Engineered Cas9 Nuclease Specificity via Residue Mutations
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Solution Overview
Problem
CRISPR-Cas9 nucleases face challenges in specificity, often inducing off-target mutations at imperfectly matched target sites due to non-specific interactions with DNA, which can lead to unintended genomic alterations.
Innovation Solution
Engineering Cas9 variants, such as SpCas9 and SaCas9, with specific mutations at residues that interact with the DNA backbone, like N497A, R661A, Q695A, and Q926A, to reduce non-specific binding affinity and enhance target specificity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If Cas9 binds strongly to DNA to ensure efficient on-target cleavage, then cleavage efficiency is improved, but off-target binding increases causing non-specific mutations
Solution Approach 1:
The patent applies parameter changes by systematically mutating specific amino acid residues (N497, R661, Q695, Q926) in the Cas9 protein to alter its DNA binding parameters. These mutations reduce the binding affinity at off-target sites while preserving sufficient affinity for on-target sites, thereby changing the binding characteristics to achieve both high efficiency and high specificity.
Solution Approach 2:
The patent applies local quality by making specific localized mutations at four key positions (N497A, R661A, Q695A, Q926A) within the Cas9 protein structure. These localized changes affect the DNA interaction interface specifically, allowing the protein to maintain overall function while improving discrimination between target and off-target sites through altered local chemical properties.
2Manufacturing precision
If mutations are introduced to reduce non-specific binding, then target specificity is improved, but binding affinity may decrease affecting on-target activity
Solution Approach 1:
The patent optimizes binding parameters by selecting specific amino acid substitutions that differentially affect on-target versus off-target binding. The mutations at N497, R661, Q695, and Q926 are chosen to reduce affinity for mismatched sequences while maintaining affinity for perfectly matched target sequences, thus changing binding parameters to achieve both high specificity and preserved on-target activity.
Solution Approach 2:
The patent employs feedback through systematic evaluation of mutant Cas9 variants to identify combinations that achieve the desired balance. By testing and selecting specific mutation combinations (N497A, R661A, Q695A, Q926A), the invention uses feedback from experimental data to optimize the balance between specificity and activity, ensuring that on-target function is preserved while off-target effects are reduced.
Data Source
Figure 1A
Figure 1B~1C
Figure 1D~1E
AI summary
Engineered CRISPR-Cas9 nucleases with improved specificity and their use in genomic engineering, epigenomic engineering, genome targeting, and genome editing.