AI just designed molecular scissors from scratch ✂️
Most medicines work by holding on. A drug or an antibody binds its target and blocks it, one molecule at a time, so a million copies of a disease protein need roughly a million copies of the drug. Enzymes play a different game: they change their target, let go, and move on to the next one. Last week, the Baker lab at the University of Washington's Institute for Protein Design published two papers in Nature showing that AI-driven design can now build enzymes that cut proteins at a spot you choose. That has been a long-standing open problem, and I find it genuinely exciting.
Why cutting proteins is so hard
The bonds that hold amino acids together are extremely stable: in neutral water a peptide bond can last for hundreds of years. Natural proteases get around that with a "blade" positioned with near-atomic precision, plus a subtle flexibility to grip the right sequence. Getting both right in a protein designed from nothing has been out of reach for a long time.
The teams used deep-learning design tools: a version of RFdiffusion to build the backbones, ProteinMPNN to pick sequences, and AlphaFold 3 to filter the candidates before anything went into the lab.
Two kinds of scissors
Cysteine proteases (led by Hojae Choi) use an activated cysteine as the blade. 13 of 69 designs worked (19%), with rate enhancements of up to 3 × 107 over the uncatalysed reaction. Their folds look nothing like natural proteases, yet six crystal structures matched the design models to within 1.2 Å. And they cut their targets inside living human cells.
Metalloproteases (led by Anqi Chen and Kejia Wu) use a zinc ion instead. Of 135 designs, 36% cut their target peptide at the intended bond. The best one speeds up the reaction more than 100-million-fold, and four mutations push that past 1010. The team then designed proteases that selectively cut disease-related proteins: TDP-43 (linked to ALS and frontotemporal dementia), amyloid-β (Alzheimer's) and serum amyloid A, with rate enhancements of up to 109. They also built "caged" signalling proteins that only switch on when the matching designed protease cuts them free.
Why this is beautiful
What I love here is the shift from AI that predicts protein shapes to AI that designs proteins that do chemistry. David Baker put it as moving to "designing machinery that physically changes matter at the atomic level." Because one enzyme can cut thousands to millions of targets over its lifetime, this could eventually mean lower doses, and a way to reach proteins that offer no pocket for a classic drug.
To keep it honest: this is lab work, not a treatment. The disease targets were tested as peptides or purified proteins (including full-length TDP-43 in a test tube), and the authors note their designs are still less active than the best natural cysteine proteases. But the code is open, the structures are in the Protein Data Bank, and the success rates are high enough that other labs can build on this right away.
Programmable scissors for proteins, designed with AI: that's a sentence I wouldn't have believed a few years ago. 🧬
Sources
- UW Medicine news release: Molecular 'scissors' open path to new therapies
- Nature: Computational design of metalloproteases
- Nature: De novo design of cysteine proteases
- Code: cysteine protease design pipeline on GitHub
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