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The functional O-mannose glycan on α-dystroglycan contains a phospho-ribitol primed for matriglycan addition
Journal article   Open access   Peer reviewed

The functional O-mannose glycan on α-dystroglycan contains a phospho-ribitol primed for matriglycan addition

Jeremy L Praissman, Tobias Willer, M Osman Sheikh, Ants Toi, David Chitayat, Yung-Yao Lin, Hane Lee, Stephanie H Stalnaker, Shuo Wang, Pradeep Kumar Prabhakar, …
eLife, Vol.5, e14473
04/29/2016
DOI: 10.7554/eLife.14473
PMCID: PMC4924997
PMID: 27130732
url
https://doi.org/10.7554/eLife.14473View
Published (Version of record) Open Access

Abstract

Multiple glycosyltransferases are essential for the proper modification of alpha-dystroglycan, as mutations in the encoding genes cause congenital/limb-girdle muscular dystrophies. Here we elucidate further the structure of an O-mannose-initiated glycan on alpha-dystroglycan that is required to generate its extracellular matrix-binding polysaccharide. This functional glycan contains a novel ribitol structure that links a phosphotrisaccharide to xylose. ISPD is a CDP-ribitol (ribose) pyrophosphorylase that generates the reduced sugar nucleotide for the insertion of ribitol in a phosphodiester linkage to the glycoprotein. TMEM5 is a UDP-xylosyl transferase that elaborates the structure. We demonstrate in a zebrafish model as well as in a human patient that defects in TMEM5 result in muscular dystrophy in combination with abnormal brain development. Thus, we propose a novel structure-a ribitol in a phosphodiester linkage-for the moiety on which TMEM5, B4GAT1, and LARGE act to generate the functional receptor for ECM proteins having LG domains.
Animals Humans Ribitol - analysis Dystroglycans - metabolism Extracellular Matrix - metabolism Protein Binding Dystroglycans - chemistry Zebrafish Membrane Proteins - metabolism Nucleotidyltransferases - metabolism Polysaccharides - analysis Mannose - analysis

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