Genetic Code Expansion in Protein Engineering

Genetic code expansion harnesses engineered translation machinery to incorporate noncanonical amino acids into proteins at designated sites, thereby reprogramming the chemical language of living cells. By deploying orthogonal aminoacyl-tRNA synthetase/tRNA pairs and repurposing codons—most often the amber stop codon—researchers can introduce side chains bearing unique spectroscopic probes, reactive handles or functional groups absent from the canonical twenty amino acids. This approach has enabled new insights into enzyme mechanisms, the creation of bespoke biocatalysts with enhanced selectivity and stability, and the design of proteins responsive to chemical or optical stimuli. Advances in ribosome engineering and tRNA evolution have begun to overcome substrate scope limitations, permitting incorporation of β-amino acids, α,α-disubstituted residues and non-proteinogenic monomers. Applications span from super-resolution imaging of cytoskeletal structures and precise therapeutic conjugates to the assembly of artificial enzymes with expanded catalytic repertoires. As genetic code expansion methodologies mature, they promise to transform fields as diverse as structural biology, synthetic biology and therapeutic protein design by enabling site-specific installation of novel chemistries into living systems.

Research from Nature Portfolio

Recent studies have broken through long-standing barriers in monomer scope by developing selection platforms that decouple synthetase evolution from ribosomal compatibility. A newly devised tRNA display technique permits high-throughput screening of orthogonal synthetases that charge tRNAs with diverse noncanonical monomers—including β-amino acids and α,α-disubstituted residues—without requiring the monomers to be ribosomal substrates. This advance has enabled the first cellular incorporation of these monomers into proteins, expanding the genetic code beyond α-l-amino acids. In parallel, the design of two novel noncanonical amino acids bearing mutually orthogonal azide and tetrazine handles has facilitated one-pot, site-specific conjugation of proteins with fluorophores, radioisotopes, polymers and drugs. By encoding both handles into a single protein, researchers have produced homogeneous dual and even triple conjugates in living cells, opening new avenues for multimodal imaging and targeted therapeutic delivery.

Genetic Code Expansion in Protein Engineering publication trend

The graph below shows the total number of articles in genetic code expansion in protein engineering across all publications each year (not limited to Nature Index journals).

Technical terms

Noncanonical amino acid: An amino acid not among the standard twenty, introduced genetically to confer novel chemical functionality on proteins.

Orthogonal translation system: A deliberately engineered aminoacyl-tRNA synthetase and cognate tRNA pair that functions independently of the host’s endogenous translation machinery.

Amber suppression: A technique that repurposes the UAG stop codon to encode a noncanonical amino acid by using an orthogonal tRNA charged with that amino acid.

Bioorthogonal chemistry: Chemical reactions that proceed selectively and rapidly in living systems without interfering with native biochemical processes.

Codon reassignment: The systematic repurposing of a codon’s meaning from a canonical amino acid or stop signal to a noncanonical monomer via engineered translation components.

References

1. Noncanonical Amino Acids in Biocatalysis. Chemical Reviews (2024).
2. Adding α,α-disubstituted and β-linked monomers to the genetic code of an organism. Nature (2024).
3. Noncanonical amino acids as doubly bio-orthogonal handles for one-pot preparation of protein multiconjugates. Nature Communications (2023).
4. Designing logical codon reassignment – Expanding the chemistry in biology. Chemical Science (2015).
5. Genetic Code Expansion Enables Live-Cell and Super-Resolution Imaging of Site-Specifically Labeled Cellular Proteins. Journal of the American Chemical Society (2015).
6. Genetically Encoded Optochemical Probes for Simultaneous Fluorescence Reporting and Light Activation of Protein Function with Two-Photon Excitation. Journal of the American Chemical Society (2014).