Molecular Interactions of Human Plasminogen with Fibronectin-binding Protein B (FnBPB), a Fibrinogen/Fibronectin-binding Protein from Staphylococcus aureus

Giampiero Pietrocola,Giulia Nobile,Valentina Gianotti,Marta Zapotoczna,Timothy J Foster,Joan A Geoghegan,Pietro Speziale

doi:10.1074/jbc.m116.731125

Giampiero Pietrocola, Giulia Nobile + Show 5 more

Open Access

https://doi.org/10.1074/jbc.m116.731125

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Abstract

Staphylococcus aureus is a commensal bacterium that has the ability to cause superficial and deep-seated infections. Like several other invasive pathogens, S. aureus can capture plasminogen from the human host where it can be converted to plasmin by host plasminogen activators or by endogenously expressed staphylokinase. This study demonstrates that sortase-anchored cell wall-associated proteins are responsible for capturing the bulk of bound plasminogen. Two cell wall-associated proteins, the fibrinogen- and fibronectin-binding proteins A and B, were found to bind plasminogen, and one of them, FnBPB, was studied in detail. Plasminogen captured on the surface of S. aureus- or Lactococcus lactis-expressing FnBPB could be activated to the potent serine protease plasmin by staphylokinase and tissue plasminogen activator. Plasminogen bound to recombinant FnBPB with a KD of 0.532 μm as determined by surface plasmon resonance. Plasminogen binding did not to occur by the same mechanism through which FnBPB binds to fibrinogen. Indeed, FnBPB could bind both ligands simultaneously indicating that their binding sites do not overlap. The N3 subdomain of FnBPB contains the full plasminogen-binding site, and this includes, at least in part, two conserved patches of surface-located lysine residues that were recognized by kringle 4 of the host protein.

Highlights

Staphylococcus aureus colonizes the anterior nares of ϳ25% of the healthy human population [1, 2]
CA-MRSA strains have fewer antibiotic resistance determinants than healthcare-associated methicillin-resistant S. aureus (HA-MRSA); they express a lower level of resistance to ␤-lactams, and they can survive on human skin and cause serious skin and soft tissue infections often requiring hospitalization
We have shown for the first time that sortase A-anchored cell wall-associated proteins are the dominant PLGbinding proteins on the S. aureus cell surface

Summary

Introduction

Staphylococcus aureus colonizes the anterior nares of ϳ25% of the healthy human population [1, 2]. The surface of S. aureus is decorated with proteins that are covalently anchored to the cell wall by sortases. The C-terminal fibronectin binding repeats are unstructured and form a flexible stalk-like region that projects the A domain away from the cell surface. The A domains of FnBPA and FnBPB both bind to elastin, most probably involving dock lock and latch. They can engage in homophilic interactions to form dimers, and when two FnBP molecules on neighboring cells interact, this can lead to cell accumulation during biofilm formation [10]. Surface-bound plasmin enables bacteria to remove opsonins IgG and C3b, to degrade fibrin clots, and to promote bacterial spreading by cleaving tissue components (20 –22)

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