Fig. 4.

Crystal structure of the G77A mutant in 300 mM sodium chloride. The G77A structure solved in the presence of 300 mM NaCl at 2.05-Å resolution (PDB is 6PA0). A 2Fo-Fc electron-density map (light blue, contoured at 2.6 σ) validates the SF structural model colored in yellow. One Na⁺ ion is bound to the S4 site by the carboxyl group of Thr⁷⁵ (presented as magenta spheres). Two small positive electron densities were modeled as water molecules (represented as small green spheres).