Identification of Staphylococcus aureus binding proteins on isolated porcine cardiac valve cells

Infective endocarditis caused by Staphylococcus aureus may be initiated by bacterial binding to cardiac valve cells. We investigated binding of whole S. aureus organisms to preparations of isolated porcine cardiac valve proteins. Cultured endothelial and subendothelial cells were surface labeled with iodine 125. After preabsorption with Escherichia coli, an organism that only rarely causes infective endocarditis, binding of surface proteins to S. aureus was assessed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and subsequent autoradiography. The results showed that cardiac valve endothelial cells expressed a major S. aureus-binding protein with an approximate apparent molecular weight of 120,000. In contrast, cardiac valve subendothelial cells expressed on their surface a single species of binding protein with an approximate apparent molecular weight of 220,000; immunoblot analysis suggested that this protein was fibronectin. We also used radiolabeled S. aureus to probe cellular proteins transferred to nitrocellulose membranes. This technique identified a 125,000 molecular weight protein that bound S. aureus in endothelial cell extracts. We conclude that specific S. aureus binding to cardiac valve cells is mediated by different receptors for endothelial and subendothelial cells.