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Visualization of a multi-turnover Cas9 after product release
Biorxiv : the Preprint Server for Biology
|December 9, 2024
Summary
Truncating guide RNAs in CRISPR-Cas9 gene editing significantly speeds up enzyme turnover. This allows visualization of previously uncharacterized Cas9 states, revealing how DNA binding inhibits re-binding and explaining its single-turnover kinetics.
Area of Science:
- Molecular Biology
- Biochemistry
- Structural Biology
Background:
- The CRISPR-Cas9 system is a powerful gene editing tool.
- Streptococcus pyogenes Cas9 (SpCas9) exhibits slow turnover, hindering DNA repair and limiting editing efficiency.
- Understanding Cas9 dissociation mechanisms is crucial for improving gene editing.
Purpose of the Study:
- To investigate the mechanisms underlying Cas9 dissociation from DNA.
- To engineer Cas9 for faster turnover and improved gene editing efficiency.
- To capture and characterize transient Cas9-DNA complex states.
Main Methods:
- Utilized truncated guide RNAs to weaken PAM-distal interactions.
- Employed kinetics-guided cryo-electron microscopy (cryo-EM) to capture transient states.
- Analyzed the conformational landscape of Cas9 during dissociation.
Main Results:
- Guide RNA truncation accelerated Cas9 turnover significantly.
- Identified previously uncharacterized Cas9 reaction states, including dissociation intermediates.
- Observed rapid dissociation of the PAM-distal product but tight binding of the PAM-proximal product.
Conclusions:
- Tight binding of the PAM-proximal product inhibits new target binding, explaining Cas9's single-turnover kinetics.
- Guide RNA truncation is a viable strategy to enhance Cas9 turnover.
- Findings provide insights for engineering improved Cas9 variants for gene editing.
