Serum Opacity Factor Is a Streptococcal Receptor for the Extracellular Matrix Protein Fibulin-1*

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American Society for Biochemistry and Molecular Biology

RESUMO

The adhesion of bacteria to host tissues is often mediated by interactions with extracellular matrices. Herein, we report on the interactions of the group A streptococcus, Streptococcus pyogenes, with the extracellular matrix protein fibulin-1. S. pyogenes bound purified fibulin-1 in a dose-dependent manner. Genetic ablation of serum opacity factor (SOF), a virulence determinant of S. pyogenes, reduced binding by ∼50%, and a recombinant peptide of SOF inhibited binding of fibulin-1 to streptococci by ∼45%. Fibulin-1 bound to purified SOF2 in a dose-dependent manner with high affinity (Kd = 1.6 nm). The fibulin-1-binding domain was localized to amino acid residues 457–806 of SOF2, whereas the fibronectin-binding domain is contained within residues 807–931 of SOF2, indicating that these two domains are separate and distinct. Fibulin-1 bound to recombinant SOF from M types 2, 4, 28, and 75 of S. pyogenes, indicating that the fibulin-1-binding domain is likely conserved among SOF from different serotypes. Mixed binding experiments suggested that gelatin, fibronectin, fibulin-1, and SOF form a quaternary molecular complex that enhanced the binding of fibulin-1. These data indicate that S. pyogenes can interact with fibulin-1 and that SOF is a major streptococcal receptor for fibulin-1 but not the only receptor. Such interactions with fibulin-1 may be involved in the adhesion of S. pyogenes to extracellular matrices of the host.

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