Fig. 1. T2Cu site in as-isolated Br^2DNiR: SRX v SF-ROX structures.

(A) In the 1.1 Å resolution SRX structure (orange), five waters (W1 to W5) and two conformations of Asp⁹²: proximal (main and distorted) are clearly observed. (B) In one active-site conformation, positions of W1 and W2 at the T2Cu site are correlated with the main proximal conformation of Asp⁹². (C) In alternative conformation, water W3 is correlated with the distorted conformation of Asp⁹². (D) T2Cu site in the 1.3 Å XFEL FRIC structure (magenta) clearly shows two full-occupancy waters (W1 and W2) and Asp⁹² in main proximal conformation only. 2F_o − F_c electron density map, contoured at 1σ level, colored in gray. Water molecules are shown as red spheres, and T2Cu is shown as a blue sphere. Distances for possible bonding are shown as black dashed lines.