PURIFICATION OF A BONE SIALOPROTEIN-BINDING PROTEIN FROM STAPHYLOCOCCUS-AUREUS

Bone sialoprotein (BSP) is selectively bound by Staphylococcus aureus cells isolated from patients suffering from infections of bone and joint tissues [Ryden C., Maxe, I., Franzen, A., Ljungh, A., Heinegard, D. and Rubin, K. (1987) Lancet II, 515]. We now report on the purification of a cell wall protein from Staphylococcus aureus,, strain O24, that possesses affinity for bone sialoprotein. Staphylococcal cell-wall components with capacity to inhibit binding of I-125-labeled BSP to staphylococcal cells were solubilized with LiCl (1.0 M, pH 5.0). Preparative SDS/PAGE and protein-overlay experiments revealed that inhibitory activity present in LiC1 extracts resided in a fraction of polypeptides with M, 75000-110000. Staphylococcal proteins solubilized with LiC1 were chromatographed on a Mono-Q anion-exchange column. Inhibitory activity was eluted at 0.6-0.8 M NaCl and could be further purified by affinity chromatography on BSP-Sepharose. Elution of the affinity matrix with 0.1 M glycine, pH 3.0, specifically eluted inhibitory activity. Analysis by SDS/PAGE revealed a single M(r), 97000 polypeptide in the eluate. The purified M(r), 97000 protein bound BSP in protein-overlay experiments. LiC1 extracts from S. aureus, strain E514 or Staphylococcus epidermidis, strain 7686, both lacking the capacity to bind BSP did not contain the M(r), 97000 protein. Our data demonstrate the presence of a S. aureus cell-surface BSP-binding protein. This protein could be involved in bacterial tropism in osteomyelitis.