Differential Vicia villosa Agglutinin Reactivity Identifies Three Distinct Dystroglycan Complexes in Skeletal Muscle

We present evidence for the expression of three α-dystroglycan glycoforms in skeletal muscle cells, including two minor glycoforms marked by either patent or latent reactivity with the N-acetylgalactosamine-specific lectin Vicia villosa agglutinin. Both minor glycoforms co-isolated with β-dystroglycan, but not with other dystrophin/utrophin-glycoprotein complex components, suggesting that they may perform distinct or modified cellular functions. We also confirmed that both patent and latent V. villosa agglutinin-reactive α-dystroglycan glycoforms are expressed in C2C12 myotubes. However, we found that the combined effect of saturating concentrations of V. villosa agglutinin and laminin-1 were strictly additive with respect to acetylcholine receptor cluster formation in C2C12 myotubes, which suggests that laminin-1 and V. villosa agglutinin do not compete for the same binding site on the cell surface. Finally, although β -N-acetylhex-osaminidase digestion dramatically inhibited agrin-, V. villosa agglutinin-, and laminin-1-induced acetylcholine receptor clustering in C2C12 myotubes, treatment with this enzyme had no effect on the amount of α-dystroglycan that was bound to V. villosa agglutinin-agarose. We conclude that α-dystroglycan is not the V. villosa agglutinin receptor implicated in acetylcholine receptor cluster formation. However, our data provide new support for the hypothesis that different glycoforms of α-dystroglycan may perform distinct functions even within the same cell.