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Publication Abstract from PubMed

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-beta1,3-GlcNAc-beta1,4-(phosphate-6)-Man structure of alpha-dystroglycan (alpha-DG), a subunit of the complex that is anchored to the cell membrane, interacts directly with laminin in the basement membrane. Reduced glycosylation of alpha-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 beta1,2-N-acetylglucosaminyltransferase 1 (POMGnT1), a glycosyltransferase that participates in the formation of GlcNAc-beta1,2-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-beta1,3-GlcNAc-beta1,4-(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 beta-linked GlcNAc of O-mannosyl glycan, an enzymatic product of POMGnT1. This interaction may recruit POMGnT1 to a specific site of alpha-DG to promote GlcNAc-beta1,2-Man clustering and also may recruit other enzymes that interact with POMGnT1, e.g., fukutin, which is required for further modification of the GalNAc-beta1,3-GlcNAc-beta1,4-(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.

Carbohydrate-binding domain of the POMGnT1 stem region modulates O-mannosylation sites of alpha-dystroglycan.,Kuwabara N, Manya H, Yamada T, Tateno H, Kanagawa M, Kobayashi K, Akasaka-Manya K, Hirose Y, Mizuno M, Ikeguchi M, Toda T, Hirabayashi J, Senda T, Endo T, Kato R Proc Natl Acad Sci U S A. 2016 Aug 16;113(33):9280-5. doi:, 10.1073/pnas.1525545113. Epub 2016 Aug 4. PMID:27493216^[2]

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.