Uncoupling Proton Activation of Vanilloid Receptor TRPV1

Abstract

Multimodal gating is an essential feature of many TRP ion channels, enabling them to respond to complex cellular environments. TRPV1, a pain receptor involved in nociception at the peripheral nerve terminals, can be activated by a range of physical and chemical stimuli (e.g., capsaicin, proton, and heat) and further sensitized by proinflammatory substances. How a single receptor achieves this multiplicity of functionality is poorly understood at the molecular level. Here, we investigated the structural basis of proton activation of TRPV1. Chimeric channels between rTRPV1 and the low pH-insensitive homolog TRPV2 were constructed by systematically exchanging the extracellular domains and were characterized using whole-cell recording in transiently transfected HEK293 cells. Two discrete domains, one involving the pore helix and the other the S3-S4 linker, were found crucial for direct activation of the channel by low pH. Single residue mutations in either domain (T633A/V538L) abrogated the proton-evoked current while preserving the capsaicin and heat responses and their potentiation by mildly acidic pH. Both residues exert a gating effect through hydrophobic interactions. Our results unravel novel information on the structural basis of channel function, and support the existence of discrete domains for multimodal gating of the channel. In view of the resemblance of the pore of TRPV1 to KcsA, our findings also provide evidence on the pore helix as an active component in channel gating in addition to its role in ion permeation.

Intracellular Proton-mediated Activation of TRPV3 Channels Accounts for the Exfoliation Effect of α-Hydroxyl Acids on Keratinocytes

“…Cell acidification can serve as a concomitant of cell death (63) and a means to detect painful conditions, especially in deep tissues where the temperature is expected to remain constant (64). A number of TRP channels have been shown to be quite sensitive to changes in extracellular pH (65,66). Although intracellular acidification-mediated inhibition has been observed in TRPV5 and TRPM2 channels (67,68), our findings represent the first demonstration of intracellular acidification-mediated activation by a member of the TRPV channel family.…”

Forward Genetic Analysis Reveals Multiple Gating Mechanisms of TRPV4

“…There is evidence that the filter region plays an important role in the gating of the closely related TRPV1 channel (26,37), and filter region gating underlies C-type inactivation in other cation channels (38). If such a mechanism is at play here, then it is tempting to speculate that voltage is not directly controlling gating but instead the direction of the driving force (i.e.…”

Distinct Modulations of Human Capsaicin Receptor by Protons and Magnesium through Different Domains

“…This linker, although short, constrains the structure of the TM1-4 domain of TRPV1 to impact its function significantly. Amino acid substitutions within this linker had been shown to obliterate the activation of TRPV1 by extremely acidic pH, even if the residues involved are not directly titratable by protons (27). Although modulatory effects of magnesium on human TRPV1 phenocopy those of protons in both the polarity and the magnitude, immediate sites of actions of these two cations are different.…”

“…Within the extracellular linker between TM3 and TM4, which has also been shown to be critical for direct activation of rTRPV1 by strong acidic pH (27), a histidine residue is present that is unique to the human receptor (Fig. 6A).…”