title: Stoichiometry of the alpha9alpha10 nicotinic cholinergic receptor.
abstract: The alpha9 and alpha10 nicotinic cholinergic subunits assemble to form the receptor that mediates synaptic transmission between efferent olivocochlear fibers and hair cells of the cochlea. They are the latest vertebrate nicotinic cholinergic receptor (nAChR) subunits that have been cloned, and their identification has established a distant early divergent branch within the nAChR gene family. The alpha10 subunit serves as a "structural" component leading to heteromeric alpha9alpha10 nAChRs with distinct properties. We now have probed the stoichiometry of recombinant alpha9alpha10 nAChRs expressed in Xenopus oocytes. We have made use of the analysis of the population of receptors assembled from a wild-type subunit and its partner alpha9 or alpha10 subunit bearing a reporter mutation of a valine to threonine at position 13' of the second transmembrane domain (TM2). Because the mutation increased the sensitivity of the receptor for acetylcholine (ACh) but mutations at different subunits were not equivalent, the number of alpha9 and alpha10 subunits could be inferred from the number of components in compound concentration-response curves to ACh. The results were confirmed via the analysis of the effects of a mutation to threonine at position 17' of TM2. Because at this position the mutations at different subunits were equivalent, the stoichiometry was inferred directly from the shifts in the ACh EC50 values. We conclude that the recombinant alpha9alpha10 receptor is a pentamer with a (alpha9)2(alpha10)3 stoichiometry.
authors.affiliation: Institute of Investigations in Genetic Engineering and Molecular Biology, National Council of Scientific and Technical Investigations, University of Buenos Aires, Buenos Aires 1428, Argentina.
authors.forename: Paola V
authors.initials: PV
authors.lastname: Plazas
authors.forename: Eleonora
authors.initials: E
authors.lastname: Katz
authors.forename: María E
authors.initials: ME
authors.lastname: Gomez-Casati
authors.forename: Cecilia
authors.initials: C
authors.lastname: Bouzat
authors.forename: A Belén
authors.initials: AB
authors.lastname: Elgoyhen
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000595:Amino Acid Sequence; D000818:Animals; D017124:Conserved Sequence; D005260:Female; D008433:Mathematics; D009865:Oocytes; D009994:Osmolar Concentration; D021122:Protein Subunits / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D051381:Rats; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013912:Threonine; D014633:Valine; D014982:Xenopus laevis
chemical_list: C470699:Chrna10 protein, rat; C498541:Chrna9 protein, rat; D021122:Protein Subunits; D011978:Receptors, Nicotinic; D011994:Recombinant Proteins; D013912:Threonine; D014633:Valine; D000109:Acetylcholine