FIBRONECTIN RECEPTORS FROM GRAM-POSITIVE BACTERIA - COMPARISON OF ACTIVE-SITES

Many parasitic bacteria express fibronectin binding proteins that are located on the cell surface. These proteins may act as adhesins and me diate the adherence of the microorganisms to fibronectin-containing ho st tissues. The ligand binding sites in the fibronectin receptor prote ins from Gram-positive bacteria are composed of unique 37-48 amino aci d long motifs that are repeated 3-4 times. We have now expressed the l igand binding sites of fibronectin receptors from Staphylococcus aureu s, Streptococcus dysgalactiae (two receptors), and Streptococcus pyoge nes as recombinant proteins. The purified recombinant proteins have th e expected molecular weights as indicated by electrospray mass spectro scopy although they migrate abnormally on SDS-PAGE. Each recombinant p rotein effectively inhibited the binding of I-125-labled intact fibron ectin or the N-terminal fibronectin domain to Staphylococcus aureus, S treptococcus dysgalactiae, and Streptococcus pyogenes. The relative in hibitory potency of the different recombinant proteins was similar for all target bacteria and is reflected in their relative affinities for fibronectin. Synthetic peptides corresponding to the repeat units of the ligand binding site of the fibronectin receptor proteins were show n to inhibit the binding of the N-terminal fibronectin fragment to Str eptococcus pyogenes cells. Together with amino acid sequence compariso n, these data demonstrate that the repeat motif of the fibronectin rec eptor of Streptococcus pyogenes conforms to the consensus sequence pre viously reported for the Staphylococcus aureus receptor and to one of the Streptococcus dysgalactiae receptors (McGavin et al., 1993).