Studio e Alterazione delle Interazioni fra Emoglobina ed Emofori di Ceppi MRSA: Approcci in Silico per Progettare Nuovi Antimicrobici

In 2017 Methicillin-Resistant Staphylococcus aureus (MRSA) has been prioritized byWHO as the most threatening among multi-drug resistant Gram-positive superbugs, in terms of mortality, economic burden, treatability and lack of research pipelines, among other criteria [1]. MRSA lineages express Iron-regulated Surface Determinants (Isd) proteins aimed at binding human host hemoglobin (Hb), extracting the heme group and degrading it intracellularly to seize iron: this element is, indeed, essential for bacterial growth and virulence. Among Isd proteins, IsdB and IsdH are responsible for hemoglobin capturing and heme mining [2]. To date, however, the mechanism of heme extraction has not been completely understood and no IsdB/IsdH inhibitor has been developed. The aim of this project is to investigate the interaction between IsdB and hemoglobin by means of in silico methodologies, to get insights on the dynamics of the system, the mechanism of IsdB-Hb interaction and heme extraction, and to provide essential information for new potential antimicrobials. Extensive Molecular Dynamics (MD) simulations (about 1 ms) were run to explore the IsdBHb interaction and identify the key residues involved in the complex formation and in the first steps of heme extraction. In particular electrostatic interactions formed at the IsdB-Hb interface have a key role in stabilizing the transition state, accomplished through a disruption of the F helix of Hb, and in extracting the heme. Concurrently, the most representatives Hb conformations were extracted fromMDtrajectories and used to perform Structure-Based Virtual Screenings (SBVS) of commercial compound libraries, to identify molecules able to interfere with the Hb-IsdB complex formation and, thus, affect the bacteria iron supply. The ligands selected by SBVS were then submitted to docking analyses. The most promising candidates have been purchased and in vitro experiments to verify their activity are currently ongoing. References 1. WHO, Prioritization of pathogens to guide discovery, research and development of new antibiotics for drug-resistant bacterial infections, including tuberculosis. Geneva: World Health Organization, 2017, WHO/EMP/IAU/2017.12. 2. Grigg J. C. et al., The structural basis for hemoglobin capture by the Staphylococcus aureus cell-surface protein, IsdH, J. Inorg. Biochem. 2010, 104 (3), 341-8.