The ability of bacteria to respond to changes in their surrounding environment is vital for survival. Two-component regulatory systems (TCS) are the primary mechanism that allows microorganisms to respond to external stimuli. This phosphotransfer system functions through the action of two conserved proteins. A sensor histidine kinase and a response regulator protein [1].
Enterococcus faecalis is a gram-positive commensal bacterium of the human intestinal tract and an opportunistic pathogen. The ability of E.faecalis to utilize ethanolamine (abundant in the intestinal tract) as the sole source of nitrogen and carbon provides an advantage for survival and colonization [2]. Ethanolamine metabolism in E.faecalis requires the ethanolamine utilization operon (eut) that is under the TCS regulation of the EutW sensor kinase and EutV response regulator. EutW undergoes autophosphorylation in the presence of ethanolamine and subsequently transfers a phosphate group to EutV (Figure 1A) [3]. Phosphorylated EutV dimerises and binds dual mRNA hairpin sites upstream of genes eutP, eutG, eutS and eutA. EutV binding disrupts the intrinsic terminator hairpin allowing complete transcript production, gene expression and subsequent ethanolamine metabolism [4, 5].
Molecular understanding of how EutV interacts with RNA will further our knowledge of bacterial gene regulation and may provide potential targets for new generation antimicrobials.
To date, EutV along with a phosphor-mimic mutant EutV D54E, have been overexpressed and purified from E.coli. Purified proteins have been shown to be functionally active through binding RNA in REMSA experiments. EutV D54E has been crystallised and a 3Å native data set collected at the Australian Synchrotron.