The allosteric activation of α7 nAChR by α-conotoxin MrIC is modified by mutations at the vestibular site

Abstract

α-conotoxins are 13-19 amino acid toxin peptides that bind various nicotinic acetylcholine receptor (nAChR) subtypes. α-conotoxin Mr1.7c (MrIC) is a 17 amino acid peptide that targets α7 nAChR. Although MrIC has no activating effect on α7 nAChR when applied by itself, it evokes a large response when co-applied with the type II positive allosteric modulator PNU-120596, which potentiates α7 nAChR response by recovering it from a desensitized state. Lack of standalone activity despite activation upon co-application with a positive allosteric modulator was previously observed for molecules that bind to an extracellular domain allosteric activation (AA) site at the vestibule of the receptor. We hypothesized that MrIC may activate α7 nAChR allosterically through this site. We ran voltage-clamp electrophysiology experiments and in silico peptide docking calculations to gather evidence in support of α7 nAChR activation by MrIC through the AA site. The experiments with the wild-type α7 nAChR supported an allosteric mode of action, which was confirmed by the increased MrIC + PNU-120596 responses of three α7 nAChR AA site mutants that were designed in silico to improve MrIC binding. Overall, our results shed light on allosteric activation of α7 nAChR by MrIC and suggest involvement of the AA site.

Venom-derived pain-causing toxins: insights into sensory neuron function and pain mechanisms

“…For example, the a-conotoxin MrIC activates the a7 nAChR through allosteric mechanisms. 48,88 Similarly, the x-conotoxin MrIA seems to interact with the norepinephrine transporter through allosteric binding to a large hydrophobic pocket of the transporter. 10 These types of studies can inform the rational design of analgesic peptides or small molecules.…”