An amber-encoding helper phage for more efficient phage display of noncanonical amino acids.

Using an amber suppression-based noncanonical amino acid (ncAA) mutagenesis approach, the chemical space in phage display can be significantly expanded for drug discovery. In this work, we demonstrate the development of a novel helper phage, CMa13ile40, for continuous enrichment of amber obligate phage clones and efficient production of ncAA-containing phages. CMa13ile40 was constructed by insertion of a Candidatus Methanomethylophilus alvus pyrrolysyl-tRNA synthetase/PylT gene cassette into a helper phage genome. The novel helper phage allowed for a continuous amber codon enrichment strategy for two different libraries and demonstrated a 100-fold increase in packaging selectivity. CMa13ile40 was then used to create two peptide libraries containing separate ncAAs, Nϵ-tert-butoxycarbonyl-lysine and Nϵ-allyloxycarbonyl-lysine, respectively. These libraries were used to identify peptide ligands that bind to the extracellular domain of ZNRF3. Each selection showed differential enrichment of unique sequences dependent upon the ncAA used. Peptides from both selections were confirmed to have low micromolar affinity for ZNRF3 that was dependent upon the presence of the ncAA used for selection. Our results demonstrate that ncAAs in phages provide unique interactions for identification of unique peptides. As an effective tool for phage display, we believe that CMa13ile40 can be broadly applied to a wide variety of applications.