Non-enzymatic Oxidation of Modified Cytosine Residues
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Solution Overview
Problem
Current methods for detecting 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) in nucleic acids face challenges such as sequence-specific biases, degradation of polynucleotides, and inability to distinguish between these residues and canonical cytosine, leading to reduced accuracy in sequencing and genetic variant detection.
Innovation Solution
A non-enzymatic method involving a one-electron oxidation process using a radical initiator, such as a photocatalyst, to convert 5mC and 5hmC into 5-formylcytosine (5fC), which can be labelled and detected, allowing for selective identification of these residues within polynucleotides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If TET enzymes are used to oxidise 5mC to 5caC, then detection of 5mC is enabled, but sequence-specific biases occur and polynucleotide degradation increases
Solution Approach 1:
The patent replaces the enzymatic oxidation system (TET enzymes) with a chemical oxidation system using iron(II) and hydrogen peroxide to generate hydroxyl radicals. This substitution eliminates sequence-specific biases inherent in enzymatic recognition while maintaining the oxidation function needed to convert 5mC to 5caC for detection.
Solution Approach 2:
The patent changes the oxidation mechanism from enzyme-catalyzed to chemically-generated radical-mediated oxidation. By using Fenton chemistry (iron(II) + hydrogen peroxide → hydroxyl radicals), the system achieves oxidation without the sequence-specific constraints of enzymatic recognition, thereby improving reliability across different sequence contexts.
2Measurement precision
If bisulfite conversion is used to detect 5mC, then C to T change is effected for sequencing, but DNA cleavage occurs causing loss of sequenceable material
Solution Approach 1:
The patent performs oxidation of 5mC to 5caC before sequencing, converting the modified base into a form that can be distinguished from canonical cytosine during sequencing. This preliminary chemical modification enables accurate detection without requiring subsequent bisulfite treatment that would cause DNA cleavage and material loss.
3Ease of operation
If all C residues are converted to T in sequencing, then 5mC detection is simplified, but C-to-T genetic variants cannot be detected
Solution Approach 1:
The patent uses 5caC as an intermediary form that preserves the original cytosine identity information. By oxidizing 5mC to 5caC (which has distinct chemical properties from both 5mC and canonical C), the method enables differentiation between methylated and unmethylated cytosines while retaining the ability to detect C-to-T genetic variants through appropriate sequencing and analysis.
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
This method enables accurate and efficient detection of 5mC and 5hmC with minimal polynucleotide degradation, providing a higher yield of 5fC and reducing sequence-specific biases, thus enhancing the accuracy of sequencing and genetic variant analysis.
Implementation Method 1
A non-enzymatic method involving a one-electron oxidation process using a radical initiator, such as a photocatalyst, to convert 5mC and 5hmC into 5-formylcytosine (5fC)
Data Source
AI summary
The invention provides a method for identifying a modified cytosine residue, which may be 5-methylcytosine or 5-hydroxymethylcytosine, in a nucleotide sequence. The method comprises oxidising the modified cytosine residue through a non-enzymatic, one-electron process to form 5-formylcytosine. The presence of 5-formylcytosine can be established by labelling and identifying this residue. The invention also provides a method of modifying a polynucleotide containing a 5-methylcytosine and/or a 5-hydroxymethylcytosine residue, a method of oxidising 5-methylcytosine, 5-hydroxymethylcytosine, a 5-methylcytosine residue, or a 5-hydroxymethylcytosine residue, use of a non-enzymatic radical initiator to oxidise a 5-methylcytosine or 5-hydroxymethylcytosine residue, and a kit for use in the methods.