s and respond accordingly, central to this are the two component systems . TCS are signal transduction devices found in 17328890 all domains of life, and they are especially widespread in bacteria. These systems regulate diverse responses, including nutrient acquisition, energy metabolism, adapting to environmental cues, complex developmental pathways, and host-pathogen interactions. TCS are typically composed of a transmembrane sensor Histidine Kinase protein and a cytoplasmic transcriptional Response Regu- lator . The transmembrane sensor component harbors at least two domains: an input domain that senses the environmental stimulus and a cytoplasmic transmitter with kinase activity that alters the external stimulus into an adaptive signal by autophosphorylation at a conserved histidine residue. The phosphorylated histidine is the resource for phosphorylation of a conserved aspartic acid residue in the receiver domain of the RR. The phosphorylated RR then mediates the cellular response, usually by differential expression of target genes. The target genes of a particular TCS are customized to the specific signal to which the particular TCS corresponds. This specificity is also reflected by the high specificity of HK and RR pairs. The Cpx envelope stress response is controlled by the TCS consisting of membrane localized sensor kinase CpxA and the regulator CpxR. CpxA is induced by a variety of envelope stresses, all of which are predicted to result in protein misfolding. These 1 CpxAR Confers b-Lactam Resistance include physical, chemical, and biological stresses, misfolded proteins, copper, detergents, and EDTA. Activation of CpxA involves relief of inhibition through proteolysis of the periplasmic protein CpxP, in addition to other events that require the periplasmic sensing domain of CpxA. This leads to a cascade of phosphotransfer events that ultimately causes a build up of phosphorylated CpxR, which functions as a buy GS 4059 transcription factor to activate and, in a small number of cases, repress transcription of target genes. A set of the target genes encodes envelope protein folding and degrading factors, such as the periplasmic protease/chaperone DegP/HtrA, the major disulphide oxidase DsbA and two peptidyl-prolylisomerases PpiA and PpiD. Accordingly, a major role of the Cpx response appears to be to maintain envelope protein folding status in the presence of adverse conditions. Molecular, biological and biochemical analysis of several Cpx signals supports the notion that most signals are specific. Therefore the Cpx system serves as an efficient model system to determine the mechanisms involved in signal transduction by a TCS, ranging from signal integration by the kinase CpxA to the output response by CpxR. Studies have elucidated the different functions displayed by the Cpx system for example in envelope stress 8199874 response system, pilus assembly, type 
III secretion, motility and chemotaxis, adherence, and biofilm development. Furthermore, the Cpx system is required for invasion of host cells in diverse pathogenic bacteria, including Escherichia coli, Salmonella enterica serovar Typhimurium, Shigella sonnei, Yersinia enterocolitica, and Legionella pneumophila. A recent study demonstrated that Xenorhabdus nematophilus requires the Cpx system both to colonize its nematode host and to kill larvae of the tobacco hornworm . Overall, the Cpx system of bacteria is known to be involved in maintenance, adapt and protection of the bacterial envelope in respons
Posted inUncategorized