Identification and characterization of a new protein from Streptococcus pyogenes having homology with fibronectin and fibrinogen binding proteins.

Abstract

Fibronectin and fibrinogen-binding proteins have been described as possible adhesin in streptococci and staphylococci. Recent published data has demonstrated that Protein F, a fibronectin-binding protein from group A streptococci, is important in adherence to respiratory cells (8). Other similar proteins already described (i.e. SOF, Sfb and SfbII) are able to competitively inhibit the binding of fibronectin to S. pyogenes (9,10,5). Similarly, clumping factor from S. aureus, is known to promote adherence to fibrinogen-coated surfaces (7). When the sequence from SFFBP-12 was compared against all the others fibronectin and fibrinogen-binding proteins described in streptococci and staphylococci (1-10), an identity at the amino acid level, ranging from 38 to 69% was found for the C region. For the repeated region (R), the identity ranged between 47 and 75%. Unlike all the other proteins already described in group A streptococci, the protein we describe here, SFFBP-12, shares a high degree homology (67-75%) with the fibronectin-binding protein B from S. dysgalactiae (6), as well as homology with the S. aureus clumping factor (7) and fibronectin-binding protein B (3), making it a new potential fibronectin-fibrinogen binding protein for group A streptococci. These characteristics would also imply that SFFBP-12 contains two different fibronectin-binding domains (regions B and C), thus enhancing its role as a possible major adhesin molecule. RNA transcription assays showed a transcript with the expected molecular size for the intact SFFBP-12 protein, confirming that the protein is actively expressed during bacterial growth. SFFBP-12 is the largest protein of its kind identified from group A streptococci and is comparable in size to the fibronectin binding protein B from S. dysgalactiae (6). If it is shown that SFFBP-12 does in fact bind both fibronectin and fibrinogen, as the sequence data suggest, it would make this molecule a major virulence determinant for the group A streptococcus.