Effect of photoadduct relaxation on the electrostatic network connecting symmetry-related chains. (a) The D-state structure is displayed as a black ribbon, and the symmetry-related molecules Asym and Asym2 as light-grey and dark-grey ribbons. (b) The L-state structure is displayed as a green ribbon, and the symmetry-related molecules Asym and Asym2 as split-pea- and forest-coloured ribbons. (c) The D′′-state structure is depicted as a firebrick ribbon and the symmetry-related molecules Asym and Bsym as dark salmon and chocolate, respectively. Negatively and positively charged residues are depicted in red and blue, respectively, and key residues are represented as sticks. The black dashed line highlights the presence of a salt bridge in the D-state and L-state structures.