Fig. 4: Crystal structure of the Deinococcus radiodurans response regulator (DrRR).

a Cartoon representation of the dimeric DrRR and AtRR1 structures (PDB code 5BRJ for AtRR1³⁵). Both response regulators only consist of receiver (REC) domains. The α4–β5–α5 face of each response regulator monomer is shown in orange, and the rest of the protein in blue. Ca²⁺ and Mg²⁺ ions at the active sites, the N- and C-termini, as well as the dimerization helices are marked. In the case of DrRR, the dimer formed by chains A and B is shown. b The active site of DrRR with its Ca²⁺ ions and interacting residues. The localization of the Ca²⁺ ions (green) and their interactions (black dashed lines) differ between the chains. The omit difference (F_o–F_c) map of the Ca²⁺ ions is shown as blue mesh at 5.0σ. The omit maps were calculated for each monomer by repeating the final refinement step without the Ca²⁺ ion and the coordinating water molecules. c Sequence logo derived from 50,000 response regulator sequences. The height of each letter indicates the amount of conservation for the corresponding amino acid (one-letter code). The key DrRR residues are shown above the graph, and the full amino acid sequence of DrRR is given below the graph with the same coloring as in panel (a).