Mutational trajectories from EnvZ/OmpR to RstB/RstA.
EnvZ and OmpR can be converted by a series of single mutations to harbor the specificity residues found in RstB and RstA, respectively, without disrupting phosphotransfer in intermediate stages. (A) A series of single mutations can convert the specificity of EnvZ to match that of RstB and OmpR to match RstA. Starting with the wild type specificity residues in red text at the top, each subsequent line introduces a single mutation (shown in black text) until both sets of specificity residues have been completely changed. As noted in the text, we treated the loop as a single mutation. As shown in panel B, each kinase-regulator pair listed is capable of phosphotransfer and does not include a regulator that is phosphorylated by CpxA. (B) The complete set of intermediates between wild type OmpR (RLR/PFN) and the quadruple mutant (EVA/TTP) are listed. For wild type EnvZ (TLA), the single mutant EnvZ(TYA), the double mutant EnvZ(TYR), and the triple mutant EnvZ(VYR), the set of OmpR mutants recognized by each kinase are shaded, with a merge of all four at the bottom. Mutants that are phosphorylated by CpxA are listed in grey text, all others in black text. Bold lines connect the mutant series shown in panel A.