Purification and characterization of a nicotinic acetylcholine receptor from rat brain

We previously reported the immunoaffinity purification of an acetylcholine receptor from chicken brain that did not bind alpha-bungarotoxin but did bind nicotine and other cholinergic agonists. Antisera and monoclonal antibodies raised against this receptor crossreacted with a receptor from rat brain that had similar pharmacological properties, and also bound to functional acetylcholine receptors in chicken ciliary ganglion cells and rat PC12 cells. Here we report purification of the receptor from rat brain using monoclonal antibody (mAb) 270 raised against receptor from chicken brain. This receptor, similar in size to monomers of receptor from Torpedo electric organ, contained two subunits--apparent Mr, 51,000 and 79,000. The Mr 51,000 subunit was bound by antisera to alpha subunits of receptor from Torpedo electric organ and by mAb 270, which is specific for the Mr 49,000 subunit analogue of receptor from chicken brain. Both subunits were bound by mAb 286, which also binds both subunits of receptors from chicken brain. The alpha-bungarotoxin binding component was purified from the same extracts. It consisted of four subunits of apparent Mr 44,700, 52,300, 56,600, and 65,200. The basic structure of receptors from muscle had evolved to an (alpha)2 beta gamma delta subunit stoichiometry by the time of primitive elasmobranches and is now little changed in mammals. The apparent (alpha)2(beta)2 or (alpha)3(beta)2 structure of the neuronal acetylcholine receptors that we have purified may derive from an early gene duplication event in the evolution of the extended gene family, which now also includes receptors from ganglia and muscle as well as neuronal alpha-bungarotoxin binding sites.