Tharp, J. M. et al. Nat. Commun. 11, 1392 (2020).

Noncanonical amino acids can be used to expand the chemical space of peptides and proteins. However, their use in phage display has been limited by the fact that Escherichia coli harboring clones with nonsense codons do not grow as well as those with only sense codons. Tharp et al. have developed an approach to bypass this limitation. Their approach exploits a phenomenon called superinfection immunity, in which an infected bacterium becomes resistant to further infection by the same type of phage. After library preparation intended to introduce one amber codon per clone, the library was expressed in cells. Cells harboring clones without an amber codon were able to express an additional surface protein that prevented them from being superinfected with a second phage used for selection, allowing those harboring in-frame amber codons to be further enriched. The researchers used their approach to develop peptides containing butyryllysine that bind and inhibit the protein SIRT2.