Selection of Peptide–Bismuth Bicycles Using Phage Display

Abstract

Cysteine conjugation is widely used to constrain phage displayed peptides for the selection of cyclic peptides against specific targets. In this study, the nontoxic Bi³⁺ ion was used as a cysteine conjugation reagent to cross-link peptide libraries without compromising phage infectivity. We constructed a randomized 3-cysteine peptide library and cyclized it with Bi³⁺, followed by a selection against the maltose-binding protein as a model target. Next-generation sequencing of selection samples revealed the enrichment of peptides containing clear consensus sequences. Chemically synthesized linear and Bi³⁺ cyclized peptides were used for affinity validation. The cyclized peptide showed a hundred-fold better affinity (0.31 ± 0.04 μM) than the linear form (39 ± 6 μM). Overall, our study proved the feasibility of developing Bi³⁺ constrained bicyclic peptides against a specific target using phage display, which would potentially accelerate the development of new peptide–bismuth bicycles for therapeutic or diagnostic applications.