Secondary Conformational Checkpoint in CRISPR-Cas9.

Area of Science:

• Molecular Biology
• Biochemistry
• Genetics

Background:

• CRISPR-Cas9 gene editing precision is crucial but not fully understood at the molecular level.
• Existing CRISPR-Cas9 variants aim to improve DNA cleavage accuracy, yet their mechanisms require deeper investigation.

Purpose of the Study:

• To investigate the late-stage conformational dynamics of Cas9 and an evolved variant (evoCas9) in the precleavage state.
• To elucidate the molecular mechanisms underlying the enhanced accuracy of evoCas9.

Main Methods:

• Sub-millisecond dynamic simulations were employed to observe conformational transitions.
• Analysis focused on the HNH nuclease domain's motion and allosteric communication networks.

Main Results:

• Base mismatches disrupt Cas9's HNH nuclease domain motion, impairing conformational activation and suggesting a secondary checkpoint.
• evoCas9 exhibits altered activation pathways with mismatches, including HNH domain repositioning and perturbed allosteric networks.
• Mutations in evoCas9 reinforce both primary and secondary checkpoints, ensuring high gene-editing accuracy.

Conclusions:

• A secondary conformational checkpoint fine-tunes Cas9 DNA cleavage activation, particularly in the presence of base mismatches.
• The evolved Cas9 variant (evoCas9) utilizes enhanced checkpoint mechanisms for superior gene-editing fidelity.
• The identified mechanism likely applies to other high-fidelity Cas9-guide RNA variants.