A human truncated α7 subunit coassembles with the full-length α7 to form functional nicotinic receptors

Abstract

The α7 nicotinic receptor subunit gene, CHRNA7, codes for a subunit that forms the homomeric α7 receptor, which is involved in learning and memory. In humans, exons 5-10 of CHRNA7 were duplicated and fused to the FAM7A gene, given rise to the CHRFA M7A gene. The product of the resulting chimeric gene, dupα7, is a truncated subunit that lacks part of the ACh binding site. We here combined cell expression, confocal microscopy, western blot, and electrophysiological recordings in HEK cells to understand the func tional role of the dupα7 subunit. We found that cells transfected with dupα7 cDNA express the dupα7 protein but show neither surface binding of an α7 specific antagonist nor agonist-elicited currents. To determine if dupα7 assembles with α7 into functional receptors, we used an α7 subunit carrying mutations in determinants of conduct ance (α7LC) as a reporter of receptor stoichiometry. Co-expression of α7LC with dupα7 or the reverse combination, α7 with dupα7LC, allowed detection of single-channel openings elicited by ACh, indi cating that α7 and dupα7 subunits co-assemble into functional het eromeric receptors. The analysis revealed that a minimum of two α7 subunits is required for forming functional receptors and that activa tion of the heteromeric receptors occurs through the α7/α7 interface. Our results contribute to the understanding of the functional signifi cance of the partial duplication of the α7 gene.