Article

Structural and functional characterization of the Staphylococcus aureus virulence factor and vaccine candidate FhuD2.

Biochemical Journal (Impact Factor: 4.78). 10/2012; DOI: 10.1042/BJ20121426
Source: PubMed

ABSTRACT Staphylococcus aureus is a human pathogen causing globally significant morbidity and mortality. The development of antibiotic resistance in S. aureus highlights the need for a preventive vaccine. Here we explore the structure and function of FhuD2, a staphylococcal surface lipoprotein mediating iron-uptake during invasive infection, recently described as a promising vaccine candidate. Differential scanning fluorimetry and calorimetry studies revealed that FhuD2 is stabilized by hydroxamate siderophores. The FhuD2-ferrichrome interaction was of nanomolar affinity in surface plasmon resonance experiments and fully Fe3+-dependent. We determined the x-ray crystallographic structure of ligand-bound FhuD2 at 1.9Å resolution, revealing the bilobate fold of class III solute-binding proteins (SBPs). The ligand, ferrichrome, occupies a cleft between the FhuD2 N- and C-terminal lobes. Many FhuD2-siderophore interactions enable the specific recognition of ferrichrome. Biochemical data suggest that FhuD2 does not undergo significant conformational changes upon siderophore binding, supporting the hypothesis that the ligand-bound complex is essential for receptor engagement and uptake. Finally, immunizations with FhuD2 alone or FhuD2 formulated with hydroxamate siderophores were equally protective in a murine staphylococcal infection model, confirming the suitability and efficacy of apo-FhuD2 as a protective antigen, and suggesting that other Class III SBPs might also be exploited as vaccine candidates.

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