Identification of N-terminal extracellular domain determinants in nicotinic acetylcholine receptor (nAChR) ?6 subunits that influence effects of wild-type or mutant ?3 subunits on function of ?6?2*- or ?6?4*-nAChR.

ABSTRACT: Despite the apparent function of naturally expressed mammalian ?6*-nicotinic acetylcholine receptors (?6*-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 ?3 subunits abolishes the small amount of function typically seen for all-human or all-mouse ?6?4*-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 ?6 and ?4 subunits with mutant ?3 subunits harboring valine-to-serine mutations at 9'- or 13'-positions. There is no function when ?6 and ?2 subunits are expressed alone or in the presence of wild-type or mutant ?3 subunits. Interestingly, hybrid nAChR containing mouse ?6 and human (h) ?4 subunits have function potentiated rather than suppressed by coexpression with wild-type h?3 subunits and potentiated further upon coexpression with h?3(V9'S) subunits. Studies using nAChR chimeric mouse/human ?6 subunits indicated that residues involved in effects seen with hybrid nAChR are located in the ?6 subunit N-terminal domain. More specifically, nAChR h?6 subunit residues Asn-143 and Met-145 are important for dominant-negative effects of nAChR h?3 subunits on h?6h?4-nAChR function. Asn-143 and additional residues in the N-terminal domain of nAChR h?6 subunits are involved in the gain-of-function effects of nAChR h?3(V9'S) subunits on ?6?2*-nAChR function. These studies illuminate the structural bases for effects of ?3 subunits on ?6*-nAChR function and suggest that unique subunit interfaces involving the complementary rather than the primary face of ?6 subunits are involved.

SUBMITTER: Dash B 

PROVIDER: S-EPMC3207470 | biostudies-literature | 2011 Nov

REPOSITORIES: biostudies-literature