The two-component signal transduction systems of Pseudomonas aeruginosa
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Two-component signal transduction systems are important components for bacteria, because they allow the bacteria to sense environmental conditions and rapidly adapt to changes in the environment. Two-component systems generally contain a sensor histidine kinase, which detects an environmental signal and responds by autophosphorylation at a histidine residue using ATP as the phosphate donor. The phosphate group is then transferred to an aspartate residue in the receiver domain of the second component, the response regulator, which in its activated form responds by stimulating or repressing gene expression or motility, as needed for the physiological responses of the cell. The structural versatility of two-component systems reflects the wide range of signals to which bacteria respond. Despite this versatility, histidine kinases and response regulators show a conserved mechanism of signal transfer. Pseudomonas aeruginosa is a versatile organism that can use a variety of nutrient sources and is found in many different environments. It is a human pathogen in nosocomial infections as well as in pulmonary fluid of patients with cystic fibrosis. P. aeruginosa encodes genes for over 60 two-component regulatory systems. In this review, I discuss the structure and function of two-component systems in bacteria, and conduct a phylogenetic analysis of the P. aerugionsa two-component systems. Finally, I develop a model of the calcium-responsive two-component system of P. aeruginosa, PA2656/PA2657, which is closely related to the magnesium responsive PmrAB and phosphate responsive PhoPQ two-component systems. The results provide insight on how P. aeruginosa is able to detect and respond to changing environmental conditions.