The switch between an inactive and active conformation is an important transition for signaling proteins, yet the mechanisms underlying such switches are not clearly understood. Escherichia coli CheY, a response regulator protein from the two-component signal transduction system that regulates bacterial chemotaxis, is an ideal protein for the study of allosteric mechanisms. By using 15N CPMG relaxation dispersion experiments, we monitored the inherent dynamic switching of unphosphorylated CheY. We show that CheY does not undergo a two-state concerted switch between the inactive and active conformations. Interestingly, partial saturation of Mg2+ enhances the intrinsic allosteric motions. Taken together with chemical shift perturbations, these data indicate that the μs-ms timescale motions underlying CheY allostery are segmental in nature. We propose an expanded allosteric network of residues, including W58, that undergo asynchronous, local switching between inactive and active-like conformations as the primary basis for the allosteric mechanism.
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We thank Bob Bourret, Ruth Silversmith, and Bob Immormino for kindly providing the CheY DNA, helpful discussions, and critical reading of the manuscript. We thank Matthew Whitley for his help in the assignments and preparation of BeF x -bound CheY. We also thank Peter Thompson and Austin Smith for their help with analysis of A113P and Y106W mutants. This work was supported by National Institutes of Health (NIH) grant GM066009 (to A.L.L.), and additional support was provided to L.R.M. through NIH training grant GM008570.