Direct interaction between sensor kinase proteins mediates acute and chronic disease phenotypes in a bacterial pathogen

Abstract

The genome of the opportunistic pathogen Pseudomonas aeruginosa encodes over 60 two-component sensor kinases and uses several (including RetS and GacS) to reciprocally regulate the production of virulence factors involved in the development of acute or chronic infections. We demonstrate that RetS modulates the phosphorylation state of GacS by a direct and specific interaction between these two membrane-bound sensors. The RetS-GacS interaction can be observed in vitro, in heterologous systems in vivo, and in P. aeruginosa. This function does not require the predicted RetS phosphorelay residues and provides a mechanism for integrating multiple signals without cross-phosphorylation from sensors to noncognate response regulators. These results suggest that multiple two-component systems found in a single bacterium can form multisensor signaling networks while maintaining specific phosphorelay pathways that remain insulated from detrimental cross-talk. Two-component system (TCS) signaling pathways are a major signaling mechanism in bacteria and archaea, and are also found in simple eukaryota and higher plants (Wolanin et al. 2002). These diverse organisms capitalize on TCS pathways to monitor critical external and internal stimuli (including levels of nutrients, concentration of ions and gases, temperature, redox states, and cell density) and translate these signals into adaptive responses. Classical TCS pathways share a conserved core architecture: a homodimerizing histidine kinase protein domain (the ''sensor'') and a cognate receiver domain (the ''response regulator''), coupled mechanistically through a histidine-aspartic acid phosphorelay (Stock et al. 2000). Most cognate sensor response regulator pairs are also linked genetically, encoded by adjacent loci in the chromosome (Alm et al. 2006). Although a single bacterial species can encode up to hundreds of genes specifying TCS pathways, it appears that these systems are insulated against detrimental cross-phosphorylation between sensors and noncognate response regulators (Bijlsma and Groisman 2003;Baker and Stock 2007;Laub and Goulian 2007). The identification of multistep phosphorelays (with intermediary proteins between sensor and regulator) and branched pathways (phosphotransfer between one sensor and multiple response regulators and vice versa) (Laub and Goulian 2007) suggests that TCS pathways have the capacity to form sensitive and complex signaling networks.In contrast to microorganisms with restricted habitats, the genomes of bacteria capable of occupying a number of diverse environments typically contain a disproportionately large number of genes encoding signal transduction and regulatory systems, including TCSs that allow them to sense and respond to a wide range of environmental signals. For opportunistic bacterial pathogens, a number of these systems regulate the expression of genes necessary for transitioning from the environmental reservoir to the host, overcoming innate defense mechanisms and initiating the disease process. The bacterial pathogen ...

Sensor–response regulator interactions in a cross-regulated signal transduction network

“…3). This result is consistent with two distinct hypotheses (Goodman et al, 2009): (A) sensor monomers associate to form heterodimers and (B) sensor homodimers associate to form hetero-oligomers.…”

Sticky Situations: Key Components That Control Bacterial Surface Attachment

“…In contrast, LadS inactivation was found to result in decreased attachment, reduced Psl production, and elevated TTSS expression, suggesting that LadS may function to counteract RetS. While the mode of LadS function remains uncharacterized, RetS has been shown to reduce sRNA expression by interfering with GacS autophosphorylation through the formation of RetS/GacS heterodimers (54). Although the reciprocal LadS/RetS regulation of rsmYZ levels via GacAS provides an elegant model of the regulation of the motile-sessile switch by P. aeruginosa, increasing evi-dence is suggesting that this system is far more complex.…”

Small RNA-dependent Expression of Secondary Metabolism Is Controlled by Krebs Cycle Function in Pseudomonas fluorescens

“…The Gac/Rsm cascade is initiated by the GacS/ GacA two-component system (8,10). At high cell population densities, Pseudomonas species excrete chemically uncharacterized signal molecules that can act as inducers of the Gac/Rsm pathway by favoring phosphorylation of the GacS sensor kinase and hence of the cognate GacA response regulator (11)(12)(13)(14). Activated GacA promotes the transcription of two or three non-coding small RNAs (sRNAs), 4 depending on the species.…”