Part:BBa_K4645012

The RstAB system is a bacterial two-component regulatory system consisting of the membrane sensor

The RstB/RstA system is a ubiquitous TCS composed of the membrane-associated histidine kinase RstB and its cognate response regulator RstA. In Escherichia coli and Salmonella, RstA is under the control of the PhoP/PhoQ TCS, which monitors extracellular Mg2+ levels, and up-regulates the acid-induced asr (acid shock RNA) gene and the biofilm regulator csgD gene under acidic conditions . Overexpression of RstA in Salmonella enterica serovar Typhimurium induced degradation of RpoS and altered biofilm formation. Moreover, RstA directly binds to the promoter of the feo operon in Salmonella and promotes the expression of the iron transporter FeoB under iron-replete conditions [1].

The RstA/RstB system is a bacterial two-component regulatory system consisting of the membrane sensor, RstB and its cognate response regulator RstA.The RstA consists of an N-terminal receiver domain (RD, residues 1–119) and a C-terminal DNA-binding domain (DBD, residues 130–236). Phosphorylation of RstA induces dimerization, which allows two RstA DBDs to bind to a tandem repeat, called the RstA box, and regulate the expression of downstream genes [1]. In the sequence of the acid-sensitive promoter P asr, there is a RstA box [2].

Usage

We constructed this two-component system downstream of the acid-sensitive promoter Pasr to serve as a positive feedback loop enhancing circuit expression.RstB facilitates the phosphorylation of RstA under high proton concentration, which in turn reinforces Pasr promoter through positive feedback, quickly generating a large amount of CI to shut off the antitoxin expression. Since the functioning of the RstAB two-component system also relies on the change of proton concentration, even an extremely low level of leakage from Pasr cannot achieve positive feedback without the pH change, thus avoiding system imbalance due to the positive feedback effect.The circuit is shown in the figure 1.

Figure 1.pH-sensitive pathway, and toxin-antitoxin pathway

Reference

[1]Li YC, Chang CK, Chang CF, Cheng YH, Fang PJ, Yu T, Chen SC, Li YC, Hsiao CD, Huang TH.Structural dynamics of the two-component response regulator RstA in recognition of promoter DNA element. Nucleic Acids Res. 2014 Jul;42(13):8777-88.

[2]Ogasawara H, Hasegawa A, Kanda E, Miki T, Yamamoto K, Ishihama A. Genomic SELEX search for target promoters under the control of the PhoQP-RstBA signal relay cascade. J Bacteriol. 2007 Jul;189(13):4791-9.