Kir2 channel bundle crossing gating. (A) PIP₂-KW/GD and PIP₂-KW/GD(G) MD simulated open structures were compared with the closed PIP₂-KW MD simulated structures. Left: Pore-radius profiles of 1-µs PIP₂-KW/GD_MD (purple), 1-µs PIP₂-KW/GD(G)_MD (green), and 100-ns PIP₂-KW_MD (cyan) were computed by HOLE2 with all atoms including side chain, and the averages and standard deviations are shown. Right: The pore-lining surfaces of PIP₂-KW/GD_MD at 1 µs (purple), PIP₂-KW/GD(G)_MD at 1 µs (green), and PIP₂_KW_MD at 100 ns computed by HOLLOW are shown with the major constriction sites designated: SF; HBC (I177, M181); GL, G-loop; and EW. (B) Closed PIP₂-KW crystal structure (cyan) and open PIP₂-KW/GD_MD (purple) structure are overlaid; arrows indicate predominant conformational changes from closed to open state. (B i) TM1 and TM2 helices are shown in ribbon diagram. (B ii) Top-down view of CTDs in ribbon diagram. The central vectors of the C-linker helices projected on the xy-plane are overlaid to show a twisting motion in the inset. (B iii) Side view of CTD in plane of the membrane normal. The central vectors of the C-linker helices projected on the z-axis are overlaid to show a tilting motion in the inset.