Fba, a novel fibronectin-binding protein from Streptococcus pyogenes, promotes bacterial entry into epithelial cells, and the fba gene is positively transcribed under the Mga regulator

In infection by Streptococcus pyogenes, fibronectin (Fn)-binding proteins p lay important roles as adhesins and invasins. Here, we present a novel Fn-b inding protein of S. pyogenes that exhibits a low similarity to other Fn-bi nding proteins reported. After searching the Oklahoma Streptococcal Genome Sequencing Database for open reading frames (ORFs) with an LPXTG motif, nin e ORFs were found among those recognized as putative surface proteins, and one of them was designated as Fba. The fba gene was found in M types 1, 2, 4, 22, 28 and 49 of S. pyogenes, but not in other serotypes or groups of st reptococci. Fba, a 37.8 kDa protein, possesses three or four proline-rich r epeat domains and exhibits a high homology to FnBPA, the Fn-binding protein of Staphylococcus aureus. Recombinant Fba exhibited a strong binding abili ty to Fn. In addition, Fba-deficient mutants showed diminished invasive cap abilities to HEp-2 cells and low mortality in mice following skin infection . The fba gene was located downstream of the mga regulon and analysis using an mga-inactivated mutant revealed that it was transcribed under the contr ol of the Mga regulator. These results indicate that Fba is a novel protein and one of the important virulence factors of S. pyogenes.