Staphylococcus aureus iron-regulated surface determinant B (IsdB) protein interacts with von Willebrand factor and promotes adherence to endothelial cells

Mariangela J. Alfeo,Pietro Speziale,Karen Vanhoorelbeke,Vincenzo De Filippis,Timothy J. Foster,Anna Pagotto,Giulia Barbieri,Giampiero Pietrocola

doi:10.1038/s41598-021-02065-w

Abstract

Staphylococcus aureus is the cause of a spectrum of diseases in humans and animals. The molecular basis of this pathogenicity lies in the expression of a variety of virulence factors, including proteins that mediate adherence to the host plasma and extracellular matrix proteins. In this study, we discovered that the iron-regulated surface determinant B (IsdB) protein, besides being involved in iron transport and vitronectin binding, interacts with von Willebrand Factor (vWF). IsdB-expressing bacteria bound to both soluble and immobilized vWF. The binding of recombinant IsdB to vWF was blocked by heparin and reduced at high ionic strength. Furthermore, treatment with ristocetin, an allosteric agent that promotes the exposure of the A1 domain of vWF, potentiates the binding of IsdB to vWF. Both near-iron transporter motifs NEAT1 and NEAT2 of IsdB individually bound recombinant A1 domain with KD values in the micromolar range. The binding of IsdB and adhesion of S. aureus expressing IsdB to monolayers of activated endothelial cells was significantly inhibited by a monoclonal antibody against the A1 domain and by IsdB reactive IgG from patients with staphylococcal endocarditis. This suggests the importance of IsdB in adherence of S. aureus to the endothelium colonization and as potential therapeutic target.

Highlights

Staphylococcus aureus is a leading cause of serious diseases such as sepsis and infective e ndocarditis[1]
We further investigated the binding of S. aureus cells to host proteins and discovered that iron-regulated surface determinant B (IsdB) interacts with von Willebrand Factor (vWF) and its expression amplifies the vWF-dependent adhesion of S. aureus to endothelial cells
A 75 kDa vWF-binding protein was detected in material released from cells grown in RPMI (Fig. 1A, lane 1), whereas no significant signal was detected in proteins originating from cells grown in brain heart infusion (BHI) (Fig. 1A, lane 2) suggesting that binding depends on a protein that is induced by iron starvation

Summary

Introduction

Staphylococcus aureus is a leading cause of serious diseases such as sepsis and infective e ndocarditis[1]. The endothelium is a major target of endovascular infection and S. aureus has developed several mechanisms to attach to both endothelial cells lining the heart and blood vessel wall and to the exposed extracellular matrix when the endothelium is damaged For this purpose, the bacterium expresses a repertoire of cell wall-anchored (CWA) surface proteins that mediate adhesion to the tissue s tructures[2,3,4]. VWbp is a multi-domain protein that interacts with a variety of ligands including prothrombin13, fibrinogen[14], fibronectin, and Factor XIII15 This protein binds the A1 domain of vWF via a 26 amino acid sequence located in the C-terminal region[8]. NEAT1 preferentially binds Hb, while NEAT2 is involved in heme extraction from the chains of H b19,20

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Results

Conclusion