Water coordination near photoactive sites of BR, SRII, and BR_A215T. (a) Snapshot of native BR molecular dynamics simulation taken at ~80 ns. Water molecules (red and white) are localized between retinal and Arg82. (b) Snapshot of native SRII simulation taken at ~80 ns. Water molecules (red and white) are localized near retinal and Arg72, although at least two molecules are seen toward the cytoplasmic region of the protein. (c) Snapshot of BR_A215T mutant simulation taken at ~80 ns. A chain of water molecules (red and white) is visible from the cytoplasmic region above the retinal, and this extends into a region between retinal and Arg82, toward the periplasmic region. This arrangement is not observed in native BR or SRII.