title: The A domain of fibronectin-binding protein B of Staphylococcus aureus contains a novel fibronectin binding site.
abstract: The fibronectin-binding proteins FnBPA and FnBPB are multifunctional adhesins than can also bind to fibrinogen and elastin. In this study, the N2N3 subdomains of region A of FnBPB were shown to bind fibrinogen with a similar affinity to those of FnBPA (2 μM). The binding site for FnBPB in fibrinogen was localized to the C-terminus of the γ-chain. Like clumping factor A, region A of FnBPB bound to the γ-chain of fibrinogen in a Ca(2+)-inhibitable manner. The deletion of 17 residues from the C-terminus of domain N3 and the substitution of two residues in equivalent positions for crucial residues for fibrinogen binding in clumping factor A and FnBPA eliminated fibrinogen binding by FnBPB. This indicates that FnBPB binds fibrinogen by the dock-lock-latch mechanism. In contrast, the A domain of FnBPB bound fibronectin with K(D) = 2.5 μM despite lacking any of the known fibronectin-binding tandem repeats. A truncate lacking the C-terminal 17 residues (latching peptide) bound fibronectin with the same affinity, suggesting that the FnBPB A domain binds fibronectin by a novel mechanism. The substitution of the two residues required for fibrinogen binding also resulted in a loss of fibronectin binding. This, combined with the observation that purified subdomain N3 bound fibronectin with a measurable, but reduced, K(D) of 20 μM, indicates that the type I modules of fibronectin bind to both the N2 and N3 subdomains. The fibronectin-binding ability of the FnBPB A domain was also functional when the protein was expressed on and anchored to the surface of staphylococcal cells, showing that it is not an artifact of recombinant protein expression.
authors.affiliation: Department of Microbiology, Moyne Institute of Preventive Medicine, University of Dublin, Trinity College, Dublin, Ireland.
authors.forename: Fiona M
authors.initials: FM
authors.lastname: Burke
authors.forename: Antonella
authors.initials: A
authors.lastname: Di Poto
authors.forename: Pietro
authors.initials: P
authors.lastname: Speziale
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Foster
mesh_terms: D018829:Adhesins, Bacterial / Q000737:chemistry / Q000378:metabolism*; D001422:Bacterial Adhesion; D001665:Binding Sites; D005340:Fibrinogen / Q000378:metabolism*; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D013212:Staphylococcus epidermidis / Q000378:metabolism*
chemical_list: D018829:Adhesins, Bacterial; D011994:Recombinant Proteins; C078635:fibronectin-binding proteins, bacterial; D005340:Fibrinogen