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An external sodium ion binding site controls allosteric gating in TRPV1 channels.

Jara-Oseguera A, Bae C, Swartz KJ - Elife (2016)

Bottom Line: Here, we show that external sodium ions stabilize the TRPV1 channel in a closed state, such that removing the external ion leads to channel activation.The binding of a tarantula toxin to the external pore also exerts control over temperature-sensor activation, whereas binding of vanilloids influences temperature-sensitivity by largely affecting the open/closed equilibrium.Our results reveal a fundamental role of the external pore in the allosteric control of TRPV1 channel gating and provide essential constraints for understanding how these channels can be tuned by diverse stimuli.

View Article: PubMed Central - PubMed

Affiliation: Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States.

ABSTRACT
TRPV1 channels in sensory neurons are integrators of painful stimuli and heat, yet how they integrate diverse stimuli and sense temperature remains elusive. Here, we show that external sodium ions stabilize the TRPV1 channel in a closed state, such that removing the external ion leads to channel activation. In studying the underlying mechanism, we find that the temperature sensors in TRPV1 activate in two steps to favor opening, and that the binding of sodium to an extracellular site exerts allosteric control over temperature-sensor activation and opening of the pore. The binding of a tarantula toxin to the external pore also exerts control over temperature-sensor activation, whereas binding of vanilloids influences temperature-sensitivity by largely affecting the open/closed equilibrium. Our results reveal a fundamental role of the external pore in the allosteric control of TRPV1 channel gating and provide essential constraints for understanding how these channels can be tuned by diverse stimuli.

No MeSH data available.


Related in: MedlinePlus

The effect of a change in heat capacity associated with the operation of the temperature-sensor on the predictions of the allosteric gating model.(A) Graph showing how J1(T) (blue) and J2(T) (red) (see model i in Figure 7A) change as a function of temperature when they are associated with a change in heat capacity (dashed curves, parameters in Figure 7—source data 2D) or not (continuous curves, parameters in Figure 7—source data 2A). The vertical dotted black lines denote the range of temperatures in which the experimental data was obtained. (B) Theoretical Po-T relations (dashed black curves) calculated using model i (Figure 6A) with a heat capacity difference associated with the two temperature-dependent transitions governed by J1(T) and J2(T) (see Materials and methods and model parameters in Figure 7—source data 2D). Predictions of model i with temperature-independent changes in enthalpy and entropy (i.e., no change in heat capacity) associated with temperature-sensor function are shown as continuous black curves. Experimental Po-T relations (colored circles, data from Figure 6B) for different external Na+ concentrations are also included.DOI:http://dx.doi.org/10.7554/eLife.13356.027
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fig7s4: The effect of a change in heat capacity associated with the operation of the temperature-sensor on the predictions of the allosteric gating model.(A) Graph showing how J1(T) (blue) and J2(T) (red) (see model i in Figure 7A) change as a function of temperature when they are associated with a change in heat capacity (dashed curves, parameters in Figure 7—source data 2D) or not (continuous curves, parameters in Figure 7—source data 2A). The vertical dotted black lines denote the range of temperatures in which the experimental data was obtained. (B) Theoretical Po-T relations (dashed black curves) calculated using model i (Figure 6A) with a heat capacity difference associated with the two temperature-dependent transitions governed by J1(T) and J2(T) (see Materials and methods and model parameters in Figure 7—source data 2D). Predictions of model i with temperature-independent changes in enthalpy and entropy (i.e., no change in heat capacity) associated with temperature-sensor function are shown as continuous black curves. Experimental Po-T relations (colored circles, data from Figure 6B) for different external Na+ concentrations are also included.DOI:http://dx.doi.org/10.7554/eLife.13356.027

Mentions: The molecular mechanism underlying high-temperature sensitivity in thermo-TRP channels remains unknown. In this regard, it was recently noted that changes in side-chain hydration associated with a protein conformational transition that involves only a few residues could result in moderate changes in ΔCp, which in turn would render that conformational change highly temperature-sensitive (Clapham and Miller, 2011). The applicability of this molecular mechanism for ion channels was recently demonstrated using voltage-gated potassium channels with engineered voltage-sensing domains (Chowdhury et al., 2014). Given the possibility that ΔCp is responsible for the temperature-sensitivity in TRPV1 channels, we tested whether considering a change in heat capacity for both temperature-dependent transitions in model i would have an influence on the behavior of the model and the interpretation of our results. Under this framework, equilibrium constants J(T) with the following form were selected (Clapham and Miller, 2011): , where ΔSo(T0) is the standard entropy change at reference temperature T0, R is the gas constant and T the temperature (in Kelvins). Notably, the fits to the experimental data generated by model i with ΔCp ≠ 0 are indistinguishable from those generated without considering a change in heat capacity (ΔCp = 0) (Figure 7—figure supplement 4B), as long as the respective equilibrium constants J1(T) and J2(T) take similar values in the experimentally explored range of temperatures (Figure 7—figure supplement 4A). No changes in parameters other than those associated with J1(T) and J2(T) were required (Figure 7—source data 2E). Thus, our results are equally compatible with temperature-sensing mechanisms that do or do not invoke changes in heat capacity.


An external sodium ion binding site controls allosteric gating in TRPV1 channels.

Jara-Oseguera A, Bae C, Swartz KJ - Elife (2016)

The effect of a change in heat capacity associated with the operation of the temperature-sensor on the predictions of the allosteric gating model.(A) Graph showing how J1(T) (blue) and J2(T) (red) (see model i in Figure 7A) change as a function of temperature when they are associated with a change in heat capacity (dashed curves, parameters in Figure 7—source data 2D) or not (continuous curves, parameters in Figure 7—source data 2A). The vertical dotted black lines denote the range of temperatures in which the experimental data was obtained. (B) Theoretical Po-T relations (dashed black curves) calculated using model i (Figure 6A) with a heat capacity difference associated with the two temperature-dependent transitions governed by J1(T) and J2(T) (see Materials and methods and model parameters in Figure 7—source data 2D). Predictions of model i with temperature-independent changes in enthalpy and entropy (i.e., no change in heat capacity) associated with temperature-sensor function are shown as continuous black curves. Experimental Po-T relations (colored circles, data from Figure 6B) for different external Na+ concentrations are also included.DOI:http://dx.doi.org/10.7554/eLife.13356.027
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fig7s4: The effect of a change in heat capacity associated with the operation of the temperature-sensor on the predictions of the allosteric gating model.(A) Graph showing how J1(T) (blue) and J2(T) (red) (see model i in Figure 7A) change as a function of temperature when they are associated with a change in heat capacity (dashed curves, parameters in Figure 7—source data 2D) or not (continuous curves, parameters in Figure 7—source data 2A). The vertical dotted black lines denote the range of temperatures in which the experimental data was obtained. (B) Theoretical Po-T relations (dashed black curves) calculated using model i (Figure 6A) with a heat capacity difference associated with the two temperature-dependent transitions governed by J1(T) and J2(T) (see Materials and methods and model parameters in Figure 7—source data 2D). Predictions of model i with temperature-independent changes in enthalpy and entropy (i.e., no change in heat capacity) associated with temperature-sensor function are shown as continuous black curves. Experimental Po-T relations (colored circles, data from Figure 6B) for different external Na+ concentrations are also included.DOI:http://dx.doi.org/10.7554/eLife.13356.027
Mentions: The molecular mechanism underlying high-temperature sensitivity in thermo-TRP channels remains unknown. In this regard, it was recently noted that changes in side-chain hydration associated with a protein conformational transition that involves only a few residues could result in moderate changes in ΔCp, which in turn would render that conformational change highly temperature-sensitive (Clapham and Miller, 2011). The applicability of this molecular mechanism for ion channels was recently demonstrated using voltage-gated potassium channels with engineered voltage-sensing domains (Chowdhury et al., 2014). Given the possibility that ΔCp is responsible for the temperature-sensitivity in TRPV1 channels, we tested whether considering a change in heat capacity for both temperature-dependent transitions in model i would have an influence on the behavior of the model and the interpretation of our results. Under this framework, equilibrium constants J(T) with the following form were selected (Clapham and Miller, 2011): , where ΔSo(T0) is the standard entropy change at reference temperature T0, R is the gas constant and T the temperature (in Kelvins). Notably, the fits to the experimental data generated by model i with ΔCp ≠ 0 are indistinguishable from those generated without considering a change in heat capacity (ΔCp = 0) (Figure 7—figure supplement 4B), as long as the respective equilibrium constants J1(T) and J2(T) take similar values in the experimentally explored range of temperatures (Figure 7—figure supplement 4A). No changes in parameters other than those associated with J1(T) and J2(T) were required (Figure 7—source data 2E). Thus, our results are equally compatible with temperature-sensing mechanisms that do or do not invoke changes in heat capacity.

Bottom Line: Here, we show that external sodium ions stabilize the TRPV1 channel in a closed state, such that removing the external ion leads to channel activation.The binding of a tarantula toxin to the external pore also exerts control over temperature-sensor activation, whereas binding of vanilloids influences temperature-sensitivity by largely affecting the open/closed equilibrium.Our results reveal a fundamental role of the external pore in the allosteric control of TRPV1 channel gating and provide essential constraints for understanding how these channels can be tuned by diverse stimuli.

View Article: PubMed Central - PubMed

Affiliation: Molecular Physiology and Biophysics Section, Porter Neuroscience Research Center, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, United States.

ABSTRACT
TRPV1 channels in sensory neurons are integrators of painful stimuli and heat, yet how they integrate diverse stimuli and sense temperature remains elusive. Here, we show that external sodium ions stabilize the TRPV1 channel in a closed state, such that removing the external ion leads to channel activation. In studying the underlying mechanism, we find that the temperature sensors in TRPV1 activate in two steps to favor opening, and that the binding of sodium to an extracellular site exerts allosteric control over temperature-sensor activation and opening of the pore. The binding of a tarantula toxin to the external pore also exerts control over temperature-sensor activation, whereas binding of vanilloids influences temperature-sensitivity by largely affecting the open/closed equilibrium. Our results reveal a fundamental role of the external pore in the allosteric control of TRPV1 channel gating and provide essential constraints for understanding how these channels can be tuned by diverse stimuli.

No MeSH data available.


Related in: MedlinePlus