AI-guided redesign of laboratory-evolved reverse transcriptases enhances prime editing
@NatureBiotech
1. The study identifies a key bottleneck in state-of-the-art prime editors: reverse transcriptases (RTs) optimized by directed evolution often trade catalytic gains for poorer folding, reduced stability, and lower intracellular expression—limiting performance especially in transient delivery settings.
2. To address this, the authors apply structure-informed AI redesign (ProteinMPNN) to RT domains from multiple prime editor lineages (PEmax, PE6a, PE6c, PE6d), while explicitly preserving residues near substrates and highly conserved positions to protect catalytic function.
3. The redesign strategy is unusually aggressive: redesigned RTs carry 30–163 amino acid substitutions (up to ~24% sequence divergence; up to ~40% of residues allowed to vary in candidate designs), far beyond prior prime editor engineering efforts that typically introduced ≤17 RT substitutions.
4. A practical pipeline is demonstrated: AlphaFold-predicted structures guide ProteinMPNN sequence generation under distance-to-substrate and conservation constraints, followed by AlphaFold2 filtering using pLDDT and RMSD to retain structurally faithful designs before synthesis and screening.
5. In an mRNA-LNP screen (Pcsk9 1 TTAC in Hepa1-6 cells), 95% of redesigned RTs remained functional (>5% editing), and ~30% outperformed their parental editors—showing that broad sequence exploration can still preserve complex RT-dependent prime editing activity.
6. Broad validation uses a pooled “self-targeting” lentiviral assay covering 700 ClinVar pathogenic variants (plus controls), totaling 16,800 prime-edit measurements across redesigned RTs; top redesigned variants improve average editing efficiency across many edits, particularly for heavily evolved RTs.
7. The best redesigned editors are named PE8 variants: PE8a (from PE6a), PE8c (from PE6c), PE8d (from PE6d), and PE8max (from PEmax). Across multiple comparisons, PE8 variants often exceed PE6/PEmax and also outperform PE7 (PEmax–La) in several tested contexts.
8. Mechanistically, redesigned RTs increase soluble expression and stability: intracellular prime editor protein levels after mRNA-LNP delivery rise up to ~2-fold (peak at ~8 h), bacterial soluble RT yields improve, and DSF shows notable thermostability gains for some designs (for example, PE8c RT 8 °C Tm over PE6c).
9. The work emphasizes that higher expression/stability translates into better editing under therapeutically relevant delivery constraints: improvements are shown in primary human fibroblasts, CD34 HSPCs, and primary T cells via mRNA electroporation, and via eVLP RNP delivery.
10. In vivo (mouse liver, Pcsk9 1 TTAC), PE8 variants increase editing up to 2.9-fold versus PE6/PEmax under modest dosing; higher in vivo protein expression accompanies higher editing, while edit:indel ratios and candidate off-target analyses remain comparable to prior editors.
💻Code:
github.com/Allentaoyz/Redesi…
📜Paper:
doi.org/10.1038/s41587-026-0…
#PrimeEditing #GenomeEditing #CRISPR #ProteinDesign #ProteinMPNN #AlphaFold #DirectedEvolution #mRNADelivery #LNP #ComputationalBiology