Distributed Structures Underlie Gating Differences between the K-in Channel KAT1 and the K-out Channel SKOR

The family of voltage-gated (Shaker-like) potassium channels in plants includes both inward-rectifying (K-in) channels that allow plant cells to accumulate K+ and outward-rectifying (K-out) channels that mediate K+ efflux. Despite their close structural similarities, K-in and K-out channels differ in their gating sensitivity towards voltage and the extracellular K+ concentration. We have carried out a systematic program of domain swapping between the K-out channel SKOR and the K-in channel KAT1 to examine the impacts on gating of the pore regions, the S4, S5, and the S6 helices. We found that, in particular, the N-terminal part of the S5 played a critical role in KAT1 and SKOR gating. Our findings were supported by molecular dynamics of KAT1 and SKOR homology models. In silico analysis revealed that during channel opening and closing, displacement of certain residues, especially in the S5 and S6 segments, is more pronounced in KAT1 than in SKOR. From our analysis of the S4-S6 region, we conclude that gating (and K+-sensing in SKOR) depend on a number of structural elements that are dispersed over this similar to 145-residue sequence and that these place additional constraints on configurational rearrangement of the channels during gating.