Thermosensitive TRP channel pore turret is part of the temperature activation pathway

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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...

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confidence: 99%

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confidence: 99%

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

Yao

Liu

Feng

2011

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“…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.…”

Section: Discussionmentioning

confidence: 99%

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

Laursen

Schneider

Merriman

et al. 2016

The ability to sense heat is crucial for survival. Increased heat tolerance may prove beneficial by conferring the ability to inhabit otherwise prohibitive ecological niches. This phenomenon is widespread and is found in both large and small animals. For example, ground squirrels and camels can tolerate temperatures more than 40°C better than many other mammalian species, yet a molecular mechanism subserving this ability is unclear. Transient receptor potential vanilloid 1 (TRPV1) is a polymodal ion channel involved in the detection of noxious thermal and chemical stimuli by primary afferents of the somatosensory system. Here, we show that thirteen-lined ground squirrels (Ictidomys tridecemlineatus) and Bactrian camels (Camelus ferus) express TRPV1 orthologs with dramatically reduced temperature sensitivity. The loss of sensitivity is restricted to temperature and does not affect capsaicin or acid responses, thereby maintaining a role for TRPV1 as a detector of noxious chemical cues. We show that heat sensitivity can be reengineered in both TRPV1 orthologs by a single amino acid substitution in the N-terminal ankyrin-repeat domain. Conversely, reciprocal mutations suppress heat sensitivity of rat TRPV1, supporting functional conservation of the residues. Our studies suggest that squirrels and camels co-opt a common molecular strategy to adapt to hot environments by suppressing the efficiency of TRPV1-mediated heat detection at the level of somatosensory neurons. Such adaptation is possible because of the remarkable functional flexibility of the TRPV1 molecule, which can undergo profound tuning at the minimal cost of a single amino acid change.TRPV1 | thermosensation | thirteen-lined ground squirrel | bactrian camel | sensory physiology T he somatosensory system allows animals to distinguish between innocuous and noxious temperatures, guiding them to environments most amenable for life and reproduction. In general, mammals avoid contacting surfaces heated more than 40°C, which helps stave off the danger of tissue damage, but at the same time limits inhabitable areas. Mammalian extremophiles such as camels and diurnal rodents, including ground squirrels and chipmunks (Fig. 1A), thrive under thermal conditions that are harmful or even fatal to other animals. The mechanism(s) that allows such species to cope with high temperatures are complex and involve various organs and tissues, including thermoregulatory and somatosensory systems (1-5), but the exact molecular adaptations remain enigmatic.In rodents, noxious stimuli, including temperature, are detected in the skin by the terminal endings of C-type nociceptors from dorsal root or trigeminal ganglia marked by the expression of the heat-activated ion channel transient receptor potential vanilloid 1 (TRPV1) (6-9). Deletion of Trpv1 in mice does not abolish pain sensitivity in general (10) but diminishes sensitivity to noxious temperatures more than 50°C (7,8). Whereas the general pathways of heat sensitivity in standard laboratory rodents has been worked out in some...

“…What remains unknown is the relative amplitude of these currents to the capsaicin-induced current from the same cell. In our mouse TRPV1 replacement mutant, there was a tiny heat response [figure 3b of our original report (4)] that, compared to the capsaicin-induced current, represents a very low open probability. The most straightforward interpretation of this phenomenon is that temperature activation is impaired.…”

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confidence: 99%

Reply to Yao et al.: Is the pore turret just thermoTRP channels’ appendix?

Yang

Cui

Wang

et al. 2010

Self Cite

Numerous studies of thermosensitive transient receptor potential (thermoTRP) channels have focused on the outer pore that contains sites critical for the channel's sensitivity to temperature, acidification, spider toxin, and other gating modulators (Fig. 1). Two segments of each subunit contribute to the outer pore structure: one is between S5 and the pore helix, the other is between the selectivity filter and S6. For the convenience of discussion, we call them the large turret and the small turret, respectively. From the available structural information of tetrameric channels, it is expected that the two turrets interact extensively. Indeed, the sites affecting gating spread across the outer pore landscape. Of particular interests are a number of sites that when mutated, lead to permanent opening or closing of the temperature-activation gate (1-3).In agreement with these findings, our study demonstrated that the large turret is part of the temperature-activation pathway (4). This conclusion is based on experimental results that provided thermodynamic, functional, and structural information. Yao and colleagues (5) question our interpretation of one of these experiments, in which changing the large turret structure by sequence replacement yielded functional channels with no apparent temperature gating. Because the mutant channels exhibited near-normal permeation properties and capsaicin activation, structural perturbation is not nonspecific but limited to the temperature gating process-that is to say, the large turret is important for temperature gating. This interpretation is consistent with the observation that site-directed fluorescence recordings revealed large turret movement during heat activation but not capsaicin activation (4).Yao and colleagues object to this interpretation because they recorded temperature-induced whole-cell currents from a rat TRPV1 deletion mutant of a very similar region of the large turret (5). What remains unknown is the relative amplitude of these currents to the capsaicin-induced current from the same cell. In our mouse TRPV1 replacement mutant, there was a tiny heat response [figure 3b of our original report (4)] that, compared to the capsaicin-induced current, represents a very low open probability. The most straightforward interpretation of this phenomenon is that temperature activation is impaired. Interestingly, reduction in heat response was previously reported by the same group in mutant channels generated from the deletion background (6). They noticed "a large irreversible reduction of the capsaicin current after heating." The selective impairment of temperature sensitivity observed in both our study and that of Yao et al. (6) may be mechanistically related.One important but often overlooked issue is that the activity of all ion channels (as well as nonchannel proteins) exhibit temperature sensitivity. The universal temperature-dependence of channel gating, having a Q 10 value ranging from 3 to 7 in most cases, reflects a gain in kinetic energy upon heating that favors p...