FIBRONECTIN RECEPTORS FROM STREPTOCOCCUS-DYSGALACTIAE AND STAPHYLOCOCCUS-AUREUS - INVOLVEMENT OF CONSERVED RESIDUES IN LIGAND-BINDING

The nucleotide sequence of two genes encoding fibronectin (Fn) recepto rs FnBA and FnBB of Streptococcus dysgalactiae S2 revealed the presenc e of repeated motifs (called R(A1-A3) and R(B1-B3), respectively) whic h encode Fn binding activity (Lindgren, P.-E., McGavin, M. J., Signas, C., Guss, B., Gurusiddappa, S., Hook, M., and Lindberg, M. (1993) Eur . J. Biochem. 214, 819-827). Synthetic peptides of 32-37 amino acids, corresponding to individual repeated motifs, were assayed for the abil ity to inhibit Fn binding to cells of S. dysgalactiae. Within the R(A) Motifs, peptide A2 was 10-fold more active than either A1 or A3, whil e in the R(B) motifs, only B3 was active. The same level of activity i s observed when these synthetic peptides were assayed for inhibition o f Fn binding to cells of Staphylococcus aureus. Likewise, synthetic pe ptides corresponding to the R(D1-D3) motifs, which comprise a ligand b inding domain in a Fn receptor from S. aureus, inhibit binding of Fn t o both S. aureus and S. dysgalactiae. Assays of chemically modified pe ptides and peptide fragments derived from chemical or proteolytic clea vage suggest that a conserved core sequence, defined as ED(T/S)(X9,10) GG(X3,4)(I/V)DF, within a 30-amino acid-long segment is present in the active R(A) and R(D) motifs. Analyses of the importance of individual residues of this core sequence indicate that the ED(T/S) motif is non essential, whereas the GG and the (I/V)DF together with additional aci dic residues in the C-terminal half of the peptide are required for ac tivity.