Description

In this technological feat, scientists built a system where E. coli produces and incorporates a new catalytic amino acid — S-(4-aminophenyl)-L-cysteine (pAPhC) — all inside the same cell. No external synthesis. No expensive feeding. Just pure biosynthetic wizardry.

The magic ingredient? A mercapto-aniline group — a catalytic handle never seen in nature — that turns ordinary proteins into true chemical machines. Using this approach, the team created a designer enzyme that performs an enantioselective Friedel–Crafts alkylation (a reaction beloved by organic chemists for building chiral carbon-carbon bonds in pharmaceuticals, agrochemicals and fragrances) with 95% enantiomeric excess and 98% yield. This merges metabolic engineering and genetic code expansion — effectively teaching cells to forge their own xenobiotic chemistry.

Citation: Huang et al., 2025

Complete biosynthesis means producing and incorporating a non-canonical amino acid entirely within the host cell, without external chemical synthesis or feeding. This removes a major bottleneck in ncAA production: the cost and complexity of synthesising and supplementing non-natural building blocks.

Researchers engineered E. coli to both synthesise S-(4-aminophenyl)-L-cysteine (pAPhC), a mercapto-aniline-containing ncAA, and incorporate it into proteins via genetic code expansion. The resulting designer enzyme catalysed enantioselective Friedel-Crafts alkylation with 95% enantiomeric excess and 98% yield. The catalytic chemistry performed by pAPhC does not exist anywhere in nature's amino acid toolkit (Huang et al., 2025).

This convergence of metabolic engineering and genetic code expansion points toward a future where recoded organisms produce their own non-canonical building blocks at fermentation scale. For Constructive Bio's platform, complete biosynthesis is the logical endpoint: cells that manufacture both the ncAA and the therapeutic molecule in a single fermentation run.

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