Synthesis and characterization of a stable analog of the phosphorylated form of the chemotaxis protein CheY.

The bacterial chemotaxis protein CheY is activated in vivo by the covalent phosphorylation of a single aspartate residue at position 57. However, this phosphate linkage is unstable (t1/2 approximately 20 s at room temperature), thereby precluding many biochemical analyses. Here we present a synthetic scheme to prepare an analog of CheY-phosphate (Che Y-P) with chemical stability of the phosphate linkage enhanced by several orders of magnitude relative to the native protein. Starting with CheY D57C, a site-specific mutant of CheY with a unique cysteine residue in place of the aspartate at position 57, two sequential disulfide exchange reactions were performed to form the final product 'CheY D57C-SPO3' with a thiophosphate moiety covalently bonded to the protein in a disulfide linkage. Mass spectral analysis showed that the desired analog was present at 70-80% of the total protein. The disulfide linkage had a t1/2 of 8 days at 4 degrees C. Biochemical characterization of CheY D57C-SPO3 included assessment of conformational properties using tryptophan fluorescence, evaluation of metal binding properties and measurement of binding interactions with the chemotaxis proteins CheZ and FliM. Despite possessing a phosphoryl group at a nearly identical location as native CheY-phosphate, the analog was unable to emulate CheY-phosphate function, thereby supporting the idea that there are very precise geometric requirements for successful CheY activation.