Molecular Dissection of Conjugative Transport in Gram-negative Bacteria

Type 4 secretion (T4S) systems mediate transfer of DNA from one bacterium to another in a process called "bacterial conjugation". As a result, T4S systems are crucial players in the spread of antibiotic resistance among bacterial populations.

They also mediate secretion and injection of protein effectors into eukaryotic host cells, and therefore, are important virulence factors in bacterial pathogenesis. This proposal focuses on conjugative T4S systems in Gram-negative bacteria. Conjugation starts with the processing of the DNA at a defined site called the origin of transfer (OriT).

This processing step is executed by a large complex called the relaxosome, containing a protein called the "relaxase", and several accessory proteins.

During processing, the relaxase nicks and covalently attaches to the DNA and it is this ssDNA-protein conjugate that is transported through the T4S system. Prior to transport, donor and recipient cells come together to form a conjugative junction.

Our research goals are the following: i-determine the structure of the relaxosome bound to OriT; ii-trap the ssDNA-protein conjugate within the T4S machinery and solve the structure of this substrate-trapped system in order to elucidate the secretion path; iii- investigate the structure and architecture of conjugative junctions between donor and recipient cells.