Bacterial antibiotic resistance: structure, mechanism and inhibition of ABC transporters responsible for drug efflux and cell wall biogenesis.

Bacterial diseases impose a terrible burden of suffering and death throughout the world but for the past 70 years antibiotics have shielded us from the worst. However, we now face serious peril as the development of antibiotic resistance may, in the words of recent Chief Medical Officer Professor Dame Sally Davies, "kill us before climate change." Increased resistance threatens to revert modern healthcare to a pre-antibiotic era where minor infections become life threatening and even routine surgical procedures carry significant risk. The severity of the problem is acknowledged globally by the World Health Organization, which has initiated coordinated efforts to address this global emergency, which unchecked will lead to millions of premature deaths. Bacteria like E. coli and Salmonella are surrounded by a complex cell envelope consisting of two lipid membranes, which provides a formidable barrier to the entry of many antibiotics. Resistance to antibiotics is further established by dedicated membrane machineries that recognise antibiotics and eject them from the cell before they have an opportunity to act. These drug efflux pumps are composed of three separate components: an inner transporter protein (of which three different classes exist) which recognizes and passes drugs to a TolC "trash chute" open to the cell exterior, and a critical adaptor protein which controls the assembly of this molecular machine. Our laboratory has over 30 years built a research program tackling the molecular mechanisms by which bacteria exhibit antibiotic resistance. We have succeeded in describing the atomic structure and action of the TolC exit duct, and the adaptor proteins. We have also atomically defined their interactions with each other, and the transporter component in the most widespread class of these efflux pumps. This culminated in the first precise atomic view of a complete assembled multidrug efflux pump, provided insight into how it opens to allow expulsion, and how this might be inhibited. More recently, we described the structure of a previously uncharacterised transporter component of a pump revealing a novel structure and atypical mechanism of drug efflux. A related, but distinct, transporter acting in concert with chaperone proteins uses the same architecture to transport lipoproteins, vital components of the protective cell envelope, to the outer membrane. Without this system functioning properly, bacteria cannot survive, making it an attractive target for therapeutic intervention. We seek a continuation of funding for our work, to study these related transporters in drug efflux and lipoprotein transport. By understanding how they recognise the molecules they transport and interact with their partner proteins we will develop a better understanding of the molecular mechanisms by which bacteria resist antibiotics and raise the possibility of counteracting them.