Mouse large can modify complex N- and mucin O-glycans on α-dystroglycan to induce laminin binding

被引:72
作者
Patnaik, SK [1 ]
Stanley, P [1 ]
机构
[1] Albert Einstein Coll Med, Dept Cell Biol, Bronx, NY 10461 USA
关键词
D O I
10.1074/jbc.M500069200
中图分类号
Q5 [生物化学]; Q7 [分子生物学];
学科分类号
071010 ; 081704 ;
摘要
The human LARGE gene encodes a protein with two putative glycosyltransferase domains and is required for the generation of functional alpha-dystroglycan (alpha-DG). Monoclonal antibodies IIH6 and VIA4-1 recognize the functional glycan epitopes of alpha-DG that are necessary for binding to laminin and other ligands. Overexpression of full-length mouse Large generated functionally glycosylated alpha-DG in Pro(-)5 Chinese hamster ovary (CHO) cells, and the amount was increased by co-expression of protein: O-mannosyl N-acetylglucosaminyltransferase 1. However, functional alpha-DG represented only a small fraction of the alpha-DG synthesized by CHO cells or expressed from an alpha-DG construct. To identify features of the glycan epitopes induced by Large, the production of functionally glycosylated alpha-DG was investigated in several CHO glycosylation mutants. Mutants with defective transfer of sialic acid (Lec2), galactose (Lec8), or fucose (Lec13) to glycoconjugates, and the Lec15 mutant that cannot synthesize O-mannose glycans, all produced functionally glycosylated alpha-DG upon overexpression of Large. Laminin binding and the alpha-DG glycan epitopes were enhanced in Lec2 and Lec8 cells. In Lec15 cells, functional alpha-DG was increased by co-expression of core 2 N- acetylglucosaminyltransferase 1 with Large. Treatment with N- glycanase markedly reduced functionally glycosylated alpha-DG in Lec2 and Lec8 cells. The combined data provide evidence that Large does not transfer to Gal, Fuc, or sialic acid on alpha-DG nor induce the transfer of these sugars to alpha-DG. In addition, the data suggest that human LARGE may restore functional alpha-DG to muscle cells from patients with defective synthesis of O-mannose glycans via the modification of N- glycans and/or mucin O-glycans on alpha-DG.
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页码:20851 / 20859
页数:9
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