawa, Kazuhiro Kobayashi, Keiko Akasaka-Manya, Yuriko Hirose, Mamoru Mizuno, Mitsunori Ikeguchi, Tatsushi Toda, Jun Hirabayashi, Toshiya Senda, Tamao Endo, Ryuichi Kato
• Journal: Proceedings of the National Academy of Sciences of the United States of America (Proc Natl Acad Sci U S A) Vol. 113 Issue 33 Pg. 9280-5 (08 16 2016) ISSN: 1091-6490 [Electronic] United States
• PMID: 27493216 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• DAG1 protein, human
• Dystroglycans
• N-Acetylglucosaminyltransferases
• protein O-mannose beta-1,2-N-acetylglucosaminyltransferase
• Mannose

Topics

• Binding Sites
• Crystallization
• Dystroglycans (chemistry)
• Glycosylation
• Humans
• Mannose (chemistry)
• N-Acetylglucosaminyltransferases (chemistry)