Identification and characterization of a novel fibronectin-binding protein on the surface of group A streptococci

Abstract

Understanding the role surface proteins play in the interaction of group A streptococci with epithelial cells is an important step toward the development of new strategies to fight infections. Fibronectin-binding proteins in streptococci and staphylococci have been described as important mediators for adherence to eukaryotic cells. In the present study we describe a new Streptococcus pyogenes fibronectin-binding protein (PFBP). The gene encoding the PFBP protein (pfbp) was identified from an M12 strain genomic library. It encodes a protein of 127.4 kDa which contains the LPXTGX motif characteristic of cell wall-associated proteins in gram-positive organisms and is among the largest surface molecules described for group A streptococci. The pfbp gene is transcribed during cell growth and was present in several class I and II streptococcal strains tested. The deduced amino acid sequence of PFBP exhibits a variable N-terminal region and a conserved C-terminal region when compared to most fibronectin-binding proteins identified from other gram-positive bacteria. The N, terminal region presents a stretch of 105 amino acids with no homology with N-terminal regions of previously described fibronectin-binding molecules, while the C-terminal region contains three repeat domains that share significant similarity with the repeat regions of fibronectin-binding proteins from S. pyogenes, S. dysgalactiae, and S. equisimilis. The PFBP repeated region, when expressed on the surface of S. gordonii, a commensal organism, binds to soluble and immobilized fibronectin. This study also shows that, in addition to pfbp, a second gene homologous with that of protein F1 (which also codes for a fibronectin-binding protein) is transcribed during cell growth in the same S. pyogenes strain.