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

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.