title: Differential glycosylation of α-dystroglycan and proteins other than α-dystroglycan by like-glycosyltransferase.
abstract: Genetic defects in like-glycosyltransferase (LARGE) cause congenital muscular dystrophy with central nervous system manifestations. The underlying molecular pathomechanism is the hypoglycosylation of α-dystroglycan (α-DG), which is evidenced by diminished immunoreactivity to IIH6C4 and VIA4-1, antibodies that recognize carbohydrate epitopes. Previous studies indicate that LARGE participates in the formation of a phosphoryl glycan branch on O-linked mannose or it modifies complex N- and mucin O-glycans. In this study, we overexpressed LARGE in neural stem cells deficient in protein O-mannosyltransferase 2 (POMT2), an enzyme required for O-mannosyl glycosylation. The results showed that overexpressing LARGE did not lead to hyperglycosylation of α-DG in POMT2 knockout (KO) cells but did generate IIH6C4 and VIA4-1 immunoreactivity and laminin-binding activity. Additionally, overexpressing LARGE in cells deficient in both POMT2 and α-DG generated laminin-binding IIH6C4 immunoreactivity. These results indicate that LARGE expression resulted in the glycosylation of proteins other than α-DG in the absence of O-mannosyl glycosylation. The IIH6C4 immunoreactivity generated in double-KO cells was largely removed by treatment either with peptide N-glycosidase F or with cold aqueous hydrofluoric acid, suggesting that LARGE expression caused phosphoryl glycosylation of N-glycans. However, the glycosylation of α-DG by LARGE is dependent on POMT2, indicating that LARGE expression only modifies O-linked mannosyl glycans of α-DG. Thus, LARGE expression mediates the phosphoryl glycosylation of not only O-mannosyl glycans including those on α-DG but also N-glycans on proteins other than α-DG.
authors.affiliation: Department of Neuroscience and Physiology,  SUNY Upstate Medical University, 750 E. Adams Street, Syracuse, NY 13210,  USA.
authors.forename: Peng
authors.initials: P
authors.lastname: Zhang
authors.forename: Huaiyu
authors.initials: H
authors.lastname: Hu
mesh_terms: D000818:Animals; D049030:Dystroglycans / Q000235:genetics / Q000276:immunology / Q000378:metabolism*; D055786:Gene Knockout Techniques; D006023:Glycoproteins / Q000378:metabolism; D006031:Glycosylation; D016695:Glycosyltransferases / Q000235:genetics / Q000378:metabolism*; D007797:Laminin / Q000378:metabolism; D008364:Mannosyltransferases / Q000172:deficiency* / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D009136:Muscular Dystrophies / Q000235:genetics / Q000276:immunology; D058953:Neural Stem Cells / Q000378:metabolism; D011134:Polysaccharides / Q000378:metabolism*; D011485:Protein Binding
chemical_list: D006023:Glycoproteins; D007797:Laminin; D011134:Polysaccharides; D049030:Dystroglycans; D016695:Glycosyltransferases; D008364:Mannosyltransferases; C082696:protein O-mannosyltransferase