Characterization of a Highly Dynamic Region in Trag from the F Plasmid

The Escherichia coli F plasmid is representative of conjugative type IV secretion system for the transmission of mobile DNA elements in bacteria, a contributor to widespread antibiotic resistance. The TraG protein of this system consists of a membrane-bound N-terminal domain and a periplasmic C-terminal domain, denoted TraG*. TraG* is essential in preventing redundant DNA transfer. In the donor cell it interacts with TraN within the outer membrane to facilitate mating pair stabilisation. However, TraG* also interacts with a cognate TraS in the inner membrane of the recipient cell to prevent conjugation when the recipient cell carries the same plasmid. This thesis presents structural studies of TraG*; Thermofluor, circular dichroism and HDX-MS experiments showed N-terminal truncation mutants displayed higher stability and less disordered content relative to full-length TraG*. The 45 N-terminal residues of TraG* were predicted to be highly dynamic, possibly serving as a flexible linker between two independently functioning domains.