Structural Studies of the Receiver Domain of LytR from Staphylococcus Aureus and Interaction Studies of TraW and TrbC from the F Plasmid of Escherichia Coli

The emergence of the multi-drug resistant bacteria and the evolutionary spread of the antibiotic resistance genes have become a great concern to human health. Bacteria use various systems in combination or alone in response to environmental stressors and stimuli to adapt to changing conditions. Such systems include the two-component regulatory system (TCS) and the type IV secretion system (T4SS). Microbes use TCSs to regulate important functions such as sporulation, chemotaxis, as well as autolysis that leads to biofilm formation. In addition, microbes utilize T4SSs to deliver DNA, protein substrates, toxin, and virulence factors, from a donor to a recipient cell. These systems are complex, versatile and have a significant impact to human health as they are a major driving force for infection and the spread of antibiotic resistance. The LytSR TCS from Staphylococcus aureus has been found to regulate murein hydrolase activity and autolysis by controlling the expression of the lrgAB and cidABC genes. LytS is predicted to autophosphorylate upon a membrane potential change, consequently transferring the phosphoryl group to the conserved Asp53 residue on the N-terminal domain of the response regulator LytR, leading to the transcription of lrgAB genes. In this study we present the X-ray crystal structure of the N-terminal domain of LytR in apo form and in complex with beryllium fluoride. The identification of dimerization interface residues can be utilized to predict modes of dimerization and therefore activation of the protein. A second project focuses on a representative of the conjugative T4SSs, is the F plasmid from Escherichia coli, which is responsible for the transfer of virulence and antibiotic resistance genes. Two proteins encoded by the F plasmid, TrbC and TraW, are unique to the F-like plasmids and are essential for the transfer of DNA from a donor cell to a recipient cell but their mechanism and function is not known. Interaction studies of TrbC and TraW, as well as crystallization experiments are reported. These studies suggest that the roles of TrbC and TraW are related, and that their interaction is important for the functional transfer of DNA in the conjugative process.