STRUCTURE OF MODULAR EXTRACELLULAR ADHERENCE PROTEIN FROM S AUREUS & COMPLEXES

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Staphylococcus aureus is a widespread, persistent pathogen that causes a broad range of infections in humans and animals. Initiation of S. aureus infections requires a diverse array of virulence-determining factors, including exoenzymes, toxins, and numerous protein adhesins. The Extracellular Adherence Protein (Eap) of S. aureus functions as a secreted virulence factor by mediating interactions between abundant host ligands (e.g. fibrinogen, fibronectin, and vitronectin) and the bacterial cell, and recent genetic and biochemical studies have shown that Eap-mediated protein-protein interactions serve a central role in S. aureus pathogenesis. As a first step toward understanding these medically-important interactions, we recently determined three crystal structures of the repeating domain (EAP domain) present in four copies in the full-length Eap protein. The goal of this project is to expand upon these previous studies of EAP domain structure by determining: (a) the structure of the full-length Eap protein and (b) the biochemical and structural mechanisms that underlie Eap-ligand interactions. The modular nature of Eap and its size (50 kDa) have precluded a thorough structural characterization of the full-length protein by the traditional approaches of NMR and x-ray crystallography. In contrast, small angle X-ray scattering (SAXS) has proven to be an exceedingly valuable tool in determining the structural properties of precisely this type of molecule. The capabilities of SAXS will also allow us to achieve the first structural characterization of several medically-important Eap complexes, including those with a) human Fibrinogen (Fg), b) human Intercellular Adhesion Molecule-1 (ICAM-1), c) human Fibronectin (Fn), and d) the S. aureus cell surface-associated neutral phosphatase (NPase). These studies will further our understanding of several molecular events essential to the infection process and may suggest novel approaches to treating these infections.