Diversity of regulatory strategies for two-component system response regulators in bacteria

Abstract

Two-component systems (TCS), composing of a histidine kinase (HK) and a cognate response regulator (RR), are the most important signal transduction devices employed by bacteria to sense and response to a variety of environmental cues. Upon receiving a physical or chemical signal, the sensor HK is activated and then phosphorylates its cognate RR. As the terminal of TCS signal transduction system, RR typically consists of a highly-conserved N-terminal receiver domain (REC) and avariable C-terminal effector domain (ED). In the typical TCS, phosporylated RRs with the enhanced DNA-binding ability, could directly regulate transcriptional levels of the target genes in the form of homodimers. However, the regulatory strategies of RRs are actually more complex and diverse. First, phosphorylation of RRs sometimes induces their detachment from the target DNA, and different RRs also could form heterodimers. Then, except for the DNA-binding domain, the effector module also could be the RNA-binding, protein-binding or catalytic domain. Finally, some RRs only consist of single receiver domains. In this review, we present the recent advances in the different regulatory strategies of RRs, which expands our knowledge on the complexity and flexibility of response action for TCS signal transduction system.