Differential Contribution of Subunit Interfaces to ?9?10 Nicotinic Acetylcholine Receptor Function.

ABSTRACT: Nicotinic acetylcholine receptors can be assembled from either homomeric or heteromeric pentameric subunit combinations. At the interface of the extracellular domains of adjacent subunits lies the acetylcholine binding site, composed of a principal component provided by one subunit and a complementary component of the adjacent subunit. Compared with neuronal nicotinic acetylcholine cholinergic receptors (nAChRs) assembled from ? and ? subunits, the ?9?10 receptor is an atypical member of the family. It is a heteromeric receptor composed only of ? subunits. Whereas mammalian ?9 subunits can form functional homomeric ?9 receptors, ?10 subunits do not generate functional channels when expressed heterologously. Hence, it has been proposed that ?10 might serve as a structural subunit, much like a ? subunit of heteromeric nAChRs, providing only complementary components to the agonist binding site. Here, we have made use of site-directed mutagenesis to examine the contribution of subunit interface domains to ?9?10 receptors by a combination of electrophysiological and radioligand binding studies. Characterization of receptors containing Y190T mutations revealed unexpectedly that both ?9 and ?10 subunits equally contribute to the principal components of the ?9?10 nAChR. In addition, we have shown that the introduction of a W55T mutation impairs receptor binding and function in the rat ?9 subunit but not in the ?10 subunit, indicating that the contribution of ?9 and ?10 subunits to complementary components of the ligand-binding site is nonequivalent. We conclude that this asymmetry, which is supported by molecular docking studies, results from adaptive amino acid changes acquired only during the evolution of mammalian ?10 subunits.

SUBMITTER: Boffi JC 

PROVIDER: S-EPMC5325082 | biostudies-literature | 2017 Mar

REPOSITORIES: biostudies-literature