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

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. In the present paper we explore the structure and function of FhuD2 (ferric-hydroxamate uptake D2), 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 iron(III)-dependent. We determined the X-ray crystallographic structure of ligand-bound FhuD2 at 1.9 Å (1 Å=0.1 nm) resolution, revealing the bilobate fold of class III SBPs (solute-binding proteins). 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.

• Authors: Paolo Mariotti, Enrico Malito, Marco Biancucci, Paola Lo Surdo, Ravi P N Mishra, Vincenzo Nardi-Dei, Silvana Savino, Mikkel Nissum, Glen Spraggon, Guido Grandi, Fabio Bagnoli, Matthew J Bottomley
• Journal: The Biochemical journal (Biochem J) Vol. 449 Issue 3 Pg. 683-93 (Feb 01 2013) ISSN: 1470-8728 [Electronic] England
• PMID: 23113737 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• Antigens, Bacterial
• Bacterial Proteins
• Ferric Compounds
• Hydroxamic Acids
• Membrane Transport Proteins
• Periplasmic Binding Proteins
• Siderophores
• Staphylococcal Vaccines
• Transferrin
• Virulence Factors
• iron (III) hydroxamate
• Ferrichrome

Topics

• Animals
• Antigens, Bacterial (chemistry, genetics)
• Bacterial Proteins (chemistry, genetics, immunology, metabolism)
• Crystallography, X-Ray
• Ferric Compounds (metabolism)
• Ferrichrome (metabolism)
• Genes, Bacterial
• Humans
• Hydroxamic Acids (metabolism)
• Membrane Transport Proteins (chemistry, genetics, immunology, metabolism)
• Mice
• Models, Molecular
• Periplasmic Binding Proteins (chemistry, genetics, immunology, metabolism)
• Protein Stability
• Siderophores (metabolism)
• Staphylococcal Vaccines (chemistry)
• Staphylococcus aureus (genetics, immunology, metabolism, pathogenicity)
• Static Electricity
• Transferrin (metabolism)
• Virulence
• Virulence Factors (chemistry, genetics, immunology, metabolism)