Identification of an endogenous polypeptide modulating ligand binding sites of insect neuronal acetylcholine...

In this report evidence is presented for a membrane-associated polypeptide that regulates ligand binding properties of a neuronal acetylcholine receptor. Removal of membrane-associated compounds reversibly increased the number of BGTX binding sites and decreased the number of binding sites for ACh in neuronal membranes, suggesting the existence of endogenous membrane-associated factors that might allosterically modulate the ligand binding sites of receptor protein. The regulatory factor was purified and identified as 20 kDa polypeptide. The purified polypeptide was found to be phosphorylated by cAMP-dependent protein kinase, which caused inactivation of the modulatory polypeptide and thus might control their function.