Funds for first year research mandate

Plasmid addiction systems ensure the stable maintenance of low copy number plasmids in bacterial populations. They encode for two proteins, a toxin and its antidote. In the cases where the target of the antidote is known, this invariantly is a enzyme crucial for the overall health of the cells, such as gyrase in the case of the ccd system. Structural information on this important family of proteins is largely lacking. The current project aims at determining the crystal structures of a number of plasmid addiction proteins and their relevant in vivo complexes. Besides the fundamental interest in a protein family largely unexplored by structural biology, it is expected that results from crystallography in at least some cases may lead to suggestions for rational drug design. For example, CcdB (the addiction toxin from the ccd system on plasmid F) poisons gyrase by binding on a site different from those used by important antibiotics, for which resistance is becoming a major problem. Moreover, many bacterial toxins are encoded on plasmids, making the inheritance of such plasmids, mediated by addiction systems, worth studying.
Bacterial pili and the adhesins at the tip of these pili form another group of proteins of medical and veterinarian interest for which important structural data are lacking. The F17 pili are a good model system, as they involve only four proteins. They bind to N-acetylglucosamine-bearing receptors in the guts of cattle. By means of crystallography and site-directed mutagenesis, the molecular basis of carbohydrate specificity of the adhesins will be investigated. In addition, protein-protein interactions within the pilus (pilin-adhesin and pilin-pilin) will be investigated.