Concanavalin-A binding to acetylcholine receptors: identification of two forms of receptor in denervated rat muscle

Abstract

The interaction of the nicotinic acetylcholine receptor from denervated rat muscle (AChR, solubilized in Triton X-100) and Concanavalin-A (Con-A) was studied by soluble Con-A competing with the binding of AChR to agarose immobilized Con-A, by immuno-precipitation of Con-A-AChR complexes and by inhibition of alpha-bungarotoxin binding to AChR. Results showed that Con-A bound to 85% of all AChR molecules at multiple cooperative binding sites. Con-A caused a partial inhibition of toxin binding to a maximum of 41% of receptors, but only when AChR was first incubated with Con-A before toxin labeling and not when the order was reversed. The blockade of toxin labeling was reversed when the Con-A-AChR complexes were treated with mannose (0.75 M). Receptor-Con-A complexes in which toxin binding was not inhibited showed saturation binding of toxin with a decreased apparent affinity. A sub-population of AChR prepared by affinity purification on Lens Culinaris lectin-agarose columns was 100% inhibited from toxin binding when preincubated with Con-A. We conclude that receptors from denervated rat muscle which bind Con-A (85% of the total AChR) contain two major subpopulations of AChR in the approximate proportions 6:4 that can be distinguished by interactions with lectins having specificity for mannose.