Molecular determinants of the selectivity and potency of α-conotoxin Vc1.1 for human nicotinic acetylcholine receptors.

Abstract

The α-conotoxins (α-Ctxs) are short, disulfide-rich peptides derived from the venom of the Conus marine snails, primarily acting as antagonists of nicotinic acetylcholine receptors (nAChRs). Specifically, α-Ctx Vc1.1, a 16-amino acid peptide from C. victoriae, competitively antagonizes non-muscle nAChRs, inhibits nicotine-induced currents in bovine chromaffin cells, and alleviates neuropathic pain in rat models. Although Vc1.1 selectively inhibits rat α9α10 nAChRs, its potency and selectivity across human nAChR subtypes remain unresolved. In this study, we assessed the activity of Vc1.1 on human (h) nAChRs heterologously expressed in Xenopus laevis oocytes using the two-electrode voltage clamp technique and simulated interactions using computational modelling. Vc1.1 selectively antagonized homomeric α9 and heteromeric α3β2 nAChRs, with half-maximal inhibitory concentrations (IC₅₀) of 160 nM and 232 nM, respectively. At hα9[N179A]α10, Vc1.1 exhibited a 20-fold decrease in potency compared to hα9α10, due to the loss of hydrogen bonding with Vc1.1-D11. Conversely, Vc1.1 was four-fold more potent at hα3β2[E86A] compared to hα3β2, possibly influenced by the proximal residue β2-K104, as suggested by molecular dynamics (MD) simulations. Additionally, Vc1.1's potency doubled at hα9[N213K]α10, whereas it remained unchanged at hα9[N213R]α10 nAChRs. MD simulations indicate that altered interactions between the mutant hα9 N179A, N213K, or N213R side chains and Vc1.1-D5 may partly explain these changes in potency. The inhibitory action of Vc1.1 at α9-containing nAChRs is particularly relevant given their role in neuroinflammation, presenting a potential therapeutic pathway for alleviating neuropathic and inflammatory pain. This study provides valuable insights for the rational design of Vc1.1-derived α-Ctxs with enhanced nAChR subtype selectivity.