Crystal structures of forced open mutant channels. (A) Left: Apo-KW/GD (yellow) and PIP₂-KW/GD (orange) crystal structures are shown in ribbon diagram. For clarity, only two subunits are shown for the side view. The local conformations of the PIP₂ binding site region are shown in the inset, with 2fo-fc electron density contoured at 1 σ. (B) Bottom-up views (in the plane of the membrane) shown in ribbon diagrams with electron densities contoured at 1 σ, with mutant G178D and HBC forming I177 residues drawn explicitly in sticks. (C) Top-down view of each structure in the plane of the membrane shows the HBC region with I177 side chains depicted in balls. (D) Pore-radius profiles of PIP₂-KW (cyan) and PIP₂-KW/GD (orange) crystal structures computed by HOLE2 are shown with backbone atoms (left) or all atoms including side chain (right). Pore-lining surfaces of the PIP₂-KW (cyan) and PIP₂-KW/GD (orange) crystal structures are shown with the major constrictions designated: SF; HBC (I177, M181); GL, G-loop; and EW (vertically aligned to the ribbon diagrams in C). (E) Diagonal Cα distance changes (ΔΔCα = PIP₂-KW/GD[ΔCα] − PIP₂-KW[ΔCα]) in the lateral dimension (the xy plane; left) and vertical movement along the z axis of Cα atoms (right) mapped on a single Kir2 subunit. The color bar shows the ranges of distance change.