Revised Manuscript Received March 16, 1994® abstract: Many parasitic bacteria express fibronectin binding proteins that are located on the cell surface. These proteins may act as adhesins and mediate the adherence of the microorganisms to fibronectincontaining host tissues. The ligand binding sites in the fibronectin receptor proteins from Gram-positive bacteria are composed of unique 37-48 amino acid long motifs that are repeated 3-4 times. We have now expressed the ligand binding sites of fibronectin receptors from Staphylococcus aureus, Streptococcus dysgalactiae (two receptors), and Streptococcus pyogenes as recombinant proteins. The purified recombinant proteins have the expected molecular weights as indicated by electrospray mass spectroscopy although they migrate abnormally on SDS-PAGE. Each recombinant protein effectivelyinhibited the binding of 125I-labeled intact fibronectin or the N-terminal fibronectindomain to Staphylococcus aureus, Streptococcus dysgalactiae, and Streptococcus pyogenes. The relative inhibitory 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 shown to inhibit the binding of the N-terminal fibronectin fragment to Streptococcus pyogenes cells. Together with amino acid sequence comparison, these data demonstrate that the repeat motif of the fibronectin receptor of Streptococcus pyogenes conforms to the consensus sequence previously reported for the Staphylococcus aureus receptor and to one of the Streptococcus dysgalactiae receptors (McGavin et al., 1993).

Fibronectin (Fn) is a dimeric glycoprotein found in high concentrations in the extracellular matrix and body fluids of vertebrates. The primary biological role of Fn appears to be related to the ability of the matrix form of the protein to serve as a substratum for the adhesion of animal cells [for a review, see Yamada (1989)]. Parasitic microorganisms have developed mechanisms that allow them to adhere to and colonize tissues in a host animal, a situation that may provide easier access to nutrients supplied by the host. Some bacteria express surface proteins which serve as Fn adhesins and can mediate the adherence of the bacteria to Fn-containing matrices. The primary amino acid sequences of Fn receptors from