A human-specific, truncated ?7 nicotinic receptor subunit assembles with full-length ?7 and forms functional receptors with different stoichiometries.

ABSTRACT: The cholinergic ?7 nicotinic receptor gene, CHRNA7, encodes a subunit that forms the homopentameric ?7 receptor, involved in learning and memory. In humans, exons 5-10 in CHRNA7 are duplicated and fused to the FAM7A genetic element, giving rise to the hybrid gene CHRFAM7A Its product, dup?7, is a truncated subunit lacking part of the N-terminal extracellular ligand-binding domain and is associated with neurological disorders, including schizophrenia, and immunomodulation. We combined dup?7 expression on mammalian cells with patch clamp recordings to understand its functional role. Transfected cells expressed dup?7 protein, but they exhibited neither surface binding of the ?7 antagonist ?-bungarotoxin nor responses to acetylcholine (ACh) or to an allosteric agonist that binds to the conserved transmembrane region. To determine whether dup?7 assembles with ?7, we generated receptors comprising ?7 and dup?7 subunits, one of which was tagged with conductance substitutions that report subunit stoichiometry and monitored ACh-elicited channel openings in the presence of a positive allosteric ?7 modulator. We found that ?7 and dup?7 subunits co-assemble into functional heteromeric receptors, which require at least two ?7 subunits for channel opening, and that dup?7's presence in the pentameric arrangement does not affect the duration of the potentiated events compared with that of ?7. Using an ?7 subunit mutant, we found that activation of (?7)2(dup?7)3 receptors occurs through ACh binding at the ?7/?7 interfacial binding site. Our study contributes to the understanding of the modulation of ?7 function by the human specific, duplicated subunit, associated with human disorders.

SUBMITTER: Lasala M 

PROVIDER: S-EPMC6036215 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature