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

Summary: 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 β2-glycoprotein I (β2-GPI), also known as apolipoprotein H. The minimal β2-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 β2-GPI-binding activity, is expressed on the staphylococcal cell surface at levels varying between strains.