Conservation of the hydrogen-bond network in bacterial response regulators

The bacterial response regulator (RR) superfamily is activated by single aspartyl phosphorylation to modulate a distant target binding surface for diverse functions. The enteric CheY RRs, which represent the chemotaxis subfamily, have been extensively characterized. Their native, chemical or genetically-altered crystal structures have revealed an essential role for water-mediated hydrogen bonds (H-bonds) in activation. Here, we use molecular dynamics (MD) to compare the protein-water H-bond network in basal and in-silico phosphorylated conformations. We supplement the MD with energy frustration profiles for atomic structures and models from selected RR superfamily representatives. The energetically frustrated phosphorylation pocket consists of the conserved aspartate triad for phosphorylation, plus associated structural waters and residues for Mg2+ ion coordination. It orchestrates the H-bond network characterized here in atomic detail. The network has an energetically stable core. Its plastic nodes switch bonding states coupled to loop flexibility and sidechain rotations. Mutual information revealsthat the long-range, dynamic networks respond to single H-bond transitions. The network centrality of the phosphorylation pocket, connected to the target binding surface by water-mediated channels via the conserved switch residues (T87, K109), increases upon phosphorylation. Analysis of other RR representatives suggests this design is a generic feature of RR allostery with subtle, function-dependent differences. The water contribution may prove critical for the design of specific RR sub-family specific, allosteric inhibitors.