Modular thermal sensors in temperature-gated transient receptor potential (TRP) channels

Abstract

The molecular basis of the thermal sensitivity of temperature-sensitive channels appears to arise from a specific protein domain rather than integration of global thermal effects. Using systematic chimeric analysis, we show that the N-terminal region that connects ankyrin repeats to the first transmembrane segment is crucial for temperature sensing in heat-activated vanilloid receptor channels. Changing this region both transformed temperature-insensitive isoforms into temperature-sensitive channels and significantly perturbed temperature sensing in temperature-sensitive wild-type channels. Swapping other domains such as the transmembrane core, the C terminus, and the rest of the N terminus had little effect on the steepness of temperature dependence. Our results support that thermal transient receptor potential channels contain modular thermal sensors that confer the unprecedentedly strong temperature dependence to these channels. chimera | temperature gating | temperature jump | thermosensation | pain T he ability to sense temperature is vital to living organisms. In mammals, the neural input on ambient temperature results from specialized groups of neurons that project to the skin. The transducers involve ion channels known as transient receptor potential (TRP) channels (1, 2), which constitute an array of biological thermometers responsive over a broad temperature gradient from noxious cold to noxious hot (3).The molecular mechanism by which temperature changes induce channel opening is not yet known, but the phenomenological tools to analyze the system are known from classical thermodynamic theory. The probability of channel opening follows a Boltzmann relationship to temperature. The enthalpy change (ΔH) between closed and open determines the slope sensitivity of the curve, whereas the entropy change (ΔS) affects its midpoint (T 1∕2 ). The term "threshold" is also commonly used in studies of temperature-sensitive channels to represent the change in temperature required for the response to be larger than the noise level of the recording. Changes in threshold could occur by changes in ∆H or T 1∕2 or the recording noise level.Thermodynamic analyses reveal that thermal TRP channels undergo large enthalpy changes, which accounts for their high temperature sensitivity (4-8). The opening of TRPV1, for example, involves an activation enthalpy of approximately 100 kcal/mol (7), five times the enthalpy change for ligand-or voltage-dependent gating [Q 10 ∼ 2-3 (ref. 9), equivalent to an enthalpy of approximately 20 kcal/mol]. If the free energy change were determined by enthalpy alone, the rate of gating would be very slow because the barrier would be too high. However, thermal TRP channels have evolved to have tightly coupled enthalpy and entropy changes so that the free energy change is relatively small (7). The threshold of activation summarizes the influence of all the temperature-insensitive processes that can regulate gating including the membrane potential (5, 6, 10) and any other allosteric sources such as li...

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

“…The corresponding amino acid, His-378, in the MPR of TRPV1 has been shown to affect the intracellular alkalization-induced activation (60). Yao et al (61) recently reported that MPR might be the heat sensor of TRPVs, as swapping MPRs between TRPV channels led to a switch of the temperature sensitivity. These results suggest MPR is a shared functional element important for the activation of TRPV channels.…”

Cytoplasmic ankyrin repeats of transient receptor potential A1 (TRPA1) dictate sensitivity to thermal and chemical stimuli

“…Does this also apply to other thermosensitive TRP channel family members? A recent study (32) of chimeras between TRPV1 and the high-threshold heat-sensitive channel TRPV2 concluded that heat sensitivity is specified by the linker region connecting the ARD to the transmembrane core. Moreover, the two ARs (AR5 and AR6) most adjacent to this linker region were found to enhance heat sensitivity.…”

“…Deletions within the TRPV1 C terminus have been shown to alter thermal threshold (29), and substitutions or point mutations within the turret or outer pore domain of TRPV1 have been shown to alter heat sensitivity (30,31). Recently, the linker region of TRPV1 connecting the pore-forming transmembrane core to the AR-containing N terminus has been suggested to specify heat sensitivity of the channel (32). However, a consensus view has yet to emerge regarding the mechanism(s) and region(s) that determine TRP channel thermosensitivity, and whether such domains are truly modality-specific regulators of channel function.…”

Low-cost functional plasticity of TRPV1 supports heat tolerance in squirrels and camels

“…Studies in TRPV1 showed that heat sensitivity can be altered by mutations in virtually any channel domain (33,(40)(41)(42)(43)(44)(45)(46), supporting the idea that molecular determinants of the hypothetical heat-sensing module are not localized in a single topologically defined channel element, but are instead distributed throughout the molecule (35). Although a full-length structure of TRPV1 is currently unavailable, the recent cryo-EM structure of TRPA1 revealed tight interations between the N-and C-termini (47), suggesting that topologically distant domains could be functionally coupled, in which case mutations that affect heat sensing or coupling mechanisms could be functionally indistinguishable.…”