Structural features and mechanical abstraction of the NOMPC ion channel. (A) The NOMPC structure (Jin et al., 2017). The channel is a homotetramer with the N-terminal domain starting at AR 1 in contact with an MT (blue and gray blocks). The four-helix bundle extending up from the MT is 29 ARs long terminating in the linker helices (violet) before moving into the preS1 elbow and first TM helix S1 of the membrane spanning region. Like K_V and Na_V voltage-gated ion channels, the TM domain is composed of six TM segments labeled S1–S6 with the S4–S5 linker (orange) connecting S1–S4 to the pore domain (S5–S6). The S6 inner pore helix, which occludes the pore domain in this closed structure, is connected to the TRP domain (dark blue), a long helix that runs parallel to the membrane on the cytoplasmic side and makes contact with the linker helices and the S4–S5 linker. Adjacent helical chains come into close contact at two points along the length of the helical bundle (#1 and #2). The three consecutive sets of six AR repeats used in our molecular simulations are colored blue (ANK1), red (ANK2), and green (ANK3), and the inset shows a zoomed-in representation of ANK1. The approximate position of the membrane is indicated with black lines. (B) A finite element model of NOMPC. The four chains of the bundle were modeled as cylindrical rods with radius r = 1.0 nm and a shape matching the NOMPC structure in panel A (effective helical radius R = 3.43 nm used for analytic calculations). The C-terminal AR 29 terminates into the TRP region, a rigid plate representing the linker helices and TRP domain. The contact points from panel A are indicated in the model.