Staphylococcus aureus expresses a cell surface protein that binds both IgG and β2-glycoprotein I

The existence of a second IgG-binding protein, protein Sbi, in Staphylococcus aureus has been reported previously. Later data indicated that protein Sbi also bound another serum component. This component has now been affinity-purified on immobilized protein Sbi and identified as beta(2)-glycoprotein I (beta(2)-GPI), also known as apolipoprotein H. The minimal beta(2)-GPI-binding domain was identified by shotgun phage display and the binding was shown to be mediated by a region of 57 amino acids, clearly separated from the IgG-binding domain. It is also shown that protein Sbi, and thus the beta(2)-GPI-binding activity, is expressed on the staphylococcal cell surface at levels varying between strains.