IDENTIFICATION OF A STAPHYLOCOCCUS-AUREUS EXTRACELLULAR MATRIX-BINDING PROTEIN WITH BROAD SPECIFICITY

A staphylococcal surface protein capable of binding several extracellu lar matrix glycoproteins was purified as a result of our attempts to i dentify a receptor(s) for bone sialoprotein (BSP) on Staphylococcus au reus cells. Proteins from different staphylococcal strains were solubi lized in sodium lauryl sulfate, separated by polyacrylamide gel electr ophoresis, blotted onto Immobilon P membranes, and probed with I-125-B SP. Several bacterial proteins bound the radiolabeled ligand, and vari ous strains expressed different repertoirs of BSP-binding proteins. Ma jor BSP-binding proteins with apparent M(r)s of 72,000 or 60,000 were present on most strains, and these proteins were further studied. The 72- and 60-kDa proteins were preferentially expressed when bacteria we re cultured in Luria broth compared with when they were cultured on tr yptic soy broth, and the abundance of the proteins could be correlated to an increased I-125-BSP binding. Both the 72-kDa and the 60-kDa pro teins were solubilized by extraction of cells with 1 M LiCl and were p urified by cation-exchange chromatography. Amino acid composition anal ysis of the purified 72-kDa protein indicated a high content of lysine (11.9%) and hydrophobic amino acids (28.0% combined). In Western liga nd blotting (immunoblotting) experiments, the 72-kDa protein bound not only BSP but also radiolabeled fibronectin, fibrinogen, vitronectin, thrombospondin, and, to some extent, collagen. Addition of the purifie d 60-kDa protein to S. aureus cells did not inhibit binding of the dif ferent ligands but in some cases resulted in an augmentation of the bi nding of I-125-ligand. Purified 60-kDa protein could hemagglutinate sh eep erythrocytes at a concentration of 61 mug/ml. The agglutination re action was inhibited by high concentrations of fucose, mannose, or mel ibiose. These data suggest that the purified proteins may serve as bac terial receptors with broad specificity for matrix glycoproteins and t hal the proteins may act as carbohydrate-binding proteins.