Isolation of peptides that inhibit binding of basic fibroblast growth factor to its receptor from a random phage-epitope library

Basic fibroblast growth factor (bFGF) is known to bind to its cell-surface receptors with high affinity and in a heparin-dependent manner. In an attempt to predict the receptor recognition site on bFGF we screened phage-epitope libraries with monoclonal antibodies DG2 and DE6, which inhibit bFGF binding to its receptor. On the affinity-isolated phages, we identified several peptide sequences as the putative antibody-binding epitopes on bFGF. The identified library epitopes shared the consensus sequence Pro-(Pro/Ser)-Gly-His-(Tyr/Phe)-Lys, corresponding to two continuous protein sequences of bFGF: Pro-Pro-Gly-His-Phe-Lys and Arg-Thr-Gly-Gln-Tyr-Lys at amino acids 13-18 and 120-125 of bFGF, respectively. Synthetic peptides of the corresponding phage epitopes or of the above bFGF sequences specifically inhibited binding of the antibodies to bFGF, blocked binding of bFGF to its high-affinity receptor, and inhibited basal and bFGF-induced proliferation of vascular endothelial cells at submicromolar peptide concentrations. The potent inhibition of bFGF binding and biological activity by peptides recognized by the antibodies suggests that these sequences are functionally involved in receptor binding and may constitute part of the receptor-binding determinants on bFGF.