Regulation of bacterial phosphorelay systems

In terms of biomass, bacteria are the most successful organisms on earth. This is partly attributed to their tremendous adaptive capabilities, which allows them to sense and rapidly organise responses to changing environmental stimuli. Using complex signalling mechanisms, bacteria can relay cellular information to fine-tune their metabolism, maintain homeostasis, and trigger virulence processes during infection. Across all life, protein phosphorylation represents the most abundant signalling mechanism, which is controlled by a versatile class of enzymes called protein kinases and their cognate phosphatases. For many years, histidine kinase (HK)-containing two-component systems (TCSs) were considered the canonical instruments of bacterial sensing. However, advances in metagenomics has since proven that bacterial phosphorelay is in fact orchestrated by a functionally diverse array of integrated protein kinase types, including Ser, Thr, Tyr and Arg-targeting enzymes. In this review, we provide an up-to-date appraisal of bacterial kinase signalling, with an emphasis on how these sensing pathways are regulated to modulate kinase output. Finally, we explore how selective kinase inhibitors may be exploited to control infections and combat the looming health emergency of multidrug resistant bacteria.