Dynamic Solvation of Protein Cavities Underlies TRPV1 Gating

Abstract

TRPV1 is a member of transient receptor potential (TRP) channels family, which promotes nonselective cationic current across the membrane in response to multiple activating stimuli such as capsaicin, temperature, extracellular pH and voltage. Since TRPV1 is directly involved in nociception, it is among the primary targets for pain-relief drugs. Despite its importance, the gating mechanism of TRPV1 remains unexplored. Here, we applied a combined computational (molecular dynamics and metadynamics simulations) and experimental approach to shed light on the open-to-closed transition of this channel. In particular, we found that the gating of TRPV1 is controlled by a strictly conserved asparagine (N676) in the middle of the S6 helix: this residue is able to rotate from a conformation facing the S4-S5 linker to one facing the central pore. This rotation is correlated with the dehydration of small protein cavities between the linker and the S6 helices and hydration of the central pore. Free energy calculations confirm that the two conformational states are stable and are separated by a relatively low free energy barrier. Based on our findings, we propose a model of TRPV1 gating in which dehydration of the protein pockets determines a rotation of N676; the latter triggers water flow inside of the channel and, ultimately, the opening of the gate. Our model is in line with the known experimental data and has been tested with mutagenesis experiments.