Autophosphorylation and transphosphorylation mechanisms in bacterial two component systems

Abstract

Two-component signaling circuits (TCS) allow bacteria to detect environmental cues and to produce adaptive responses. These signaling systems are based on autophosphorylation and phosphoryl-group transfers between histidine and aspartate containing sensor kinase and response regulator proteins. Upon reception of a specific stimulus the sensor kinase protein autophosphorylates, by either an inter- or intra-molecular reaction, and transphosphorylates its cognate response regulator, which, typically, acts as a transcriptional regulator, thereby triggering physiological responses. Frequently, in the absence of the stimulus, the sensor kinase proteins are responsible for the dephosphorylation of their cognate response regulators. Furthermore, a group of sensor kinases have additional functional domains that are involved in a forward phosphorelay for signal transmission and in a reverse phosphorelay for signal decay. As is the case of the autophosphorylation reaction, the phosphoryl-group transfers involved in the forward and reverse phosphorelay can occur either intra- or inter-molecularly. In this review, we highlight some important features of bacterial TCS, with special emphasis on the autophosphorylation and phosphoryl-group transfer events.