Chemical biology of bacterial metal acquisition and homeostasis

Abstract

Metals, such as iron, zinc, and manganese, are required for bacterial function and survival. Bacteria have evolved systems to acquire metals from the environments they inhabit. Pathogenic bacteria must obtain metals from their host and have systems dedicated to liberating and stealing metals from host pools. On the other hand, bacteria in the environment must obtain these nutrients from other organic or inorganic sources. While such metals are essential, in high concentrations, they can be toxic due to their reactive nature and bacteria must also have methods of regulating intracellular concentrations. Staphylococcus aureus is a pathogen of humans and obtains nutrient iron in the form of heme. However, heme is toxic to the bacterium at high concentrations and S. aureus utilizes the HssRS two-component system to sense toxic levels of heme and respond by expressing an efflux pump that alleviates heme toxicity. The specific mechanism by which HssRS senses heme levels is not well understood and a high throughput screen was conducted to identify small molecule activators of HssRS. This project has focused on understanding the mechanisms by which two of the molecules identified from the screen, ‘8882 and ‘3981, activate HssRS. Preliminary work has shown ‘8882 activates HssRS in a heme dependent manner while ‘3981 does not. This project focuses on the elucidation of the mechanisms of action of these molecules by identifying the proteins to which they bind using chemical probes for target identification. In contrast to S. aureus, Streptomyces coelicolor is a nonpathogenic soil bacterium and model actinomycete. Many antibiotics used clinically are derived from actinomycetes and this class of bacteria is recognized as a robust source of bioactive small molecules. The molecule coelichelin, which was proposed from genome data and subsequently identified from culture, is a nonribosomal peptide containing three hydroxamate moieties which strongly bind iron. Progress towards the total synthesis of coelichelin is outlined and future completion of the molecule will allow access to large quantities to be used as a chemical tool for studying metal acquisition pathways.