ASSOCIATION OF ACETYLCHOLINE-RECEPTORS WITH PERIPHERAL MEMBRANE-PROTEINS - EVIDENCE FROM ANTIBODY-INDUCED COAGGREGATION

Acetylcholine receptors (AChR) are associated with several peripheral membrane proteins that are concentrated on the cytoplasmic face of the plasma membrane at the neuromuscular junction, and at aggregates of A ChR that form in vitro. We tested the linkage among these proteins by inducing microaggregation of AChR, then determining if a given periphe ral membrane protein accumulated with the receptors in microaggregates . In most experiments, we used isolated membrane fragments that are ri ch in AChR and accessible to antibodies against intracellular antigens . We showed that the 43 kD receptor-associated protein always aggregat ed with AChR, whether microaggregation was driven by antibodies to the 43 kD protein, or to the receptor itself. Antibodies to the 58 kD rec eptor-associated protein also always aggregated the 58 kD protein with the receptor. Our results are consistent with a model for AChR-rich m embrane in which the 43 kD and 58 kD proteins are both closely associa ted with the AChR. When we induced microaggregation in intact muscle c ells with anti-AChR antibodies, our results were less definitive. The 43 kD receptor-associated protein microaggregated with AChR, but the 5 8 kD protein was not especially enriched at AChR microaggregates. We d iscuss the advantages of using isolated AChR-rich membrane fragments t o study the association of AChR with peripheral membrane proteins.