Fluorescence Measurement of Kinetics of CheY Autophosphorylation with Small Molecule Phosphodonors.

The Escherichia coli chemotaxis protein CheY is a model receiver domain containing a native tryptophan residue that serves as a fluorescent probe for CheY autophosphorylation with small molecule phosphodonors. Here we describe fluorescence measurement of apparent bimolecular rate constants for reaction of wild type and mutant CheY with phosphodonors acetyl phosphate, phosphoramidate, or monophosphoimidazole. Step-by-step protocols to synthesize phosphoramidate (K+ salt) and monophosphoimidazole (Na+ salt), which are not commercially available, are provided. Key factors to consider in developing autophosphorylation assays for other response regulators are also discussed.