McrA Variants for Selective Methylated DNA Binding
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Solution Overview
Problem
Current methods for analyzing DNA methylation patterns are time-consuming, require large DNA samples, and struggle with precise identification of methylation sites, often leading to false positives due to incomplete digestion or lack of cleavage by restriction enzymes, and bisulfite-based methods limit analysis to a single PCR amplicon or a moderate number of amplicons.
Innovation Solution
Development of McrA protein variants with altered amino acid sequences or chemical modifications that maintain binding activity while selectively cleaving or not cleaving DNA with methylated cytosine, allowing for the separation and identification of methylated DNA without prior knowledge of sequence or fragment sizes, using immobilized variants and reporter tags for visualization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If restriction digestion is used to analyze DNA methylation patterns, then methylation sites can be identified through cleavage patterns, but the method is time-consuming and requires large amounts of DNA
Solution Approach 1:
The invention extracts and utilizes the specific property of McrA protein that recognizes and binds to methylated DNA sequences. By employing McrA variants with altered amino acid sequences, the method selectively binds to methylated cytosine sites without requiring complete digestion, thereby extracting the essential information needed for methylation analysis while avoiding the time-consuming nature of complete restriction digestion
Solution Approach 2:
The invention changes the parameters of the McrA protein by introducing amino acid substitutions (such as E256Q, E256A, E256D, E256N, E256K, E256R, E256M, E256L, E256I, E256V, E256F, E256S, E256T, E256P, E256G, E256H, E256Y, E256W, E256C, E256Q, E256X) that modify its catalytic activity while preserving or enhancing its binding affinity for methylated DNA. This allows the protein to function as a binding agent rather than a cleaving enzyme, enabling detection without complete digestion
2Measurement precision
If restriction enzymes are used for DNA methylation analysis, then cleavage patterns indicate methylation status, but incomplete digestion leads to false positive results
Solution Approach 1:
Instead of using restriction enzymes that cleave DNA and requiring complete digestion to avoid false positives, the invention inverts the approach by using McrA variants that bind to methylated DNA without cleaving it. This inversion transforms the detection mechanism from a cleavage-based method (where incomplete digestion causes false positives) to a binding-based method (where bound DNA can be directly detected), thereby eliminating the false positive problem
Solution Approach 2:
The invention introduces an intermediary detection system where McrA variants bind to methylated DNA and are subsequently detected through their binding activity. This intermediary binding step serves as a reliable indicator of methylation status, eliminating the need to rely on complete enzymatic digestion and thereby preventing false positive results
3Measurement precision
If bisulfite conversion is used to identify methylation sites, then precise identification is achieved, but analysis is limited to a single or moderate number of amplicons
Solution Approach 1:
The invention creates McrA variants with universal binding capability that can recognize and bind to methylated cytosine sites across diverse DNA sequences and locations. The variants maintain their ability to bind methylated DNA while exhibiting altered catalytic activity, enabling them to function as universal binding agents for methylation detection. This universality allows simultaneous analysis of multiple noncontiguous methylation sites throughout the genome, overcoming the limitation of bisulfite conversion which is restricted to single or moderate numbers of amplicons
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
Enables efficient separation and identification of methylated DNA, reducing false positives and allowing for analysis of multiple noncontiguous methylation sites simultaneously, with variants capable of distinguishing between methylated and hydroxymethylated substrates, thus improving epigenetic mapping and cancer research.
Implementation Method 1
The McrA protein has been shown to bind specifically to sequences containing methylated cytosine
Implementation Method 2
McrA is a sequence-specific endonuclease that cleaves DNA containing methylated cytosine
Implementation Method 3
Treatment of DNA with sodium bisulfite converts unmethylated, but not methylated, cytosine to uracil
Data Source
AI summary
Compositions and methods are provided in which the composition is a protein with at least 50% but less than 100% amino acid sequence identity with McrA or is a variant McrA protein with at least one amino acid sequence modification. The variant or protein has the property of cleaving DNA with methylated cytosine and not hydroxymethylated cytosine in a target DNA sequence, or substantially lacks catalytic activity while maintaining binding activity. Methods are provided in which the protein or McrA variant are used to identify methylation sites either by cleavage or by binding to the methylation site in the presence of a marker or by binding to an immobilized protein or McrA variant.