Summary of useful methods for two-component system research

Since the discovery of protein phosphorylation in bacterial nitrogen assimilation and chemotaxis more than 30 years ago, many biochemical techniques for the analysis of two-component signal transduction systems have been developed. Over time the experimental conditions to follow the flow of phosphate groups from histidine kinases to the cognate response regulators in vitro have been fine tuned. Several approaches were applied to circumvent the instability of the phosphorylated form of response regulator proteins to analyze the structures of their activated forms. Recently, a FRET (fluorescence resonance energy transfer) assay was developed to monitor interactions of chemotaxis proteins in vivo. The availability of bacterial genome sequence databases has facilitated the identification of two-component systems and enabled prediction of interacting kinase-response regulators pairs.