Enhanced laminin binding by α-dystroglycan after enzymatic deglycosylation

Abstract

Carbohydrate modifications are clearly important to the function of α-dystroglycan but their composition and structure remain poorly understood. In the present study, we describe experiments aimed at identifying the α-dystroglycan oligosaccharides important for its binding to laminin-1 and carbohydrate-dependent mAbs (monoclonal antibodies) IIH6 and VIA41. We digested highly purified skeletal muscle α-dystroglycan with an array of linkage-specific endo- and exoglycosidases, which were verified for action on α-dystroglycan by loss/gain of reactivity for lectins with defined glyco-epitopes. Notably, digestion with a combination of Arthrobacter ureafaciens sialidase, β(1-4)galactosidase and β-N-acetylglucosaminidase substantially degraded SiaAα2-3Galβ1-4GlcNAcβ1-2Man glycans on highly purified α-dystroglycan that nonetheless exhibited enhanced IIH6, VIA41 and laminin-1 binding activity. Additional results indicate that α-dystroglycan is probably modified with other anionic sugars besides sialic acid and suggest that rare α-linked GlcNAc moieties may block its complete deglycosylation with currently available enzymes.