Vanilloid agonist-mediated activation of TRPV1 channels requires coordinated movement of the S1-S4 bundle rather than a quiescent state

Abstract

Transient receptor potential vanilloid1 (TRPV1) channel plays an important role in a wide range of physiological and pathological processes, and a comprehensive understanding of TRPV1 gating will create opportunities for therapeutic intervention. Recent incredible advances in cryo-electron microscopy (cryo-EM) have yielded high-resolution structures of all TRPV subtypes (TRPV1-6) and all of them share highly conserved six transmembrane (TM) domains (S1-S6). As revealed by the open structures of TRPV1 in the presence of a bound vanilloid agonist (capsaicin or resiniferatoxin), TM helicesS1 to S4 form a bundle that remains quiescent during channel activation, highlighting differences in the gating mechanism of TRPV1 and voltage-gated ion channels. Here, however, we argue that the structural dynamics rather than quiescence of S1-S4 domains is necessary for capsaicin-mediated activation of TRPV1. Using fluorescent unnatural amino acid (flUAA) incorporation and voltage-clamp fluorometry (VCF) analysis, we directly observed allostery of the S1-S4 bundle upon capsaicin binding. Covalent occupation of VCF-identified sites, single-channel recording, cell apoptosis analysis, and exploration of the role of PSFL828, a novel non-vanilloid agonist we identified, have collectively confirmed the essential role of this coordinated S1-S4 motility in capsaicin-mediated activation of TRPV1. This study concludes that, in contrast to cryo-EM structural studies, vanilloid agonists are also required for S1-S4 movement during TRPV1 activation. Redefining the gating process of vanilloid agonists and the discovery of new non-vanilloid agonists will allow the evaluation of new strategies aimed at the development of TRPV1 modulators.

Keywords: Allostery; Ligand-gated ion channels; TRPV1; Vanilloid agonist; Voltage-clamp fluorometry.