Antimicrobial resistance (AMR) is responsible for more than 700,000 annual deaths [1]. According to the WHO, there is a high priority need for the development of novel targets and antibacterial treatments for
Staphylococcus aureus, in particular the methicillin-resistant and vancomycin-resistant variants [2].
Almost all living organisms have an absolute need of iron to fulfil a plethora of biological functions. Specifically, S. aureus relies on iron for invading the host and establishing infection, with hemoglobin (Hb) as preferred iron
source. The human host deploys a defense mechanism (nutritional immunity, NI), based on the sequestration of iron and heme, but bacterial pathogens have evolved several strategies to counteract the host
iron-withholding capacity, including siderophores and hemophores. When, during infections, S. aureus secretes hemolysins that break the erythrocyte membrane and release Hb in the bloodstream, bacterial hemophores
scavenge the heme and transport it into the cytoplasm [3]. Heme capture is carried out by the Iron-regulated surface determinants IsdB and IsdH anchored to the cell wall [4, 5]. IsdB and IsdH confer to S. aureus the ability
to escape NI, but a precise understanding of the mechanisms of heme binding and transport, and the involved protein-protein interactions (PPIs), is still missing.
The main aim of this project is to set up a highly multidisciplinary platform to characterize in detail the hemophore-mediated iron acquisition by S. aureus and design small molecules able to inhibit this process, restore the
natural NI and inhibit bacterial growth, thus acting as antimicrobials or antimicrobial enhancers. To our knowledge, no strategy based on the design of ligands targeting and inhibiting hemophore:Hb interaction has been
pursued so far. The X-ray structures of hemophore:Hb complexes [6, 7] set the basis for this innovative approach and already allowed the preliminary identification of PPI inhibitors, through virtual screening campaigns
targeting a surface cleft on Hb, where IsdB and IsdH bind, thus demonstrating the viability of the approach. In parallel, we will also target the SbnA enzyme that catalyzes the first step in the staphyloferrin B siderophore
biosynthesis [8]. SbnA belongs to the PLP-dependent enzymes, a group for which we have already identified and characterized specific inhibitors [9, 10]. Targeting S. aureus iron acquisition at different sites will increase
the chance of success in fighting the current and worrisome AMR. The experimental workflow will include recombinant expression of IsdB, IsdH and SbnA, X-ray scattering spectroscopy, crystallography and cryo-EM to
determine the structure of protein-ligand complexes, computational and synthetic chemistry to identify and develop molecular interferents, and inhibitor testing in vitro, by means of ad hoc developed ELISA assays, Surface
Plasmon Resonance and Atomic Force Spectroscopy, and through biological tests on S. aureus cultures.