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J. Biol. Chem., Vol. 278, Issue 45, 44868-44873, November 7, 2003

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Core 1 Glycans on -Dystroglycan Mediate Laminin-induced Acetylcholine Receptor Clustering but Not Laminin Binding^*

Erin L. McDearmon, Ariana C. Combs, and James M. Ervasti¶

From the Graduate Program in Molecular and Cellular Pharmacology and the Department of Physiology, University of Wisconsin-Madison Medical School, Madison, Wisconsin 53706

Although unique O-linked oligosaccharides on -dystroglycan are important for binding to a variety of extracellular ligands, the function(s) of more generic carbohydrate structures on -dystroglycan remain unclear. Recent studies suggest a role for glycoconjugates bearing the core 1 disaccharide Gal(1–3)GalNAc in acetylcholine receptor (AChR) clustering on the surface of muscle cells. Here, we report experiments demonstrating that the core 1-specific lectin jacalin almost completely abrogated laminin-induced AChR clustering in C2C12 myotubes and that -dystroglycan was the predominant jacalin-binding protein detected in C2C12 myotube lysates. Although jacalin likely inhibited laminin-induced AChR clustering by directly binding to -dystroglycan, jacalin had no effect on laminin binding to the myotube surface or to -dystroglycan. Like jacalin, peanut agglutinin lectin also binds the core 1 disaccharide but not when it is terminally sialylated as expressed on -dystroglycan. We show that C2C12 -dystroglycan bound to peanut agglutinin only after digestion with neuraminidase. Simultaneous treatment of myotubes with neuraminidase and endo-O-glycosidase diminished -dystroglycan binding to peanut agglutinin and inhibited neuraminidase-induced AChR clustering. We conclude that sialylated core 1 oligosaccharides of -dystroglycan are important for laminin-induced AChR clustering and that their function in this process is distinct from the established role of -dystroglycan oligosaccharides in laminin binding.

Received for publication, July 1, 2003 , and in revised form, August 15, 2003.

^* This work was supported by the Muscular Dystrophy Association and National Institutes of Health Grant ARO1985 (to J. M. E.) and an American Heart Association-Northland Affiliate Pre-Doctoral Fellowship (to E. L. M.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.

^¶ To whom correspondence should be addressed: Dept. of Physiology, University of Wisconsin-Madison, 127 Service Memorial Institute, 1300 University Ave., Madison, WI 53706. Tel.: 608-265-3419; Fax: 608-265-5512; E-mail: ervasti{at}physiology.wisc.edu.

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