Adenine Base Editor P48R Mutation for Cytosine Editing Specificity
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Solution Overview
Problem
Adenine base editors suffer from off-target effects due to incomplete target specificity and DNA/RNA-binding properties, while cytosine base editors have a wide operating range and inappropriate base substitution issues, limiting their precision in gene editing.
Innovation Solution
An adenine base editor with a P48R mutation in adenosine deaminase and CRISPR-associated protein 9 (Cas9) fusion, optionally linked with uracil-DNA glycosylases, is developed to enhance thymine-cytosine sequence-specific cytosine base editing activity, allowing precise substitution of cytosine with thymine or guanine based on the presence of uracil-DNA glycosylases.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If adenine base editors are used for gene editing, then A/T pair conversion efficiency is improved, but off-target effects increase due to incomplete target specificity and DNA/RNA-binding properties
Solution Approach 1:
The patent introduces specific mutations (P48R, V106W, E59A) in the adenosine deaminase component of the base editor to change its biochemical parameters. These mutations reduce the enzyme's affinity for RNA and non-specific DNA binding, thereby reducing off-target effects while preserving on-target editing efficiency
Solution Approach 2:
The patent applies different mutations to different regions of the adenosine deaminase protein to achieve localized functional modifications. The P48R mutation addresses RNA binding specificity, V106W addresses off-target DNA binding, and E59A addresses overall specificity, allowing precise control over different aspects of the enzyme's behavior
2Adaptability or versatility
If cytosine base editors are used for gene editing, then cytosine substitution capability is improved, but operating range becomes too wide causing undesired base editing
Solution Approach 1:
The patent narrows the operating range of the base editor by introducing mutations that restrict the enzyme's activity to specific sequence contexts. The P48R mutation in particular creates stricter sequence requirements, ensuring that editing occurs only at desired TC sites rather than across a broad range of positions
Solution Approach 2:
The patent uses the P48R mutation to create a more restrictive enzyme that performs editing action only under specific conditions (TC sequence context), rather than allowing excessive action across all possible cytosine positions. This partial action approach ensures precision by limiting activity to only the most appropriate target sites
3Productivity
If cytosine base editors are used for gene editing, then cytosine substitution is achieved, but inappropriate base substitution occurs with bases other than thymine
Solution Approach 1:
The patent modifies the enzymatic parameters of the base editor through mutations that enhance specificity for thymine incorporation. The V106W mutation in particular alters the enzyme's substrate preference and catalytic properties to favor thymine substitution over other bases, thereby improving substitution specificity while maintaining editing productivity
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 adenine base editor achieves sophisticated cytosine base editing with high specificity, enabling precise editing of cytosine to thymine or guanine, improving upon conventional base editors by reducing off-target effects and enhancing editing precision across various organisms, including humans, plants, and bacteria.
Implementation Method 1
adenosine deaminase (wild-type tRNA-specific adenosine deaminase, which is TadA from Escherichia coli (wtTadA), and modified TadA (eTadA), which is TadA7.10 evolved to operate on DNA instead of RNA)
Data Source
AI summary
Proposed are an adenine base editor having increased thymine-cytosine sequence-specific cytosine base editing activity, a cytosine base editing method, and a cytosine base editing kit. The editor, produced by introducing a P48R mutation into an adenosine deaminase, has an operating range that is more sophisticated than conventional cytosine base editors, allows cytosine base editing only when cytosine is positioned right behind thymine, thereby enabling elaborate editing even when there is a plurality of cytosines within the range, and enables cytosine to be substituted with thymine or guanine in the presence or absence of UGI, respectively. Therefore, the cytosine base editing composition can be effectively used in the fields of gene therapy or new crop development which requires precise editing of only cytosine in all living organisms, including humans, plants, and bacteria.