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Abstract CRISPR-based DNA adenine base editors (ABEs) hold remarkable promises to address human genetic diseases caused by point mutations. ABEs were developed by combining CRISPR-Cas9 with a transfer RNA (tRNA) adenosine deaminase enzyme and through directed evolution, conferring the ability to deaminate DNA. However, the molecular mechanisms driving the efficient DNA deamination in the evolved ABEs remain unresolved. Here, extensive molecular simulations and biochemical experiments reveal the biophysical basis behind the astonishing base editing efficiency of ABE8e, the most efficient ABE to date. We demonstrate that the ABE8e’s DNA deaminase domain, TadA8e, forms remarkably stable dimers compared to its tRNA-deaminating progenitor and that the strength of TadA dimerization is crucial for DNA deamination. The TadA8e dimer forms robust interactions involving its R98 and R129 residues, the RuvC domain of Cas9 and the DNA. These locking interactions are exclusive to ABE8e, distinguishing it from its predecessor, ABE7.10, and are indispensable to boost DNA deamination. Additionally, we identify three critical residues that drive the evolution of ABE8e toward improved base editing by balancing the enzyme’s activity and stability, reinforcing the TadA8e dimer and improving the ABE8e’s functionality. These insights offer new directions to engineer superior ABEs, advancing the design of safer precision genome editing tools.
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Targeted exon skipping with AAV-mediated split adenine base editors
Abstract Techniques for exclusion of exons from mature transcripts have been applied as gene therapies for treating many different diseases. Since exon skipping has been traditionally accomplished using technologies that have a transient effect, it is particularly important to develop new techniques that enable permanent exon skipping. We have recently shown that this can be accomplished using cytidine base editors for permanently disabling the splice acceptor of target exons. We now demonstrate the application of CRISPR-Cas9 adenine deaminase base editors to disrupt the conserved adenine within splice acceptor sites for programmable exon skipping. We also demonstrate that by altering the amino acid sequence of the linker between the adenosine deaminase domain and the Cas9-nickase or by coupling the adenine base editor with a uracil glycosylase inhibitor, the DNA editing efficiency and exon-skipping rates improve significantly. Finally, we developed a split base editor architecture compatible with adeno-associated viral packaging. Collectively, these results represent significant progress toward permanent in vivo exon skipping through base editing and, ultimately, a new modality of gene therapy for the treatment of genetic diseases.
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- Award ID(s):
- 1430124
- PAR ID:
- 10150365
- Publisher / Repository:
- Nature Publishing Group
- Date Published:
- Journal Name:
- Cell Discovery
- Volume:
- 5
- Issue:
- 1
- ISSN:
- 2056-5968
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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