More than one tandem repeat domain of the extracellular adherence protein of Staphylococcus aureus is required for aggregation, adherence, and host cell invasion but not for leukocyte activation.

The extracellular adherence protein (Eap) is a multifunctional Staphylococcus aureus protein and broad-spectrum adhesin for several host matrix and plasma proteins. We investigated the interactions of full-length Eap and five recombinant tandem repeat domains with host proteins by use of surface plasmon resonance (BIAcore) and ligand overlay assays. In addition, agglutination and host cell interaction, namely, adherence, invasion, and stimulation of proliferation, were determined. With plasmon resonance, the interaction of full-length Eap isoforms (from strains Newman and Wood 46) with fibrinogen, fibronectin, vitronectin, and thrombospondin-1 was found to be specific but with different affinities for the ligands tested. In the ligand overlay assay, the interactions of five single tandem repeat domains (D1 to D5) of Eap-7 (from strain CI-7) with fibronectin, fibrinogen, vitronectin, thrombospondin-1, and collagen I differed substantially. Most prominently, D3 bound most strongly to fibronectin and fibrinogen. Full-length Eap, but none of the single tandem repeat domains, agglutinated S. aureus and enhanced adherence to and invasion of host cells by S. aureus. Constructs D3-4 and D1-3 (in cis) increased adherence and invasiveness compared to what was seen for single Eap tandem repeat domains. By contrast, single Eap tandem repeat domains and full-length Eap similarly modulated the proliferation of peripheral blood mononuclear cells (PBMCs): low concentrations stimulated, whereas high concentrations inhibited, proliferation. Taken together, the data indicate that Eap tandem repeat domains appear to have distinct characteristics for the binding of soluble ligands, despite a high degree of sequence similarity. In addition, more than one Eap tandem repeat domain is required for S. aureus agglutination, adherence, and cellular invasion but not for the stimulation of PBMC proliferation.