Identification of avidin and streptavidin binding motifs among peptides selected from a synthetic peptide library consisting solely of D-amino acids.

Peptides consisting solely of D-amino acids (D-peptides) as opposed to their L-counterparts (L-peptides) are resistant towards proteolytic degradation in the organism and may therefore be useful in future efforts to develop new stable peptide-based drugs. Using the random synthetic peptide library technique several L- and D-peptides, capable of binding to both avidin and streptavidin, were found. The L-peptides contained the previously described HPQ/M motifs, and among the D-peptides three binding motifs could be identified, of which the most frequently found one contained an N-terminal aliphatic hydrophobic amino acid (V, L or I) and an aromatic amino acid (Y or F) on the second position. At the third position in this motif several different amino acid residues were found, although N was the most frequent. Peptides representing two of the D-motifs were synthesized as well as peptides containing the HPQ/M motifs, and their binding properties were examined. Although the D-peptides were originally selected using avidin they also inhibited binding between immobilized biotin and soluble streptavidin as well as avidin. The IC50 of some of the peptides were approximately 10(5) times higher than the IC50 for biotin but some had a lower IC50 than iminobiotin. The D-peptides, which were originally selected from the library using avidin, could also inhibit the binding between streptavidin and biotin. Likewise, L-peptides selected from a library screened with streptavidin, could inhibit the binding of both streptavidin and avidin to immobilized biotin. Furthermore, the D-peptide, VFSVQSGS, as well as biotin could inhibit binding of streptavidin to an immobilized L-peptide (RYHPQSGS). This indicates that the biotin-like structure mimicked by these two seemingly very different peptides may react with the same binding sites in the streptavidin molecule.