Background: Conformational changes in the EIC domain of enzyme I upon ligand binding are thought to regulate the phosphotransfer system by modulating the monomer/dimer equilibrium. Results: Binding of phosphoenolpyruvate shifts a preexisting conformational equilibrium in EIC. Conclusion: Conformational selection provides a direct structural link between ligand binding and dimer affinity. Significance: Isolated EIC is an optimal system for investigating dynamic processes regulating EI.

Ceria (CeO2)‐supported metals are widely used as catalysts because of their exceptional redox properties. Here, we use surface contrast NMR methods to investigate the hydrogenation of phenol by Pd supported on ceria nanoparticles. We show that the rigid and planar binding of phenol to Pd is mediated by a weak and highly mobile association of the small molecule to ceria. Interestingly, while addition of phosphate to the mixture does not perturb the adsorption of phenol on Pd, it destabilizes its interaction with ceria and proportionally decreases the rate of catalytic conversion. Our data provide strong experimental evidence that weak interactions between adsorbate and ceria are catalytically competent and explain the exceptional performance of Pd/CeO2 for reductive conversions under mild reaction conditions.

Enzyme I (EI), the first component of the bacterial phosphotransfer signal transduction system, undergoes one of the largest substrate-induced interdomain rearrangements documented to date. Here, we characterize the perturbations generated by two small molecules, the natural substrate phosphoenolpyruvate (PEP) and the inhibitor α-ketoglutarate (αKG), on the structure and dynamics of EI using NMR, small-angle X-ray scattering (SAXS) and biochemical techniques. The results indicate unambiguously that the open-to-closed conformational switch of EI is triggered by complete suppression of micro- to millisecond dynamics within the C-terminal domain of EI. Indeed, we show that a ligand-induced transition from a dynamic to a more rigid conformational state of the C-terminal domain stabilizes the interface between the N- and C-terminal domains observed in the structure of the closed state, thereby promoting the resulting conformational switch and autophosphorylation of EI. The mechanisms described here may be common to several other multidomain proteins and allosteric systems.