Controlled opening and closing of an ion-selective pathway in response to changes of membrane potential is a fundamental feature of voltage-gated ion channels. In recent decades, various details of this process have been revealed with unprecedented precision based on studies of prototypic potassium channels. Though current scientific efforts are focused more on a thorough description of voltage-sensor movement, much less is known about the similarities and differences of the gating mechanisms among potassium channels. Here, we describe the peculiarities of the KCNQ1 gating process in parallel comparison to Shaker. We applied alanine scanning mutagenesis to the S4-S5 linker and pore region and followed the regularities of gating perturbations in KCNQ1. We found a fractional constitutive conductance for wild-type KCNQ1. This component increased significantly in mutants with considerably leftward-shifted steady-state activation curves. In contrast to Shaker, no correlation between V(1/2) and Z parameters was observed for the voltage-dependent fraction of KCNQ1. Our experimental findings are explained by a simple allosteric gating scheme with voltage-driven and voltage-independent transitions. Allosteric features are discussed in the context of extreme gating adaptability of KCNQ1 upon interaction with KCNE β-subunits.
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