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Infection and Immunity, August 2008, p. 3824-3831, Vol. 76, No. 8
0019-9567/08/$08.00+0     doi:10.1128/IAI.00405-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The Fibrinogen- and Fibronectin-Binding Domains of Staphylococcus aureus Fibronectin-Binding Protein A Synergistically Promote Endothelial Invasion and Experimental Endocarditis ^,

Department of Fundamental Microbiology, University of Lausanne, Biology Building, CH-1015 Lausanne, Switzerland,¹ Infectious Diseases Department, University Hospital, Dijon, France,² Service of Intensive Care Medicine, Centre Hospitalier Universitaire Vaudois and University of Lausanne, CH-1011 Lausanne, Switzerland³

Received 1 April 2008/ Returned for modification 11 May 2008/ Accepted 24 May 2008

Staphylococcus aureus experimental endocarditis relies on sequential fibrinogen binding (for valve colonization) and fibronectin binding (for endothelial invasion) conferred by peptidoglycan-attached adhesins. Fibronectin-binding protein A (FnBPA) reconciles these two properties—as well as elastin binding—and promotes experimental endocarditis by itself. Here we attempted to delineate the minimal subdomain of FnBPA responsible for fibrinogen and fibronectin binding, cell invasion, and in vivo endocarditis. A large library of truncated constructs of FnBPA was expressed in Lactococcus lactis and tested in vitro and in animals. A 127-amino-acid subdomain spanning the hinge of the FnBPA fibrinogen-binding and fibronectin-binding regions appeared necessary and sufficient to confer the sum of these properties. Competition with synthetic peptides could not delineate specific fibrinogen- and fibronectin-binding sites, suggesting that dual binding arose from protein folding, irrespective of clearly defined binding domains. Moreover, coexpressing the 127-amino-acid subdomain with remote domains of FnBPA further increased fibrinogen binding by 10 times, confirming the importance of domain interactions for binding efficacy. In animals, fibrinogen binding (but not fibronectin binding) was significantly associated with endocarditis induction, whereas both fibrinogen binding and fibronectin binding were associated with disease severity. Moreover, fibrinogen binding also combined with fibronectin binding to synergize the invasion of cultured cell lines significantly, a feature correlating with endocarditis severity. Thus, while fibrinogen binding and fibronectin binding were believed to act sequentially in colonization and invasion, they appeared unexpectedly intertwined in terms of both functional anatomy and pathogenicity (in endocarditis). This unforeseen FnBPA subtlety might bear importance for the development of antiadhesin strategies.

Published ahead of print on 9 June 2008.

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Editor: A. Camilli