O'Seaghdha, Maghnus 1 , Carina J. van Schooten 2 , Steven W. Kerrigan 3 , Jonas Emsley 4 , Gregg J. Silverman 5 , Dermot Cox 3 , Peter J. Lenting 2 and Timothy J. Foster 1, 2006. FEBS Journal 273:4831-4841.
1 Microbiology Department, Moyne Institute of Preventive Medicine, Trinity College, Dublin, Ireland
2 Laboratory for Thrombosis and Haemostasis, Department of Clinical Chemistry and Haematology, University Medical Center, Utrecht, the Netherlands
3 Department of Clinical Pharmacology, Royal College of Surgeons in Ireland, Dublin, Ireland
4 School of Pharmacy, Centre for Biomolecular Sciences, University of Nottingham, UK
5 Rheumatic Disease Core Center, Department of Medicine, University of California San Diego, La Jolla, CA, USA
Protein A (Spa) is a surface-associated protein of Staphylococcus aureus best known for its ability to bind to the Fc region of IgG. Spa also binds strongly to the Fab region of the immunoglobulins bearing VH3 heavy chains and to von Willebrand factor (vWF). Previous studies have suggested that the protein A–vWF interaction is important in S. aureus adherence to platelets under conditions of shear stress. We demonstrate that Spa expression is sufficient for adherence of bacteria to immobilized vWF under low fluid shear. The full length recombinant Ig-binding region of protein A, Spa-EDABC, fused to glutathione-S-transferase (GST), bound recombinant vWF in a dose-dependent and saturable fashion with half maximal binding of about 30 nm in immunosorbent assays. Full length-Spa did not bind recombinant vWF A3 domain but displayed binding to recombinant vWF domains A1 and D'-D3 (half maximal binding at 100 nm and 250 nm, respectively). Each recombinant protein A Ig-binding domain bound to the A1 domain in a similar manner to the full length-Spa molecule (half maximal binding 100 nm). Amino acid substitutions were introduced in the GST-SpaD protein at sites known to be involved in IgG Fc or in VH3 Fab binding. Mutants altered in residues that recognized IgG Fc but not those that recognized VH3 Fab had reduced binding to vWF A1 and D'-D3. This indicated that both vWF regions recognized a region on helices I and II that overlapped the IgG Fc binding site.
Note: The HRP-Chicken anti-GST used in this publication was supplied by Gallus Immunotech Inc.