Biosynthesis, structure, and function of yersiniabactin, a virulence factor of Yersinia pestis

Siderophores are relatively small, iron chelating molecules produced by many microorganisms and some plants to obtain iron. Siderophores are produced in the earliest stages of infection by non-ribosomal peptide synthase (NRPS)/polyketide synthase (PKS) systems and have been shown to be essential to infection. Siderophores are of interest for many reasons. The NRPS/PKS systems which manufacture siderophores are similar to the systems which produce many other complex molecules such as natural antibiotics. Understanding these systems could lead to combinatorial methods of producing new antibiotics or other biologically active molecules. Siderophores also have great medicinal potential. Siderophores are used to treat iron toxicity, the potency of many common antibiotics has been increased by including elements from siderophores into their structure, and because of the role of siderophores in virulence in many pathogens and similarities between some siderophore-dependent iron transport systems, these molecules are an obvious target for development of new antimicrobial therapies as resistances to traditional antibiotics continue to develop. This research has focused on yersinibactin (Ybt) the siderphore produced by Yersinia pestis .; In this work we report that purified Ybt has been crystallized successfully in the ferric complex form and the crystal structure has been determined. The roles of several enzymes in the NRPS/PKS system that produces Ybt have been explored in further detail. In this work we report how changes to several of these enzymes affect overall siderophore production and shed light onto the overall efficiency of this process. Additionally, in this work we report the biochemical characterization of YbtS, the salicylate synthase of Yersinia pestis that mediates first step in production of the Ybt, and the results of stable isotope experiments aimed at illustrating the first step of this enzyme mechanism in more detail. Thus we propose a mechanism which identifies the source of the initial nucleophile, and show how those results relate to the overall structure and mechanism of anthranilate synthase analogs.