Genetically encoded, phage-displayed cyclic peptide library and methods of making the same
Embodiments of the present disclosure pertain to methods of selecting cyclic peptides that bind to a target by transforming a phage display library with a plurality of nucleic acids into bacterial host cells, where the nucleic acids include phage coat protein genes with a combinatorial region that encodes at least one cysteine and at least one non-canonical amino acid. The transformation results in the production of phage particles with phage coat proteins where the cysteine and the non-canonical amino acid couple to one another to form a cyclic peptide library. Phage particles are then screened against the desired target to select bound cyclic peptides. Amino acid sequences of the selected cyclic peptides are then identified. Additional embodiments pertain to methods of constructing a phage display library that encodes the cyclic peptides. Further embodiments of the present disclosure pertain to the produced cyclic peptides, phage display libraries and phage particles.
1 . A method of selecting cyclic peptides that bind to a desired target, said method comprising:
(a) transforming a phage display library comprising a plurality of nucleic acids into bacterial host cells,
wherein the nucleic acids comprise phage coat protein genes comprising a combinatorial region, and
wherein the combinatorial region encodes at least one cysteine and at least one non-canonical amino acid;
(b) expressing the phage coat protein genes within the bacterial host cells,
wherein the bacterial host cells produce phage particles from the nucleic acids,
wherein the phage particles contain phage coat proteins with the at least one cysteine and the at least one non-canonical amino acid in the combinatorial region, and
wherein the at least one cysteine and the at least one non-canonical amino acid couple to one another to form a cyclic peptide;
(c) screening the phage particles against the desired target,
wherein the screening results in the selection of phage particles with cyclic peptides that bind to the desired target; and
(d) identifying the amino acid sequences of the cyclic peptides of the selected phage particles.
2 . The method of claim 1 , wherein the screening occurs by:
(a) incubating the phage particles with the desired target,
wherein the desired target is immobilized on a surface;
(b) separating unbound phage particles from phage particles that are bound to the desired target; and
(c) isolating the bound phage particles; and
wherein the identifying comprises:
(a) purifying the selected phage particles;
(b) isolating the nucleic acids from the selected phage particles; and
(c) sequencing the combinatorial regions of the nucleic acids.
3 . The method of claim 1 , wherein the screening further comprises:
(a) transforming the selected phage particles into the bacterial host cells to allow for the production of additional phage particles; and
(b) re-screening the phage particles in accordance with step (b) of claim 1 , wherein the further screening is repeated multiple times.
4 . The method of claim 1 ,
wherein the desired target is selected from the group consisting of peptides, proteins, enzymes, enzymes inhibited by the cyclic peptides, proteases, histone deacetylases, TEV protease, HDAC8, small molecules, cell receptors, antigens, ligand binding sites of a desired target, active sites of a desired target, active sites of a protein, allosteric sites of a protein, DNA, RNA, and combinations thereof,
wherein the nucleic acids are in the form of phagemids, or wherein the nucleic acids are encapsulated in a phage,
wherein the bacterial host cells are capable of translating the combinatorial region of the phage coat protein gene such that the at least one cysteine and the at least one non-canonical amino acid are translated, and
wherein the bacterial host cells are co-infected with a knockout helper phage that does not express the phage coat protein gene.
5 . The method of claim 1 ,
wherein the at least one non-canonical amino acid is encoded by a codon selected from the group consisting of an in-frame amber codon, an in-frame ochre codon, an in-frame opal codon, a rare codon, and a four base codon,
wherein the at least one non-canonical amino acid is encoded by an in-frame amber codon,
wherein the bacterial host cells are an amber-suppressing bacterial host strain,
wherein the bacterial host cells contain an amber suppressor tRNA that has been aminoacylated with the at least one non-canonical amino acid by a cognate aminoacyl-tRNA synthetase, and
wherein the at least one non-canonical amino acid is selected from the group consisting of phenylalanine-derived non-canonical amino acids, lysine-derived non-canonical amino acids, non-canonical amino acids comprising an electrophilic moiety that is capable of reacting with the sulfur group of the at least one cysteine, an alkene-containing non-canonical amino acid, an alkyne-containing non-canonical amino acid, an alkyl halide-containing non-canonical amino acid, N 6 -acryloyllysine (AcrK), and combinations thereof.
6 . The method of claim 1 ,
wherein the phage coat protein gene is the PIII gene, wherein the phage coat protein gene is positioned near an IPTG-inducible promoter, and wherein the phage coat protein is expressed by exposing the bacterial host cells to IPTG.
7 . The method of claim 1 , wherein the at least one non-canonical amino acid is at one end of the combinatorial region and the at least one cysteine is at the other end of the combinatorial region, wherein the at least one non-canonical amino acid and the at least one cysteine are separated by at least 4 amino acids, and wherein the at least one cysteine and the at least one non-canonical amino acid couple to one another by a Michael addition reaction or a nucleophilic substitution reaction between the at least one cysteine and an electrophilic region of the at least one non-canonical amino acid.