Thermoring basis for the proton-driven heat activation of a sodium channel in myriapods

Thermo-gated ion channels undergo significant time-dependent structural rearrangements for activation. Although the tertiary noncovalent interaction network 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. This study examined the thermoring structures of the broad-range thermal receptor 1 (PRTNaC1) in myriapods with or without the D217N/E218Q mutations at low and high temperatures. The results showed that the calculated melting threshold of the weakest intra-subunit noncovalent interaction in the resting closed state of the mutant at low temperature matched the experimental activation threshold. However, disrupting this intra-subunit interaction alone did not activate the wild type channel until the strong inter-subunit swapping interactions at H352 were also disrupted by the D217N/E218Q mutations or protonation at pH 6. Therefore, the thermostability of key intra-subunit and inter-subunit interactions dictates their unfolding sequence during thermo-gated activation. (146 words)