Binding of staphylococcal cell surface polysaccharide to human fibrinogen

The interaction between the binding site of a polysaccharide (called compact colony forming active substance (CCFAS)), obtained from the cell surface of a strain of Staphylococcus, and human fibrinogen (HF) was investigated. The CCFAS was found to bind specifically to both the Bβ and γ chains of HF at pH 7.0 and 8.0, and the Aα chain at pH 5.0. The binding of CCFAS with fibrinogen fragments obtained by digestion with plasmin were also investigated. Fragments with Mr of 55 000, 24 000, and 19 000 were the major bands precipitated by CCFAS at pH 7.0 and 8.0. Fragments with Mr of 85 000 and 75 000 bound to CCFAS at pH 5.0. Binding of CCFAS (7 μg) with fibrinogen could be inhibited by 1.2 μg of Bβ chain and 1.5 μg γ chain at alkaline pH or 6.2 μg of the Aα chain at pH 5.0. CCFAS was, therefore, assumed to be specifically bonded with HF molecules, in the alkaline range at least, resulting in compact colony forming activity in serum soft agar and paracoagulation. Key words: cell surface, polysaccharide, Staphylococcus aureus, fibrinogen.