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

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