Figure 6: Sketch of the OmpF channel. (a) Longitudinal cross-section. (b) Idealized cross-section of the OmpF channel eyelet for the wild-type (OmpF-WT) protein channel and the mutants with residues Asp113 and Glu117 replaced with cysteines (OmpF-CC) or arginines (OmpF-RR). The dashed contour line represents the hypothetical binding site for a divalent cation based on the atomic structure of OmpF-WT in 1 M MgCl2 [38].