Protein A is the von Willebrand factor binding protein on Staphylococcus aureus

Endovascular infection is a highly critical complication of invasive Staphy lococcus aureus disease. For colonization, staphylococci must first adhere to adhesive endovascular foci. Von Willebrand factor (VWF) is a large, mult imeric glycoprotein mediating platelet adhesion at sites of endothelial dam age. Earlier it was demonstrated that VWF binds to and promotes the surface adhesion of S. aureus, prompting this effort to identify the vWF adhesin, In Western ligand assays of S. aureus lysates, staphylococcal protein A (SP A) was recognized by purified vWF. Surface plasmon resonance demonstrated t he binding of soluble vWF to immobilized recombinant protein A with a K-d O f 1.49 x 10(-8) mol/L. Using flow cytometry, the binding of fluorescein iso thiocyanate-labeled vWF to S. aureus was found to be saturable and inhibita ble by unlabeled vWF, antiprotein-A antibodies, or IgG, Isogenic Delta spa: :Tc-r mutants were constructed by the insertion of a tetracycline resistanc e cassette into spa using allelic replacement, and it exhibited decreased b inding of soluble vWF and decreased adhesion to vWF-adsorbed surfaces. The interaction was restored on complementation of the mutants with spa-contain ing plasmid pSPA7235. In conclusion, protein A confers interaction of S. au reus with soluble and immobilized vWF in a newly discovered function charac terizing protein A as a novel member of the staphylococcal surface protein adhesin superfamily and suggesting its potential role in the pathogenesis o f endovascular staphylococcal disease. (Blood. 2000;96: 2149-2156) (C) 2000 by The American Society of Hematology.