Structure of TrwB, a gatekeeper in bacterial conjugation

Bacterial conjugation implies a trans-membrane passage of DNA, mediated by proteins encoded in conjugative plasmids. This results in a spread of genet ic information, including antibiotic resistance acquisition by pathogens. S pecial cases of conjugation are trans-kingdom gene transfer from bacteria t o plants or fungi, and even bacterial sporulation and cell division. One of the main actors in this process is an integral inner membrane DNA-binding protein, called TrwB in the E. coli R388 conjugative system. It is responsi ble for coupling the single-strand DNA to be transferred from the donor to the acceptor cell in its complex with other proteins, with a type IV secret ion system making up the mating apparatus. The TrwB protomer consists of tw o domains: a nucleotide-binding domain of alpha/beta topology, similar to R ecA and DNA ring helicases, and an all-alpha domain. The quaternary structu re reveals an almost spherical homohexamer, strikingly similar to F-1-ATPas e. A central 20 Angstrom wide channel traverses the hexamer, thus connectin g cytoplasm with periplasm. (C) 2001 Elsevier Science Ltd. All rights reser ved.