Rapid Identification of Small Binding Motifs with High-Throughput Phage Display: Discovery of Peptidic Antagonists of IGF-1 Function Original Research Article

A panel of 22 naı̈ve peptide libraries was constructed in a polyvalent phage display format and sorted against insulin-like growth factor-1 (IGF-1). The libraries were pooled to achieve a total diversity of 4.4 × 1011. After three rounds of selection, the majority of the phage clones bound specifically to IGF-1, with a disulfide-constrained CX9C scaffold dominating the selection. Four monovalently displayed sub-libraries were designed on the basis of these conserved motifs. Sub-library maturation in a monovalent format yielded an antagonistic peptide that inhibited the interactions between IGF-1 and two cell-surface receptors and those between IGF-1 and two soluble IGF binding proteins with micromolar potency. NMR analysis revealed that the peptide is highly structured in the absence of IGF-1, and peptides that preorganize the binding elements were selected during the sorting.