Goat vitronectin: characterization and binding to Staphylococcus aureus

Vitronectin (Vn) is a multifunctional protein present in plasma and in the extracellular matrix. Previous studies have demonstrated binding of many bacteria to human Vn. In this study, we have characterized goat Vn and studied its interaction with S. aureus considering the importance of this bacterium in animal husbandry. Goat Vn possesses two RGD motifs, at positions 45 and 106, and two multimerization sites that were identified from the recombinant fragments of the protein. The first site was localized at the N-terminus of the protein and the second at the C-terminus that did not require a full heparin-binding region, as partial deletion of this site did not affect multimerization. The 40 kDa N-terminal fragment, Vn1-200, supported S. aureus binding. Similarly, two fragments representing the C-terminus of the protein (35 kDa Vn183-444 and the 22 kDa Vn323-444) with complete heparin-binding site also supported S. aureus binding whereas the 14 kDa fragment, Vn363-444, with truncated heparin-binding site did not. Thus, a complete heparin-binding site at the C-terminus of Vn is essential for S. aureus binding. Maximum S. aureus binding was observed with Vn isolated by immunoaffinity chromatography, which predominantly consisted of multimers. This observation is significant considering the fact that the multimeric Vn is a component of the matrix surrounding the cells and may play an important part in initial bacterial adhesion and subsequent colonization.