Cas9 Variants with Enhanced Specificity via Seed Mutations
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Solution Overview
Problem
Current CRISPR-Cas9 systems face challenges in specificity, leading to off-target cleavage issues, which affect the accuracy of genome editing and engineering applications.
Innovation Solution
Development of Streptococcus pyogenes Cas9 (SpCas9) protein variants with specific mutations, such as R63A and Q768A, along with additional mutations like D10A, H840A, H840N, or N840Y, to enhance specificity and reduce nuclease activity, combined with nuclear localization signals and tags for improved performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Cas9 uses a longer seed sequence requirement for full complementarity, then specificity is improved and off-target cleavage is reduced, but the ability to efficiently cleave target DNA may be compromised
Solution Approach 1:
The patent applies parameter changes by modifying specific amino acid residues (R63A, Q768A, and combinations with D10A, H840A, H840N, or N840Y) in the Cas9 protein sequence to alter its interaction with the seed sequence. These mutations change the protein's specificity parameters to require longer or more stringent seed sequence complementarity, thereby reducing off-target cleavage while maintaining efficient on-target activity through optimized binding kinetics.
2Reliability
If Cas9 is engineered with mutations to enhance specificity, then off-target effects are reduced, but the complexity of the protein sequence increases
Solution Approach 1:
The patent applies local quality by introducing mutations at specific localized positions (R63 and Q768) within the Cas9 protein rather than altering the entire sequence. These targeted local changes at critical residues in the seed sequence binding region achieve enhanced specificity without requiring complex global sequence modifications, thus maintaining protein simplicity while improving reliability.
3Measurement precision
If additional mutations like D10A, H840A, H840N, or N840Y are introduced to reduce nuclease activity, then specificity is improved, but the overall protein function may be attenuated
Solution Approach 1:
The patent applies dynamics by creating a balanced set of mutations where some residues (R63A, Q768A) primarily enhance specificity while others (D10A, H840A, H840N, N840Y) modulate nuclease activity. The combination of these mutations creates a dynamic equilibrium where the protein maintains sufficient catalytic power for efficient on-target cleavage while exhibiting heightened sensitivity to mismatches in the seed sequence, thereby achieving both high specificity and retained function.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The modified SpCas9 variants demonstrate significantly enhanced specificity, reducing off-target effects and improving the precision of genome editing, particularly in eukaryotic cells, for applications in treating genetic disorders and genome engineering.
Implementation Method 1
Sufficient base pairing between the crRNA and target DNA leads to the formation of a stable R-loop
Implementation Method 2
This induces subsequent cleavage of the target and non-target strand by the HNH and RuvC endonuclease domains of Cas9, respectively, which results in a double-strand break
Data Source
AI summary
The present invention relates to engineered Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR)/CRISPR-associated protein 9 (Cas9) variants with enhanced specificity compared to wild type Cas9. The present invention also relates to compositions comprising one or more of those Cas9 variant(s), wherein the composition can be used for genome engineering. Furthermore, the present invention relates to pharmaceutical compositions comprising one or more of those Cas9 variant(s), wherein the pharmaceutical compositions can be used for treating disease(s), such as genetic disorders.