Figure 2. Overall Structures of Prokaryotic Na_V Channels.

(a) Structure of the Na_VAb bacterial Na_V channel determined at 2.7Å resolution and viewed from the extracellular side [9]. The four subunits of the homotetrameric channel are shown in different colors. The central pore is surrounded by four VSMs. (b) Side view of Na_VAb with the same coloring scheme as shown in (a). S5 and S6 helices of one subunit (slate) and the VSM of another subunit (cyan) are omitted for clarity. (c) Architecture of the Na_VAb pore with pore volume shown in grey and the high-strength-field (HSF) site residue Glu177 shown in sticks. P and P2 indicate the P and P2 helices. (d) Cross-section of the Na_VAb pore showing the closed activation gate. The selectivity filter is shown with electrostatic surface potential colored from −50 to 50 kT (red to blue). (e) Superposition of Na_VRh and Na_VAb with their PMs superimposed [9, 11]. The VSM of the two channels packs against the PM at different angles. (f) Structure of the Na_VMs pore module [13]. (g) Cross-section of the Na_VMs pore showing the open conformation of its activation gate [18]. The selectivity filter is shown with electrostatic surface potential colored from −50 to 50 kT (red to blue). (h) Structure of the Na_VAe1 pore with well-resolved C-terminal domain forming a four-helix bundle [15].