Function of the fibronectin-binding serum opacity factor of Streptococcus pyogenes in adherence to epithelial cells

The serum opacity factor (SOF) of Streptococcus pyogenes is a serotyping tool and pathogenesis factor. Using SOF-coated latex beads in cell adherence assays and antiserum directed against SOF in S. pyogenes-HEp-2 cell adherence inhibition experiments, we demonstrate SOF involvement in the fibronectin-mediated adherence of S. pyogenes to epithelial cells. SOF exclusively targets the 30-kDa N-terminal region of fibronectin. The interaction revealed association and dissociation constants 1 order of magnitude lower than those of other S. pyogenes fibronectin-binding proteins.