Structural and Functional Studies of Protein Nanotubes and F-Plasmid Conjugation
Professor Gerald Audette
Faculty of Science and Engineering
Tuesday, March 26, 2013
C2-361 (Reading Room)
Abstract: The ability to stick to surfaces is an essential capability of bacteria that lets them grow and adapt to various environments. Bacteria routinely produce complex nanoscale structures such as flagella and pili, which are fibre-like protein polymers that are used for motility and surface adherence. These robust protein-based adhesion systems, known as adhesins, are assembled and disassembled rapidly by the cell through highly specialized nanomachines known as secretion systems. Our research focuses on the structural and functional characterization of two important secretion systems: the type II secretion system (T2SS) that assembles the type IV pilus (T4P) in several organisms, and the type IV secretion system (T4SS) of the conjugative F plasmid of E. coli. We have previously shown that engineered type IV pilin monomers from P. aeruginosa strain K122-4 (DK122) into protein nanotubes (PNTs) both in solution and at surfaces. Recent chromatographic, light scattering and mass spectrometric studies show that the DK122 pilin exists in a monomer-dime equilibrium in solution and oligomerizes into fibrils prior to assembling into full-length PNTs through a 3-start mechanism similar to native type IV pili. We also characterize through functional and structural analyses that the assembly of the F-plasmid T4SS. In particular, we identify the regions of the thioredoxin-like TraF that are responsible for protein-protein interactions and F-pilus biogenesis, and the interaction of the proteins TraW and TrbC in assembly of the T4SS pore within the periplasmic space.