Classification of response regulators based on their surface properties
The two-component signal transduction system is a ubiquitous signaling module present in most prokaryotic and some eukaryotic systems. Two conserved components, a histidine protein kinase (HPK) protein and a response regulator (RR) protein, function as a biological switch, sensing and responding to changes in the environment, thereby eliciting a specific response. Extensive studies have classified the HPK and RR proteins using primary sequence characteristics, domain identity, domain organization, and biological function. We propose that structural analysis of the surface properties of the highly conserved receiver domain of RRs can be used to build on previous classification methods. Our studies of the OmpR subfamily RRs in Bacillus subtilis and Escherichia coli reveal a notable correlation between the RR receiver domain surface classification and previous classification of cognate HPK proteins. We have extended these studies to analyze the receiver domains of all predicted RR proteins in the marine-dwelling bacterium Vibrio vulnificus.