Identification and characterization of a fibronectin-binding protein from Granulicatella adiacens

The interaction of microorganisms with fibronectin plays an important role in infective endocarditis. Granulicatella adiacens is a member of the oral microbiota, formerly known as nutritionally variant streptococci, and is often isolated from endocarditis patients. In the present study we identified a surface protein, designated Cha, which binds to fibronectin, by a plaque hybridization procedure using the cshA sequence as probe, which encodes a fibronectin-binding molecule of Streptococcus gordonii DL1. The cha sequence was highly homologous to cshA and encoded a product of 2351 amino acid residues. The protein comprised a unique sequence in the N-terminal half region. The C-terminal region contained nine complete, and one incomplete, 115-amino acid residue repeat blocks. Among eight strains of nutritionally variant streptococci, three G. adiacens strains and one Abiotrophia defectiva strain carried the cha gene. Heterologous expression studies suggested that Cha adhered to immobilized fibronectin, and that this function was located in the unique region. Recombinant Cha protein also adhered to immobilize fibronectin and partially inhibited adherence of G. adiacens to fibronectin in a dose-dependent manner. These results suggest that Cha is a cell surface protein that mediates adherence of G. adiacens to fibronectin.