Abstract: Bacterial conjugation is the fundamental process of unidirectional transfer of plasmid DNAs from a donor cell to a recipient cell through a large dual membrane spanning multi-megaDalton transport apparatus termed as the Type IV Secretion System (T4SS). In this era of rising antimicrobial resistance (AMR) already accounting for 700,000 deaths worldwide, T4SSs are prime targets for inhibitor design strategies aimed at limiting AMR. Conjugative T4SSs can function in two very different modes namely the pilus biogenesis mode and the DNA transfer mode. Structural studies on one of the main components of this secretion system, namely the VirB4 AAA+ ATPase solved in its Apo- form using single particle cryo-EM resulted in the determination of the first near-atomic resolution structure of any known T4SS (Mace & Vadakkepat et al., Nature, 2022). High resolution structure of this ~ 4 MDa assembly from E. coli R388 plasmid elucidates not only how the various proteins of the T4SS come together but also reveals an entirely novel mechanism for pilus biogenesis by bacteria in general, completely different from the mechanism of assembly of any other known pili in bacteria. Furthermore, the recently solved detergent-free structure of the E. coli pKM101 T4SS captures the machinery in its pilus biogenesis state (unpublished) and along-with structure of the R388 T4SS conjugative pilus (unpublished) allows us to visualize the pilus-biogenesis mechanism in unprecedented detail. Determining the architecture of these systems and characterizing the mechanism of bacterial conjugation is an essential first step in curtaining AMR and in the development of new devices that can deliver genes into higher eukaryotic organisms for DNA vaccination and gene therapy.

Meeting ID: 923 1431 2045
Passcode: 878380