APOBEC1 Base Editor Variants for Low Off-Target RNA Editing
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Solution Overview
Problem
Existing base editors induce unwanted mutations in both RNA and DNA, leading to off-target effects that are not effectively mitigated by current improvements in target specificity and deaminase mutants.
Innovation Solution
Development of APOBEC1 variants with specific mutations, such as F66L+V179I, I195N, and C82R, which reduce RNA editing activity while maintaining DNA editing capacity, integrated into a fusion protein with Cas9 for safer genomic editing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If APOBEC1 deaminase is used in base editors, then DNA editing activity is achieved, but off-target mutations in both DNA and RNA occur
Solution Approach 1:
The patent applies parameter changes by introducing specific amino acid mutations (F66L, V179I, I195N, C82R) in the APOBEC1 deaminase to alter its enzymatic parameters. These mutations modify the enzyme's substrate specificity and catalytic activity, reducing its ability to access and edit off-target sites while preserving on-target editing efficiency. This directly addresses the contradiction by changing the biochemical parameters of the deaminase to minimize harmful off-target effects.
Solution Approach 2:
The patent applies local quality by creating spatial differentiation in the deaminase's activity. The mutated APOBEC1 exhibits localized editing capability that is restricted to specific on-target sites guided by Cas9-gRNA complexes, while its activity is suppressed at potential off-target sites. This local quality control ensures that the deaminase's harmful effects are confined or eliminated while maintaining beneficial on-target function.
2Productivity
If deaminase activity is increased to improve editing efficiency, then DNA editing capacity is enhanced, but RNA editing activity and off-target effects increase
Solution Approach 1:
The patent applies parameter changes by mutating specific amino acid residues (F66L, V179I, I195N, C82R) to alter the deaminase's catalytic parameters. These mutations reduce the enzyme's affinity for RNA substrates while maintaining or enhancing its activity on DNA substrates at target sites. This selective parameter modification resolves the contradiction by decoupling DNA editing efficiency from harmful RNA editing activity.
Solution Approach 2:
The patent applies inversion by reversing the normal relationship between deaminase activity and specificity. Instead of using a highly active deaminase that edits both DNA and RNA, the patent uses a mutated deaminase where the activity is inverted or restricted to work primarily on DNA at specific Cas9-guided sites while being inhibited from editing RNA. This inverted approach maintains productivity while eliminating harmful side effects.
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 APOBEC1 variants significantly minimize off-target mutations in both RNA and DNA, enabling precise genomic editing with enhanced safety and reduced unintended alterations.
Implementation Method 1
a deaminase that induces modification of a specific base, used in genomic editing techniques... For cytosine to thymine mutation (C>T editing), the most commonly used deaminase is rat APOBEC1, a potent DNA mutator that acts physiologically on RNA
Data Source
AI summary
Nucleotide sequences coding for variants of the cytidine deaminase protein characterised by specific point mutations, and their use in the preparation of fusion proteins with Cas-9 for use in DNA editing techniques are described.