Two different genes coding for fibronectin‐binding proteins from Streptococcus dysgalactiae The complete nucleotide sequences and characterization of the binding domains

The binding of Streptococcus dysgalactiae to fibronectin involves fibronetcin‐binding protein(s) present on the bacterial surface. Previously, we reported the cloning of two different genes coding for cell‐wall‐associated fibronectin‐binding proteins from S. dysgalactiae strain S2 [Lindgren, P.‐E., Speziale, P., McGavin, M. J., Monstein, H.‐J., Höök, M., Visai, L., Kostiainen, T., Bozzini, S. & Lindberg, M. (1992) J. Biol. Chem. 267, 1924–1931]. The two genes, fnbA and fnbB, have now been sequenced and the primary amino acid sequences of the two fibronectin‐binding proteins, FnBA and FnBB, have been deduced. The two proteins have predicted molecular masses of 117 kDa and 122 kDa, respectively, and are organized in a similar way. The fibronectin‐binding activities are localized in repeated motifs, 32–37 amino acids long, in the COOH‐terminal regions of the proteins. The two fibronectin‐binding proteins have heterologous amino acid sequences, except for the COOH‐terminal ends which include the fibronectin‐binding repeats. The fibronectin‐binding regions of the genes have been fused to IgG‐binding domains of protein A, utilizing the IgG‐binding capacity of the resulting fusion proteins, to facilitate isolation of the fibronectin‐binding domains.