Mechanism and specificity of bacterial two-component signaling systems

Abstract

Bacterial two component signaling (TCS) systems are the predominant means by which bacteria sense and respond to external signals. These systems represent a large family of paralogous proteins; often hundreds of the histidine kinase (HK) and response regulator (RR) pairs that make up a TCS system can be found in a single cell. How do these systems maintain faithful signal transmission and avoid cross-talk? To understand how specificity is determined, we examined co-evolving residues between HKs and RRs, and guided by this, aimed to rewire specificity of several activities of TCS systems. Previous work in the lab has successfully rewired specificity of histidine kinases for response regulators in the phosphotransfer reaction. By mutating different subsets of these co-evolving residues, we were able to rewire specificity of RRs in the phosphotransfer reaction, and partially rewire specificity of HKs and RRs in the phosphatase reaction. Additionally, we identified residues that may dictate specificity between two domains of the histidine kinase, and found that mutating them altered the rate of autophosphorylation. These analyses will allow rational rewiring of two component systems in vivo, and permit us to examine the fitness consequences of this altered specificity, providing insight into the evolutionary pressures on TCS systems.