FIGURE 6.

Contribution of coupled conformational equilibria to the energetics of RR autophosphorylation reactions. The conformational change of a RR receiver domain from an unphosphorylatable (oval) to a phosphorylatable (starburst) conformation is a rate-limiting step in the RR autophosphorylation reaction. The energetic cost of this conformational change is modulated by RR interdomain interactions. Multiple interdomain orientations and strengths of interaction exist (represented by the dotted lines), with strength of the interdomain interaction correlating directly to the activation free energy (ΔG^‡) of the reaction (dotted arrow). Note that the overall reaction has a favorable free energy change (ΔG° < 0) due to the hydrolysis of the small molecule phosphodonor.