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 play important roles as adhesins and invasins. Here, we present a novel Fn-binding protein of S. pyogenes that exhibits a low similarity to other Fn-binding proteins reported. After searching the Oklahoma Streptococcal Genome Sequencing Database for open reading frames (ORFs) with an LPXTG motif, nine 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 streptococci. Fba, a 37.8 kDa protein, possesses three or four proline-rich repeat domains and exhibits a high homology to FnBPA, the Fn-binding protein of Staphylococcus aureus. Recombinant Fba exhibited a strong binding ability to Fn. In addition, Fba-deficient mutants showed diminished invasive capabilities 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 control of the Mga regulator. These results indicate that Fba is a novel protein and one of the important virulence factors of S. pyogenes.