Single Residues in the Outer Pore of TRPV1 and TRPV3 Have Temperature-Dependent Conformations

Sung Eun Kim,Jörg Grandl,Ardem Patapoutian,Sidney Arthur Simon

doi:10.1371/journal.pone.0059593

Abstract

Thermosensation is mediated by ion channels that are highly temperature-sensitive. Several members of the family of transient receptor potential (TRP) ion channels are activated by cold or hot temperatures and have been shown to function as temperature sensors in vivo. The molecular mechanism of temperature-sensitivity of these ion channels is not understood. A number of domains or even single amino acids that regulate temperature-sensitivity have been identified in several TRP channels. However, it is unclear what precise conformational changes occur upon temperature activation. Here, we used the cysteine accessibility method to probe temperature-dependent conformations of single amino acids in TRP channels. We screened over 50 amino acids in the predicted outer pore domains of the heat-activated ion channels TRPV1 and TRPV3. In both ion channels we found residues that have temperature-dependent accessibilities to the extracellular solvent. The identified residues are located within the second predicted extracellular pore loop. These residues are identical or proximal to residues that were shown to be specifically required for temperature-activation, but not chemical activation. Our data precisely locate conformational changes upon temperature-activation within the outer pore domain. Collectively, this suggests that these specific residues and the second predicted pore loop in general are crucial for the temperature-activation mechanism of these heat-activated thermoTRPs.

Highlights

Thermosensation is mediated by sensory neurons that are uniquely excitable by distinct temperatures
We identified single residues with temperature-dependent accessibilities for extracellular solvent in both heat-activated transient receptor potential (TRP) channels
Using homology models of TRPV1 and TRPV3 that are both based on the crystal structure of Kv1.2 (44% homology for the pore region of TRPV1 and 54% for TRPV3) [8] [9], we predicted residues to be in proximity to amino acids that we previously identified to be required for temperature activation [8] [9]

Summary

Introduction

Thermosensation is mediated by sensory neurons that are uniquely excitable by distinct temperatures. The conversion of thermal stimuli into neuronal activity is at least partly carried out by a subset of transient receptor potential ion channels (called thermoTRPs) [1] [2] Expression of these receptors is sufficient to make a naıve cell responsive to heat or cold and genetic ablation of distinct thermoTRPs in mice has been shown to cause specific loss of neuronal excitability by temperatures, altered behavioral temperature-sensitivity and thermal nociception [3] [4] [5]. In a complementary approach Yang and colleagues used fluorescence resonance energy transfer (FRET) and detected conformational changes across subunits of the outer pore domain upon temperature-activation, but not chemical- or voltage-activation [15]. We identified single residues with temperature-dependent accessibilities for extracellular solvent in both heat-activated TRP channels

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