Abstract
Bacterial type IV secretion systems translocate virulence factors into eukaryotic cells, distribute genetic material between bacteria, and have shown the potential as a tool for the genetic modification of human cells. They form expansive multi-protein nanomachines that span the entire cell envelope of Gram-negative bacteria. In this seminar, I will describe the electron microscopy reconstruction of the 3 megadalton type IV secretion system encoded by the E.coli R388 conjugative plasmid. The result represents one of the largest single particles yet isolated, and reveals a markedly different architecture to other secretion systems such as the well characterised type III secretion system. Implications for substrate transfer, whether it be an antibiotic resistance cassette or the oncogenic Helicobacter CagA protein, will also be discussed.