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

Proc Natl Acad Sci U S A. 2016 Aug 16;113(33):9280-5. doi: 10.1073/pnas.1525545113.

Naoyuki Kuwabara ¹, Hiroshi Manya ², Takeyuki Yamada ², Hiroaki Tateno ³, Motoi Kanagawa ⁴, Kazuhiro Kobayashi ⁴, Keiko Akasaka-Manya ², Yuriko Hirose ⁵, Mamoru Mizuno ⁵, Mitsunori Ikeguchi ⁶, Tatsushi Toda ⁴, Jun Hirabayashi ³, Toshiya Senda ⁷, Tamao Endo ⁸, Ryuichi Kato ⁹

Affiliations

1 Photon Factory, Structural Biology Research Center, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan;
2 Tokyo Metropolitan Geriatric Hospital and Institute of Gerontology, Itabashi-ku, Tokyo 173-0015, Japan;
3 Biotechnology Research Institute for Drug Discovery, National Institute of Advanced Industrial Science and Technology, Tsukuba, Ibaraki 305-8568, Japan;
4 Division of Neurology/Molecular Brain Science, Kobe University Graduate School of Medicine, Kobe, Hyogo 650-0017, Japan;
5 Laboratory of Glyco-organic Chemistry, The Noguchi Institute, Itabashi-ku, Tokyo 173-0003, Japan;
6 Graduate School of Medical Life Science, Yokohama City University, Yokohama, Kanagawa 230-0045, Japan;
7 Photon Factory, Structural Biology Research Center, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan; School of High Energy Accelerator Science, SOKENDAI University, Tsukuba, Ibaraki 305-0801, Japan.
8 Tokyo Metropolitan Geriatric Hospital and Institute of Gerontology, Itabashi-ku, Tokyo 173-0015, Japan; ryuichi.kato@kek.jp endo@tmig.or.jp.
9 Photon Factory, Structural Biology Research Center, Institute of Materials Structure Science, High Energy Accelerator Research Organization, Tsukuba, Ibaraki 305-0801, Japan; School of High Energy Accelerator Science, SOKENDAI University, Tsukuba, Ibaraki 305-0801, Japan ryuichi.kato@kek.jp endo@tmig.or.jp.

PMID: 27493216 DOI: 10.1073/pnas.1525545113

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.

Keywords

O-mannosyl glycan; glycosyltransferase; lectin; muscular dystrophy; α-dystroglycanopathy.

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