Role for a synapse-specific carbohydrate in agrin-induced clustering of acetylcholine receptors.
Lectins such as VVA-B4, which bind N-acetylgalactosaminyl (GalNAc)-terminated saccharides, selectively stain the neuromuscular junction, thus defining a synapse-specific carbohydrate. In seeking roles for this carbohydrate, we asked whether VVA-B4 affected the distribution of acetylcholine receptors (AChRs) on cultured muscle cells. We found that incubation of myotubes with VVA-B4 induced formation of AChR clusters and potentiated the effect of a nerve-derived clustering factor, agrin. Additional experiments implicated GalNAc-terminated glycoconjugates as modulators of agrin-induced AChR clustering. Enzymatic removal of GalNAc residues or treatment with a multivalent protein-GalNAc conjugate blocked agrin-induced clustering, whereas enzymatic unmasking of additional GalNAc residues induced clustering in the absence of added agrin. Moreover, incubation with agrin led to redistribution of VVA-B4-binding material on myotubes. Together, these results suggest that agrin-induced clustering of AChRs involves a GalNAc-dependent step.
Martin
P T
PT
Department of Anatomy and Neurobiology, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Sanes
J R
JR
D000116:Acetylgalactosamine / Q000494:pharmacology*; D018171:Agrin / Q000494:pharmacology*; D000818:Animals; D002241:Carbohydrates / Q000494:pharmacology*; D002460:Cell Line; D004357:Drug Synergism; D037102:Lectins / Q000378:metabolism / Q000494:pharmacology; D051379:Mice; D008856:Microscopy, Fluorescence; D009132:Muscles / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D009469:Neuromuscular Junction / Q000737:chemistry; D037121:Plant Lectins; D011950:Receptors, Cholinergic / Q000187:drug effects / Q000378:metabolism*; D013569:Synapses / Q000737:chemistry*
D018171:Agrin; D002241:Carbohydrates; D037102:Lectins; D037121:Plant Lectins; D011950:Receptors, Cholinergic; C042242:Vicia lectins; D000116:Acetylgalactosamine