title: Identification of N-terminal extracellular domain determinants in nicotinic acetylcholine receptor (nAChR) α6 subunits that influence effects of wild-type or mutant β3 subunits on function of α6β2*- or α6β4*-nAChR.
abstract: Despite the apparent function of naturally expressed mammalian α6*-nicotinic acetylcholine receptors (α6*-nAChR; where * indicates the known or possible presence of additional subunits), their functional and heterologous expression has been difficult. Here, we report that coexpression with wild-type β3 subunits abolishes the small amount of function typically seen for all-human or all-mouse α6β4*-nAChR expressed in Xenopus oocytes. However, levels of function and agonist potencies are markedly increased, and there is atropine-sensitive blockade of spontaneous channel opening upon coexpression of α6 and β4 subunits with mutant β3 subunits harboring valine-to-serine mutations at 9'- or 13'-positions. There is no function when α6 and β2 subunits are expressed alone or in the presence of wild-type or mutant β3 subunits. Interestingly, hybrid nAChR containing mouse α6 and human (h) β4 subunits have function potentiated rather than suppressed by coexpression with wild-type hβ3 subunits and potentiated further upon coexpression with hβ3(V9'S) subunits. Studies using nAChR chimeric mouse/human α6 subunits indicated that residues involved in effects seen with hybrid nAChR are located in the α6 subunit N-terminal domain. More specifically, nAChR hα6 subunit residues Asn-143 and Met-145 are important for dominant-negative effects of nAChR hβ3 subunits on hα6hβ4-nAChR function. Asn-143 and additional residues in the N-terminal domain of nAChR hα6 subunits are involved in the gain-of-function effects of nAChR hβ3(V9'S) subunits on α6β2*-nAChR function. These studies illuminate the structural bases for effects of β3 subunits on α6*-nAChR function and suggest that unique subunit interfaces involving the complementary rather than the primary face of α6 subunits are involved.
authors.affiliation: Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona 85013.
authors.forename: Bhagirathi
authors.initials: B
authors.lastname: Dash
authors.affiliation: Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona 85013.
authors.forename: Minoti
authors.initials: M
authors.lastname: Bhakta
authors.affiliation: Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona 85013.
authors.forename: Yongchang
authors.initials: Y
authors.lastname: Chang
authors.affiliation: Division of Neurobiology, Barrow Neurological Institute, Phoenix, Arizona 85013. Electronic address: rlukas@chw.edu.
authors.forename: Ronald J
authors.initials: RJ
authors.lastname: Lukas
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000928:Antidepressive Agents / Q000627:therapeutic use; D004305:Dose-Response Relationship, Drug; D006801:Humans; D007473:Ion Channels / Q000737:chemistry; D008024:Ligands; D051379:Mice; D008969:Molecular Sequence Data; D018377:Neurotransmitter Agents / Q000378:metabolism; D017354:Point Mutation; D017434:Protein Structure, Tertiary; D011978:Receptors, Nicotinic / Q000737:chemistry* / Q000235:genetics*; D017386:Sequence Homology, Amino Acid; D016540:Smoking Cessation
chemical_list: D000928:Antidepressive Agents; D007473:Ion Channels; D008024:Ligands; D018377:Neurotransmitter Agents; D011978:Receptors, Nicotinic; C559463:alpha6beta2 nicotinic acetylcholine receptor; C104518:nicotinic receptor alpha6