Staphylococcus aureus expresses a cel I surface protein that binds both IgG and

The existence of a second IgG-binding protein, protein Sbi, in Staphy/ococcus 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 P,-glycoprotein I (/?,-GPI), also known as apolipoprotein H. The minimal P,-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 P,-GPI-binding activity, is expressed on the staphylococcal cell surface at levels varying between strains