Models of the structure and gating mechanisms of the pore domain of the NaChBac ion channel

The NaChBac prokaryotic sodium channel appears to be a descendent of an evolutionary link between voltage-gated K_V and Ca_V channels. Like K_V channels, four identical six-transmembrane subunits comprise the NaChBac channel, but its selectivity filter possesses a signature sequence of eukaryotic Ca_V channels. We developed structural models of the NaChBac channel in closed and open conformations, using K⁺-channel crystal structures as initial templates. Our models were also consistent with numerous experimental results and modeling criteria. This study concerns the pore domain. The major differences between our models and K⁺ crystal structures involve the latter portion of the selectivity filter and the bend region in S6 of the open conformation. These NaChBac models may serve as a stepping stone between K⁺ channels of known structure and Na_V, Ca_V, and TRP channels of unknown structure.