Thermoring basis for the proton-driven heat activation of a cation-selective channel in myriapods.

Thermo-gated ion channels undergo significant time-dependent structural rearrangements for activation. Although the tertiary noncovalent interaction networks can be constrained as thermorings to explain specific temperature thresholds and sensitivity, the timing of critical intra-subunit and inter-subunit noncovalent interactions unfolding remains poorly understood. Here the tertiary noncovalent interaction networks of the broad-range thermal receptor 1 (BRTNaC1) in myriapods were quantified by the thermoring model to estimate thermal thresholds and structural unfolding sequences. The results showed that the theoretical threshold of the weakest intra-subunit noncovalent interaction in the resting closed state of the D217N/E218Q mutant at low temperature matched the experimental activation threshold. Further, the strong inter-subunit swapping interactions at H352, although weakened before strong acid activation of the native channel below pH 4.5, were absent before weak acid-induced heat activation of the mutant at pH 7. Therefore, the different unfolding sequence from strong inter-subunit interactions to the weakest intra-subunit bridges may be required for proton-driven heat activation of BRTNaC1.