Multiple interactions between human vitronectin and Staphylococcus aureus

Multiple interactions between human vitronectin and Staphylococcus aureus strain V8 were observed. An upward-curved Scatchard plot indicated both high-affinity binding (K_d1 = 7.4 · 10^?10 M) with 260 binding sites per bacterial cell and moderate-affinity binding (K_d2 = 7.4 · 10^?8 M) with 5240 copies per cell. Negative cooperativity of this binding was characterized by its Hill coeffiocient of less than unity (0.70 ± 0.08). Up to 60% of the vitronectin-bacteria interaction was unaffected by high ionic strength (i.e., 2.4 M NaCl), and was not inhibited by highly-charged heparin oligosaccharides. Various oligosaccharides (4–20 monosaccharide units) generated by partial deaminative cleavage of heparin were found to affect vitronectin binding to S. aureus. Short-chain-length oligosaccharides increase and long oligosaccharides inhibit vitronectin binding, in accordance with direct association of these saccharides with multimeric vitroectin. A protein having a molecular mass of 60 kDa was identified as a putative high-affinity staphylococcal vitronectic-binding protein. These results indicate that interaction of multimeric vitronectin, mostly present at extracellular matrix sites with multiple recognition sites on the S. aureus surface, may contribute to bacterial colonisation.