Synthetic peptide analogs mimicking a repeated motif within the Staphylococcus aureus fibronectin receptor inhibit binding of the bacteria to fibronectin (Signäs, C., Raucci, G., Jonsson, K., Lindgren, P. E., Anantharamaiah, G. M., Höök, M., and Lindberg, M. (1989) Proc. Natl. Acad. Sci. U.S.A. 86, 699-703). In this study, we have further localized the fibronectin-binding determinant within the 37 amino acid D3 peptide. Chemical modification of the carboxyl side chains of the glutamic and aspartic residues in D3 abolished fibronectin-binding activity, whereas modifications of lysine or tyrosine residues had little effect. An active peptide encompassing residues 15-36 was isolated from a trypsin digest of D3, and a synthetic peptide S16-36 had activity comparable with that of intact D3. Scrambling the amino acid sequence of S16-36 or replacing the aspartic and glutamic residues with asparagine and glutamine resulted in loss of activity. Therefore, one or more of the acidic residues are essential for activity. However, additional sequence is required. Reduction in the size of S16-36 from either the N- or C-terminal end resulted in peptides with greatly diminished activity. These data suggest that the amino acids essential for binding fibronectin are contained within residues 21-33 of the D3 peptide and that the flanking N- and C-terminal amino acids are necessary for the peptide to acquire a conformation that is favorable for fibronectin binding.
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