title: B4GAT1 is the priming enzyme for the LARGE-dependent functional glycosylation of α-dystroglycan.
abstract: Recent studies demonstrated that mutations in B3GNT1, an enzyme proposed to be involved in poly-N-acetyllactosamine synthesis, were causal for congenital muscular dystrophy with hypoglycosylation of α-dystroglycan (secondary dystroglycanopathies). Since defects in the O-mannosylation protein glycosylation pathway are primarily responsible for dystroglycanopathies and with no established O-mannose initiated structures containing a β3 linked GlcNAc known, we biochemically interrogated this human enzyme. Here we report this enzyme is not a β-1,3-N-acetylglucosaminyltransferase with catalytic activity towards β-galactose but rather a β-1,4-glucuronyltransferase, designated B4GAT1, towards both α- and β-anomers of xylose. The dual-activity LARGE enzyme is capable of extending products of B4GAT1 and we provide experimental evidence that B4GAT1 is the priming enzyme for LARGE. Our results further define the functional O-mannosylated glycan structure and indicate that B4GAT1 is involved in the initiation of the LARGE-dependent repeating disaccharide that is necessary for extracellular matrix protein binding to O-mannosylated α-dystroglycan that is lacking in secondary dystroglycanopathies.
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, United States.
authors.forename: Jeremy L
authors.initials: JL
authors.lastname: Praissman
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, United States.
authors.forename: David H
authors.initials: DH
authors.lastname: Live
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, United States.
authors.forename: Shuo
authors.initials: S
authors.lastname: Wang
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, United States.
authors.forename: Annapoorani
authors.initials: A
authors.lastname: Ramiah
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, United States.
authors.forename: Zoeisha S
authors.initials: ZS
authors.lastname: Chinoy
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, United States.
authors.forename: Geert-Jan
authors.initials: GJ
authors.lastname: Boons
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, United States.
authors.forename: Kelley W
authors.initials: KW
authors.lastname: Moremen
authors.affiliation: Complex Carbohydrate Research Center, University of Georgia, Athens, United States.
authors.forename: Lance
authors.initials: L
authors.lastname: Wells
mesh_terms: D000595:Amino Acid Sequence; D055162:Biocatalysis; D004187:Disaccharides / Q000378:metabolism; D049030:Dystroglycans / Q000378:metabolism*; D006031:Glycosylation; D057809:HEK293 Cells; D006801:Humans; D007700:Kinetics; D008954:Models, Biological; D008969:Molecular Sequence Data; D017351:N-Acetylglucosaminyltransferases / Q000737:chemistry / Q000378:metabolism*; D010430:Pentosyltransferases / Q000378:metabolism; D012995:Solubility; D013237:Stereoisomerism; D013379:Substrate Specificity; D014312:Trisaccharides / Q000378:metabolism; D014535:Uridine Diphosphate Glucuronic Acid / Q000378:metabolism; D014994:Xylose / Q000737:chemistry / Q000378:metabolism; D000097608:UDP Xylose-Protein Xylosyltransferase
chemical_list: D004187:Disaccharides; D049030:Dystroglycans; D017351:N-Acetylglucosaminyltransferases; D010430:Pentosyltransferases; D014312:Trisaccharides; D014535:Uridine Diphosphate Glucuronic Acid; D014994:Xylose; D000097608:UDP Xylose-Protein Xylosyltransferase; C117674:LARGE1 protein, human; C542575:B4GAT1 protein, human
keywords: B3GNT1; B4GAT1; O-mannosylation; alpha-dystroglycan; biochemistry; congenital muscular dystrophy; glycosylation; human; human biology; medicine