phosphorylation switches

Molecular Mechanisms of Signal Transduction : "The majority of signal transduction in bacteria occurs through pathways known as 'two-component' systems. These systems utilize a common mechanism involving transfer of a high-energy phosphoryl group from a histidine protein kinase to an aspartate residue of a response regulator protein. Response regulator proteins typically contain two domains: a regulatory domain and an effector domain. The regulatory domains of response regulator proteins can be thought of as phosphorylation-activated switches that are turned on and off by phosphorylation and dephosphorylation. In the active, phosphorylated state, the conserved regulatory domains activate effector domains to elicit specific responses such as flagellar rotation, regulation of transcription, or enzymatic catalysis. Phosphorylation alters the conformation of the regulatory domain, and the altered molecular surface is exploited for regulatory protein-protein interactions. " Link to link-to-images.