Neuronal nicotinic acetylcholine receptors from Drosophila: Two different types of alpha subunits coassemble within the same receptor complex

Although neuronal nicotinic acetylcholine receptors from insects have been reconstituted in vitro more than a decade ago, our knowledge about the subu nit composition of native receptors as well as their functional properties still remains limited. Immunohistochemical evidence has suggested that two a subunits, alpha-like subunit (ALS) and Drosophila alpha 2 subunit (D alph a 2), are colocalized in the synaptic neuropil of the Drosophila CNS and th erefore may be subunits of the same receptor complex. To gain further under standing of the composition of these nicotinic receptors, we have examined the possibility that a receptor may imbed more than one or subunit using im munoprecipitations and electrophysiological investigations. Immunoprecipita tion experiments of fly head extracts revealed that ALS-specific antibodies coprecipitate D alpha 2, and vice versa, and thereby suggest that these tw o a subunits must be contained within the same receptor complex, a result t hat is supported by investigations of reconstituted receptors in Xenopus oo cytes, Discrimination between binary (ALS/beta 2 or D alpha 2/beta 2) and t ernary (ALS/D alpha 2/beta 2) receptor complexes was made on the basis of t heir dose-response curve to acetylcholine as well as their sensitivity to a lpha-bungarotoxin or dihydro-beta-erythroidine. These data demonstrate that the presence of the two alpha subunits within a single receptor complex co nfers new receptor properties that cannot be predicted from knowledge of th e binary receptor's properties.