Non-canonical amino acids and programmable biomolecules

Non-canonical amino acids (ncAAs) are building blocks that go beyond the 20 amino acids found in nature. By incorporating ncAAs into peptides and proteins at precise positions, it becomes possible to create molecules with chemical properties that natural biology cannot produce. This has direct applications in drug discovery, enzyme engineering, and industrial manufacturing.

What are non-canonical amino acids?

Proteins are built from amino acids, linked by peptide bonds into chains. In nature, 20 amino acids are available, each with a unique side group that determines its chemical behaviour. The ribosome reads triplet codons in messenger RNA and assembles the corresponding chain. The structure and function of the resulting protein depend on two things: the chemical composition of its amino acids and their position in the chain.

Non-canonical amino acids are any amino acids beyond that standard set of 20. They include molecules with reactive handles for bioconjugation, fluorescent groups for imaging, stabilising modifications for drug half-life, and side chains with no natural equivalent. Hundreds of ncAAs have been characterised, with the number growing as new chemistries are explored.

Why 20 amino acids are not enough

The drugs, enzymes, and materials that modern industry needs increasingly require chemical properties that the standard amino acid palette cannot provide. Protease resistance, extended circulation time, site-specific conjugation, enhanced binding affinity, novel catalytic activity: these properties often depend on functional groups that simply do not appear in the 20 natural amino acids.

Today's best-selling peptide drugs already rely on non-canonical amino acids. Semaglutide and tirzepatide (marketed as Ozempic, Wegovy, Zepbound, and Mounjaro) use ncAA modifications for degradation resistance and extended half-life. Industry analysts project that by 2030, several of the top-selling drugs globally will contain at least one ncAA.

How ncAAs create programmable biomolecules

The ribosome follows the instructions encoded in DNA. By engineering the genetic code and the translational machinery, it is possible to direct the ribosome to place new building blocks at exact positions in a protein chain with 100% sequence fidelity. The molecule is defined by its gene.

This is fundamentally different from chemical synthesis. In solid-phase peptide synthesis (SPPS), each residue is added step by step, with cumulative losses and side reactions. In ribosomal synthesis, the DNA sequence encodes the position of every monomer, natural or non-canonical.

Why DNA-encoded positioning matters

When the position of every amino acid, including non-canonical ones, is encoded in DNA, three things follow. First, every copy of the molecule is identical: there is no batch-to-batch variation in where the ncAA appears. Second, the molecule can be produced by fermentation rather than chemical synthesis, with all the scalability and sustainability advantages that implies. Third, the design can be iterated genetically, by changing the DNA sequence rather than redesigning a synthesis route.

Four classes of programmable biomolecule

Peptides: short chains with ncAAs at defined positions, for drugs and biopesticides. ncAAs enable protease resistance, membrane permeability, and receptor selectivity that natural peptides cannot achieve.

Proteins: longer chains forming complex three-dimensional structures. ncAAs enable site-specific bioconjugation handles for antibody-drug conjugates (ADCs), producing more homogeneous and potent therapeutics than conventional random conjugation methods.

Macrocycles: cyclic chains with constrained geometry, including depsipeptides. Cyclisation combined with ncAAs creates compact, stable molecules with strong target binding, relevant to intracellular drug targets that are currently considered undruggable.

Non-protein polymers: custom-designed biomolecules for materials applications including bioplastics and functional coatings. The ribosome becomes a programmable polymerisation machine for monomers that go well beyond amino acids.

How ncAAs will transform healthcare

In peptide therapeutics, ncAAs enable the next generation of GLP-1 receptor agonists, antimicrobial peptides, and interleukin mimetics with improved pharmacokinetic profiles.

In antibody-drug conjugates, precise ncAA placement replaces random lysine or cysteine conjugation, yielding ADCs with defined drug-to-antibody ratios and improved therapeutic windows.

In enzyme engineering, ncAAs introduce catalytic functional groups that expand the reaction space accessible to biological catalysts, enabling enantioselective transformations and novel chemistries.

Industrial applications beyond therapeutics

The same platform applies to crop protection peptides, nutritional proteins, cosmetic ingredients, and performance materials. Any application that benefits from precise molecular design and scalable biological production is a candidate for ncAA-enhanced biomolecules.

Frequently asked questions

Are ncAAs the same as unnatural amino acids? The terms overlap but are not identical. "Non-canonical amino acid" refers to any amino acid not in the standard set of 20 encoded by the universal genetic code. Some ncAAs occur in nature (such as selenocysteine), while others are entirely synthetic. "Unnatural amino acid" typically refers to the synthetic subset. In practice, the two terms are often used interchangeably in the literature.

How are ncAAs incorporated into proteins? There are two main routes. Chemical synthesis (such as SPPS) can place ncAAs at any position, but is limited in chain length and scale. Genetic code expansion uses engineered translation machinery to incorporate ncAAs ribosomally, with the position encoded in DNA. The ribosomal route enables fermentation-scale production with complete sequence fidelity.

Why are ncAAs useful in drug discovery? Many desirable drug properties, such as protease resistance, membrane permeability, extended half-life, and site-specific conjugation, depend on chemical groups that the 20 natural amino acids do not provide. ncAAs fill those gaps, enabling molecules with improved pharmacological profiles.

Can ncAAs be manufactured by fermentation? Yes, when incorporated via genetic code expansion. The engineered organism produces the ncAA-containing molecule during normal growth, using the same fermentation infrastructure as conventional biologics. This avoids the high waste and cost of chemical peptide synthesis.