The human TRPA1 intrinsic cold and heat sensitivity involves separate channel structures beyond the N-ARD domain
The human TRPA1 (hTRPA1) is an intrinsic thermosensitive ion channel responding to both cold and heat, depending on the redox environment. Here, we have studied purified hTRPA1 truncated proteins to gain further insight into the temperature gating of hTRPA1. We found in patch-clamp bilayer recordings that {Delta}1-688 hTRPA1, without the N-terminal ankyrin repeat domain (N-ARD), was more sensitive to cold and heat, whereas {Delta}1-854 hTRPA1 that is also lacking the S1-S4 voltage sensing-like domain (VSLD) gained sensitivity to cold but lost its heat sensitivity. The thiol reducing agent TCEP abolished the temperature sensitivity of both {Delta}1-688 hTRPA1 and {Delta}1-854 hTRPA1. Cold and heat activity of {Delta}1-688 hTRPA1 and {Delta}1-854 hTRPA1 were associated with different structural conformational changes as revealed by intrinsic tryptophan fluorescence measurements. Heat evoked major structural rearrangement of the VSLD as well as the C-terminus domain distal to the transmembrane pore domain S5-S6 (CTD), whereas cold only caused minor conformational changes. As shown for {Delta}1-854 hTRPA1, a sudden drop in tryptophan fluorescence occurred within 25-20{degrees}C indicating a transition between heat and cold conformations of the CTD, and thus it is proposed that the CTD contains a bidirectional temperature switch priming hTRPA1 for either cold or heat. In whole-cell patch clamp electrophysiology experiments, replacement of the cysteines 865, 1021 and 1025 with alanine modulated the cold sensitivity of hTRPA1 when heterologously expressed in HEK293T cells. It is proposed that the hTRPA1 CTD harbors cold and heat sensitive domains allosterically coupled to the S5-S6 pore region and the VSLD, respectively.