FIG. 3.

OmpR/PhoB subfamily winged-helix domains. Gray, ribbon diagram of a representative winged-helix domain that defines the OmpR/PhoB subfamily of response regulators; magenta, recognition helix that binds to the major groove of DNA. Effector domains of DrrB, DrrD (PDB accession code 1KGS [8]), OmpR (1OPC [26]), PhoB (1GXQ [26]), and PhoB bound to DNA (1GXP [5]) were superimposed based on the core region of the protein, defined as the three α helices and six β strands. In all proteins, the two loops flanking the recognition helix exhibit considerable conformational flexibility, as shown in the insets. The α loop of DrrD (dotted line) is disordered.