S. aureus KKH-ABE8e Adenine Base Editor
Expanded-PAM variant of SaABE8e with KKH mutations (E782K/N968K/R1015H) enabling NNNRRT PAM recognition.
Origin: TadA8e deaminase fused to S. aureus Cas9-KKH D10A nickase with expanded PAM specificity
Characteristics
KKH mutations (E782K/N968K/R1015H) expand PAM from NNGRRT to NNNRRT, increasing targetable sites. Maintains single-AAV compatibility. Achieved highest therapeutic editing in vivo with 93% knockdown of PCSK9/Pcsk9/Angptl3 and substantial reductions in plasma cholesterol and triglycerides. Demonstrates superior on-target activity compared to NNGRRT PAM variant.
Applications
Single-AAV adenine base editing with expanded targeting scope for cardiovascular and metabolic diseases. Validated for lipid-lowering therapy via PCSK9 and ANGPTL3 editing. Preferred variant when target sites contain NNNRRT but not NNGRRT PAMs. Suitable for hard-to-transduce tissues requiring high editing efficiency.
Limitations
NNNRRT PAM still more restrictive than SpCas9 NGG. Approaches single-AAV packaging limits (~4.5 kb). Potential for increased off-target editing due to relaxed PAM specificity, though guide-dependent off-targets remain dose-dependent and manageable.
Literature References
- Gaudelli NM, Komor AC, Rees HA, et al. (2017). Programmable base editing of A•T to G•C in genomic DNA without DNA cleavage. Nature 551:464-471 - Gaudelli 2017 Adenine Base Editor
- Richter et al. (2020). Phage-assisted evolution of an adenine base editor with improved Cas domain compatibility and activity. Nat Biotechnol - Richter 2020 ABE8e
- Davis et al. (2022). Efficient in vivo base editing via single adeno-associated viruses with size-optimized genomes encoding compact adenine base editors. Nat Biomed Eng - Davis 2022 Single-AAV ABEs