Fibronectin receptors from Staphylococcus aureus

Fibronectin which is recognized for its ability to mediate substrate adhesion of eucaryotic cells has also been shown to bind to Staphylococcus aureus. A further characterization of the interaction of fibronectin with staphylococci is presented here. The binding of ¹²⁵I-fibronectin to S. aureus, strain Cowan 1, is specific, time-dependent, functionally irreversible, and occurs to both live and heat-killed cells. Furthermore, staphylocci may be saturated with fibronectin at a level which suggests the presence of 250 receptors/cell. A lysate produced by digestion of staphylococcal cells with a bacteriolytic enzyme (lysostaphin) inhibited the binding of ¹²⁵I-fibronectin to bacteria. The lysate was depleted of its inhibitory activity by passage through a column of Sepharose substituted with fibronectin. The inhibitory activity was destroyed when the lysate was incubated with trypsin or pronase, and a lysate prepared from trypsin-treated cells did not have inhibitory activity. These data suggest that the inhibitory activity of the lysate is due to solubilized surface proteins acting as receptors for fibronectin. Staphylococcal mutants that selectively had lost protein A or fibronectin receptors could be isolated, which suggests the presence of fibronectin receptors distinctly different from protein A. Externally ¹²⁵I-labeled proteins from the different mutants were analyzed by affinity chromatography on fibronectin-Sepharose followed by gel electrophoresis. The fibronectin receptor was tentatively identified as a protein with an apparent M(r) = 18,000. This component was found in fibronectin-binding strains but was absent in strains deficient in fibronectin receptors.