Structural correlates of human muscle nicotinic acetylcholine receptor subunit assembly mediated by δ(+) interface residues

Abstract

Muscle nicotinic acetylcholine receptors are a class of heteropentameric ligand-gated cation channels with constituent subunits adopting a fixed stoichiometric arrangement. The specific amino acid residues that govern subunit ordering are however, only partially understood. By integrating all-atom molecular dynamics simulations, bioinformatics, twoelectrode voltage clamp electrophysiology and 125 I-⍺-bungarotoxin assays of chimeric nAChR subunits, we identify residues across the extracellular, transmembrane and extended M4 helix of the δ subunit that make structural signatures that contribute to intransigent assembly rules. Furthermore, functional differences observed in α2δ2β receptors can be rationalized by changes in dynamical behavior that manifest themselves at the agonist binding site.