Turning a Kv channel into hot and cold receptor by perturbing its electromechanical coupling.

Abstract

Voltage-dependent potassium channels (Kv) are extremely sensitive to membrane voltage and play a crucial role in membrane repolarization during action potentials. Kv channels undergo voltage-dependent transitions between closed states before opening. Despite all we have learned using electrophysiological methods and structural studies, we still lack a detailed picture of the energetics of the activation process. We show here that even a single mutation can drastically modify the temperature response of the Shaker Kv channel. Using rapid cell membrane temperature steps (Tsteps), we explored the effects of temperature on the ILT mutant (V369I, I372L, and S376T) and the I384N mutant. The ILT mutant produces a significant separation between the transitions of the voltage sensor domain (VSD) activation and the I384N uncouples its movement from the opening of the domain (PD). ILT and I384N respond to temperature in drastically different ways. In ILT, temperature facilitates the opening of the channel akin to a ″hot″ receptor, reflecting the temperature dependence of the voltage sensor ′s last transition and facilitating VSD to PD coupling (electromechanical coupling). In I384N, temperature stabilizes the channel closed configuration analogous to a ″cold″ receptor. Since I384N drastically uncouples the VSD from the pore opening, we reveal the intrinsic temperature dependence of the PD itself. Here, we propose that the electromechanical coupling has either a ″loose″ or ″tight″ conformation. In the loose conformation, the movement of the VSD is necessary but not sufficient to efficiently propagate the electromechanical energy to the S6 gate. In the tight conformation the VSD activation is more effectively translated into the opening of the PD. This conformational switch can be tuned by temperature and modifications of the S4 and S4-S5 linker. Our results show that we can modulate the temperature dependence of Kv channels by affecting its electromechanical coupling.