Homology model of the N.at-K
3.2 channel on the closed state model of rat K
1.2 proposed by Pathak and colleagues. Panel A. Extracellular view. The pore domains (S5-pore loop-S6) are magenta, the voltage sensor domains (S1–S4) are red and the four residues that bound the non-selective pore are white (His-325) orange (Leu-321) green (Tyr-300) and yellow (Asp-260). The central ion selective pore is indicated by the white arrow while the four proposed non-selective pores are indicated with yellow arrows. Panel B. Closer view of one of the non-selective pores. Portions of the intracellular part of the voltage sensing domain (red) are seen through the pore. Panel C. The surface of the aligned rat Kv1.2 closed state model is represented with a blue mesh, indicating that the gating pore is completely occluded in a typical delayed rectifier channel. Panel D. View of the nonselective pore (green arrow) from the cytoplasmic aspect of the channel protein. Gly-331 is the white surface on the upper right of the panel. Panels E and F. Inter-residue distances in the region of the gating pore in NatKv3.2 (panel E) and rat Kv1.2 (Panel F). It is the combination of a shorter side-chain in Asp-260 with a shorter and more compact His-325 that provides a pore that is sufficiently large to be permeable to hydrated ions (panel E), compared with an occluded pore created by Glu-226 and Arg-294 in delayed rectifier channels (panel F).