The two-component system includes a histidine kinase protein that receives a signal and transmits it to a partner response regulator protein. The response regulator protein in turn transmits the signal to the target. The signal is transmitted between the histidine kinase and the response regulator via phosphorelay. Specifically, the histidine kinase autophosphorylates (using ATP as the phosphoryl donor ) at a histidine residue in the carboxyl-terminal region (comprising approximatelty 240 amino acids) called the transmitter domain in response to a stimulus, and then transfers the phosphoryl group to an aspartate residue in the amino -terminal region (comprising about 120 amino acids) of the partner response regulator protein called the receiver domain. This activates the response regulator, which transmits the signal to its target. Most of the known phosphorylated response regulators stimulate or repress the transcription of specific genes. ( Exception include P-CheB and P-CheY, which affect the chemotaxis machinery). The signaling pathway also includes a phosphatase that dephosphorylates the response regulator, returning it to the nonstimulated state, where it once again can response regulator, returning it to the nonstimulated state, where it once again can respond to the signal. The phosphatase may be the histidine hinase itself, the response regulator, or a separate protein. Histidine kinases may reside in the membrane or in the cytoplasm, although they are often in the membrane, whereas the response regulators are in the cytoplasm. The histidine kinase need not be the first protein in the signal transduction pathway to respond to the signal. In many systems, signals first interact with protein proteins other than the histidine kinase, and the stimulus is relayed to the histidine kinase.

Summary table of 2-component signaling systems in STD bacteria

Summary of domain analysis

• Domain structures of the histidine protein kinase
  
• Domain structures of the response-regulator proteins
  

Browse the 2-Component systems

This analysis was prepared by Gary Xie, Jian Song, and Staff. Please direct questions concerning this analysis to Gary Xie.