title: Core 1 glycans on alpha-dystroglycan mediate laminin-induced acetylcholine receptor clustering but not laminin binding.
abstract: Although unique O-linked oligosaccharides on alpha-dystroglycan are important for binding to a variety of extracellular ligands, the function(s) of more generic carbohydrate structures on alpha-dystroglycan remain unclear. Recent studies suggest a role for glycoconjugates bearing the core 1 disaccharide Galbeta(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 alpha-dystroglycan was the predominant jacalin-binding protein detected in C2C12 myotube lysates. Although jacalin likely inhibited laminin-induced AChR clustering by directly binding to alpha-dystroglycan, jacalin had no effect on laminin binding to the myotube surface or to alpha-dystroglycan. Like jacalin, peanut agglutinin lectin also binds the core 1 disaccharide but not when it is terminally sialylated as expressed on alpha-dystroglycan. We show that C2C12 alpha-dystroglycan bound to peanut agglutinin only after digestion with neuraminidase. Simultaneous treatment of myotubes with neuraminidase and endo-O-glycosidase diminished alpha-dystroglycan binding to peanut agglutinin and inhibited neuraminidase-induced AChR clustering. We conclude that sialylated core 1 oligosaccharides of alpha-dystroglycan are important for laminin-induced AChR clustering and that their function in this process is distinct from the established role of alpha-dystroglycan oligosaccharides in laminin binding.
authors.affiliation: Graduate Program in Molecular and Cellular Pharmacology, University of Wisconsin-Madison Medical School, 53706, USA.
authors.forename: Erin L
authors.initials: EL
authors.lastname: McDearmon
authors.forename: Ariana C
authors.initials: AC
authors.lastname: Combs
authors.forename: James M
authors.initials: JM
authors.lastname: Ervasti
mesh_terms: D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000737:chemistry* / Q000502:physiology*; D049030:Dystroglycans; D004591:Electrophoresis, Polyacrylamide Gel; D006026:Glycoside Hydrolases; D007797:Laminin / Q000378:metabolism* / Q000494:pharmacology*; D008562:Membrane Glycoproteins / Q000737:chemistry* / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000378:metabolism; D019158:N-Acetylneuraminic Acid / Q000378:metabolism; D009439:Neuraminidase / Q000494:pharmacology; D019887:Peanut Agglutinin / Q000737:chemistry / Q000378:metabolism; D037121:Plant Lectins / Q000378:metabolism / Q000494:pharmacology*; D011950:Receptors, Cholinergic / Q000187:drug effects / Q000378:metabolism*; D013329:Structure-Activity Relationship
chemical_list: D003598:Cytoskeletal Proteins; D007797:Laminin; D008562:Membrane Glycoproteins; D019887:Peanut Agglutinin; D037121:Plant Lectins; D011950:Receptors, Cholinergic; C043696:jacalin; C121346:laminin 1; D049030:Dystroglycans; D006026:Glycoside Hydrolases; D009439:Neuraminidase; D019158:N-Acetylneuraminic Acid