Selection of Peptides Binding to the a 5 pl Integrin from Phage Display Library

The asp1 integrin binds fibronectin through the integrin recognition sequence Arg-Gly-Asp (RGD). We have used a 6-amino acid peptide library expressed on filamentous phage to identify peptide ligands for asp1. We found that this integrin selectively binds RGD-containing peptides from the library. Of the 32 different sequences obtained, 28 had the RGD motif, 3 contained sequences related to RGD, and only 1 had a clearly different sequence. One of the RGD-containing phage encoded a potentially cyclic insert CRGDCL. The cyclic peptide GAC*RGDC*LGA (where * denotes cysteines forming a disulfide bond) was 10-fold more efficient than any of the linear RGD-containing hexapeptides in inhibiting the binding of RGD-expressing phage to a6P1 or the attachment of aspl-expressing cells to fibronectin. This peptide also inhibited cell attachment mediated by the a&, a&, and avp6 integrins with about 10-fold higher efficiency than linear GRGDSP. One peptide containing an RGD-related sequence, NGRAHA, was also found to inhibit phage attachment and cell adhesion, especially adhesion mediated by the a,p6 integrin. These results indicate that novel and high affinity ligands for integrins can be isolated from a random peptide library.