Differential Contribution of Subunit Interfaces to a9a10 Nicotinic Acetylcholine Receptor Function

BOFFI JC; MARCOVICH I; GILL-THIND JC; CORRADI J; COLLINS T; LIPOVSEK MM; MOGLIE M; PLAZAS P; CRAIG P; MILLAR N; BOUZAT C; ELGOYHEN AB

MOLECULAR PHARMACOLOGY

AMER SOC PHARMACOLOGY EXPERIMENTAL THERAPEUTICS

Lugar: Baltimore; Año: 2017 vol. 91 p. 250 - 262

0026-895X

Nicotinic acetylcholine receptors can be assembled from eitherhomomeric or heteromeric pentameric subunit combinations. Atthe interface of the extracellular domains of adjacent subunitslies the acetylcholine binding site, composed of a principalcomponent provided by one subunit and a complementarycomponent of the adjacent subunit. Compared with neuronalnicotinic acetylcholine cholinergic receptors (nAChRs) assembledfrom a and b subunits, the a9a10 receptor is an atypicalmember of the family. It is a heteromeric receptor composedonly of a subunits. Whereas mammalian a9 subunits can formfunctional homomeric a9 receptors, a10 subunits do notgenerate functional channels when expressed heterologously.Hence, it has been proposed that a10 might serve as a structuralsubunit, much like a b subunit of heteromeric nAChRs, providingonly complementary components to the agonist binding site.Here, we have made use of site-directed mutagenesis toexamine the contribution of subunit interface domains toa9a10 receptors by a combination of electrophysiological andradioligand binding studies. Characterization of receptors containingY190T mutations revealed unexpectedly that both a9 anda10 subunits equally contribute to the principal components ofthe a9a10 nAChR. In addition, we have shown that the introductionof a W55T mutation impairs receptor binding andfunction in the rat a9 subunit but not in the a10 subunit,indicating that the contribution of a9 and a10 subunits tocomplementary components of the ligand-binding site is nonequivalent.We conclude that this asymmetry, which is supportedby molecular docking studies, results from adaptiveamino acid changes acquired only during the evolution ofmammalian a10 subunits