Expanding the genetic code with diverse backbone structures across diverse sequence contexts

Abstract Expanding the genetic code to enable the selective and specific incorporation of non-canonical monomers (ncMs), beyond α-L amino acids with variant sidechains, is a key outstanding challenge. Here we discover orthogonal aminoacyl-tRNA synthetases that selectively and specifically acylate their cognate orthogonal tRNA in vivo with eleven new ncMs spanning five different chemical classes: α,α-disubstituted-amino acids, malonic acids, carboxylic acids, β 2 -amino acids and N-cyclic amino acids. We demonstrate that co-translational incorporation of α,α-disubstituted-amino acids, β 2 -amino acids, β 3 -amino acids and N-cyclic amino acids is strongly dependent on the codons either side of the codon used to direct ncM incorporation, with several ncMs incorporated at less than 1% of sequence contexts. We evolve orthogonal tRNAs that enable the incorporation of previously unincorporated ncMs, enable the incorporation of ncMs at >95% of sequence contexts and, increase the incorporation efficiency at challenging sequence contexts up to 40-fold. We demonstrate the encoded cellular synthesis of proteins and macrocycles containing ncMs and, explicitly demonstrate that our evolved tRNAs provide direct access to a wider range of genetically encoded macrocyclic sequences containing ncMs. Our results provide a foundation for composing, discovering and manufacturing proteins and peptides with functions augmented by ncMs.