Du EJ and Kang K (2020), A Single Natural Variation Determines Cytosolic...

XB-ART-57193

Mol Cells 2020 Jun 30;436:572-580. doi: 10.14348/molcells.2020.0036.

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A Single Natural Variation Determines Cytosolic Ca2+-Mediated Hyperthermosensitivity of TRPA1s from Rattlesnakes and Boas.

Du EJ , Kang K .

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Transient receptor potential ankyrin 1 from rattlesnakes (rsTRPA1) and boas (bTRPA1) was previously proposed to underlie thermo-sensitive infrared sensing based on transcript enrichment in infrared-sensing neurons and hyper-thermosensitivity expressed in Xenopus oocytes. It is unknown how these TRPA1s show thermosensitivities that overwhelm other thermoreceptors, and why rsTRPA1 is more thermosensitive than bTRPA1. Here, we show that snake TRPA1s differentially require Ca2+ for hyper-thermosensitivity and that predisposition to cytosolic Ca2+ potentiation correlates with superior thermosensitivity. Extracellularly applied Ca2+ upshifted the temperature coefficients (Q10s) of both TRPA1s, for which rsTRPA1, but not bTRPA1, requires cytosolic Ca2+. Intracellular Ca2+ chelation and substitutive mutations of the conserved cytosolic Ca2+-binding domain lowered rsTRPA1 thermosensitivity comparable to that of bTRPA1. Thapsigargin-evoked Ca2+ or calmodulin little affected rsTRPA1 activity or thermosensitivity, implying the importance of precise spatiotemporal action of Ca2+. Remarkably, a single rattlesnake-mimicking substitution in the conserved but presumably dormant cytosolic Ca2+-binding domain of bTRPA1 substantially enhanced thermosensitivity through cytosolic Ca2+ like rsTRPA1, indicating the capability of this single site in the determination of both cytosolic Ca2+ dependence and thermosensitivity. Collectively, these data suggest that Ca2+ is essential for the hyper-thermosensitivity of these TRPA1s, and cytosolic potentiation by permeating Ca2+ may contribute to the natural variation of infrared senses between rattlesnakes and boas.

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Species referenced: Xenopus
Genes referenced: ank1 trpa1

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	Fig. 1. Extracellularly applied divalent cations increase thermosensitivities of TRPA1s from infrared-sensing snakes.(A-I) Representative temperature-dependent current recordings and Q10 scanning analyses of rsTRPA1 (A-C), bTRPA1 (D-F), and dTRPA1 (G-I) in Xenopus oocytes. Upper trace: current recordings at 1 Hz at –60 mV. The extracellular divalent cation conditions are indicated. Middle: temperature change, ~0.5°C/s. The two sets of data points of currents and temperatures producing the maximum Q10 in the recordings are marked with colored circles linked between upper and middle panels. Bottom: Q10 changes throughout the tested temperature range calculated with the interval of 2.5°C. Peak Q10s and Peak Q10-yielding temperatures are indicated. (J) Dot plots of maximum Q10s in the log scale with indicated TRPA1s and extracellular divalent cation conditions. (K) Dot plots of temperatures exhibiting the maximum Q10s (peak temperatures). (L) Dot plots of peak current amplitudes of indicated experiments. P < 0.05 and **P < 0.001, Tukey’s test. # P < 0.05, Dunn’s test.
	Fig. 2. Intracellular Ca2+ chelation suppresses Ca2+-dependent hyperthermosensitivity of rattlesnake TRPA1.(A-C) Dot plots of LogQ10ps (A), peak temperatures (B), and current amplitudes (C) of rsTRPA1 with extracellular Ca2+ at 0.8 mM. Chelators were microinjected into oocytes to be at 1 and 2.5 mM for BAPTA and EGTA in the cytosol. (D-F) Dot plots of LogQ10ps (D), peak temperatures (E), and current amplitudes (F) of rsTRPA1 with extracellular Ba2+ at 0.8 mM indicated conditions. Chelators were microinjected as done in Figs. 2A-2C. (G) Cells with small current amplitudes were compared as BAPTA/Ba2+ experiments yielded low amplitudes (F). (H and I) Thermosensitivities and associated parameters of cells expressing bTRPA1 (H) or dTRPA1 (I) were not affected by BAPTA microinjection. (J) Overexpression of calmodulin WT and the CaM1234 mutant did not change rsTRPA1 thermosensitivity. (K-M) Short (K) and long (L) application of 1 µM thapsigargin did not activate rsTRPA1 before temperature ramps or shift its thermosensitivity. Letters indicate statistically distinct groups (Tukey’s test): P < 0.01 (A), P < 0.001 (D). ***P < 0.001, Tukey’s test; # P < 0.05, Dunn’s test.
	Fig. 3. The conserved cytosolic Ca2+-binding domain is required for Ca2+-dependent potentiation of rsTRPA1 thermosensitivity.(A) Sequence alignment of the conserved Ca2+-binding domain sequence previously identified in human TRPA1 (red line) with those of snake and fruit fly TRPA1s. Gray and black lines mark ankyrin repeats. Gray arrowheads: acidic residues previously characterized to be important for Ca2+ binding. Black arrowheads: acidic residues tested in this study. (B) Scheme for location of the conserved Ca2+-binding domain in the secondary structure of TRPA1. (C-H) Typical Q10 analyses of rsTRPA1 variants with varying extracellular divalent cation conditions as indicated. Peak Q10s and peak temperatures are presented as numbers. (I) Summary of thermosensitivities exhibited by cells expressing indicated rsTRPA1 variants. *P < 0.05, Tukey’s test; # P < 0.05, Dunn’s test.
	Fig. 4. A rattlesnake-imitating substitution in the putative cytosolic Ca2+-binding domain permits bTRPA1 to be potentiated by cytosolic Ca2+.(A and B) Representative temperature-sensitive current recording and Q10 scanning of bTRPA1 WT (A) and bTRPA1 K475D (B). (C) Extracellularly applied Ca2+ raised thermosensitivity of bTRPA1 K475D higher than that of bTRPA1 WT. (D) Comparison of fold Q10 increases by extracellular Ca2+ among bTRPA1s and rsTRPA1. (E) Substantial portion of extracellularly applied Ca2+-dependent thermosensitivity is via the cytosol as probed with BAPTA, but unobservable with extracellularly applied Ba2+. Letters mark statistically different groups (Tukey’s test): P < 0.01 (C), P < 0.05 (E).

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