Evidence for Steric Regulation of Fibrinogen Binding to Staphylococcus aureus Fibronectin-binding Protein A (FnBPA)

Abstract

Background: Staphylococcus aureus fibronectin-binding protein A (FnBPA) binds fibronectin and fibrinogen at adjacent sites.Results: The fibrinogen-binding mechanism is similar but not identical to homologous bacterial proteins. Ternary complex formation by intact fibronectin and fibrinogen on adjacent FnBPA sites could not be demonstrated.Conclusion: Fibrinogen binding is sterically regulated by fibronectin binding.Significance: Steric regulation might result in targeting of S. aureus to fibrin clots.

Two repetitive, biofilm-forming proteins from Staphylococci: from disorder to extension

“…In the tandem β-zipper interaction [27], the disordered Fn-binding repeats bind sequential Fn1 modules by forming an additional extrinsic β-strand along the triple stranded β-sheet; thus the disordered FnBP repeats adopt a highly extended conformation on binding to Fn. A β-zipper interaction is also observed in the interaction of N2N3 with a fibrinogen peptide [21] (Figure 1b). A combination of structural studies and binding studies [21,24,26] have revealed that, while in close proximity in FnBPA (Figure 1a), the fibrinogen-binding site and the most N-terminal Fnbinding repeat (FnBPA-1) do not overlap.…”

“…A β-zipper interaction is also observed in the interaction of N2N3 with a fibrinogen peptide [21] (Figure 1b). A combination of structural studies and binding studies [21,24,26] have revealed that, while in close proximity in FnBPA (Figure 1a), the fibrinogen-binding site and the most N-terminal Fnbinding repeat (FnBPA-1) do not overlap. Nonetheless, Fn binding to FnBPA-1 appears to sterically regulate fibrinogen binding to N2N3 [21].…”

“…A combination of structural studies and binding studies [21,24,26] have revealed that, while in close proximity in FnBPA (Figure 1a), the fibrinogen-binding site and the most N-terminal Fnbinding repeat (FnBPA-1) do not overlap. Nonetheless, Fn binding to FnBPA-1 appears to sterically regulate fibrinogen binding to N2N3 [21]. The C-terminal region of N2N3 and FnBPA-1 appear to cooperate in bacterial invasion of host cells and experimental endocarditis [30]; however, the relationship between the structure and function of this region of S. aureus FnBPA is yet to be fully understood.…”

“…of fibrinogen (Figure 1b) [21] and to elastin [22]; and an intrinsically disordered ∼30 kDa C-terminal repetitive region [23] that binds multiple copies of Fn [24] through a novel mechanism of protein-protein recognition called a tandem β-zipper [25][26][27] (Figure 1c). The two intrinsically disordered regions (N1 and the C-terminal repeats) have higher sequence conservation across S. aureus strains than the folded N2N3 region [28].…”

“…FnBPA (Figure 1a) consists of a 170 amino acid N1 domain at the N-terminus, predicted to be disordered (Andrew Brentnall, personal communication) and not required for biofilm formation [20]; the N2N3 Ig-like domains that bind to the C-terminus of the gamma-chain repeats that bind to sequential N-terminal Fn F1 modules; a C-terminal region containing proline-rich repeats (PRR) and cell wall (W) and membrane (M) spanning region; and a sortase A recognition motif (LPETG) for cell wall crosslinking. (b) A ribbon diagram of the X-ray crystal structure of N2N3 (residues 195-503, green) bound to a fibrinogen peptide (blue) comprising 17 C-terminal residues of the fibrinogen γ A chain (protein data bank (pdb) accession code: 4b60) [21]. (c) Two X-ray crystal structures of, from left to right, fibronectin F1 modules 5 Fn1-4 Fn1 (grey) bound to a peptide (residues 510-528, cyan) from the most N-terminal Fn-binding repeat (FnBPA-1; pdb accession code: 2rky); and 3 Fn1-2 Fn1 (grey) bound to a peptide (residues 529-546, cyan) from FnBPA-1 (pdb accession code: 2rkz).…”