Staphylococcus aureus expresses a cell surface protein that binds both IgGand beta(2)-glycoprotein I

The existence of a second IgG-binding protein, protein Sbi, in Staphylococc us aureus has been reported previously. Later data indicated that protein S bi 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-b inding domain was identified by shotgun phage display and the binding was s hown to be mediated by a region of 57 amino acids, clearly separated from t he 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 a t levels varying between strains.