Exo-Exo DNA Polymerase Variants for Sequencing Accuracy
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Solution Overview
Problem
Existing DNA polymerases with exonuclease activity can compromise sequencing accuracy by hydrolyzing incorporated modified nucleotides, and commercially available exonuclease-deficient mutants retain significant exonuclease activity, limiting their effectiveness in applications like sequencing by synthesis.
Innovation Solution
Development of exo−/exo− DNA polymerase variants with specific amino acid mutations that reduce exonuclease activity to negligible levels, ensuring minimal primer degradation and improved sequencing accuracy by maintaining high polymerase activity while eliminating exonuclease activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If exonuclease activity is present in DNA polymerase, then proofreading capability is improved, but modified nucleotides are hydrolyzed compromising incorporation regimen
Solution Approach 1:
The invention extracts and removes the exonuclease function from the DNA polymerase enzyme through site-directed mutagenesis of critical residues (D141A and E143A in Motif I). This creates an exonuclease-deficient polymerase that retains DNA synthesis capability while eliminating the harmful hydrolysis of modified nucleotides, thereby resolving the contradiction between proofreading capability and modified nucleotide stability.
2Object-generated harmful factors
If exonuclease-deficient mutants are created, then modified nucleotide stability is improved, but residual exonuclease activity remains limiting effectiveness
Solution Approach 1:
The invention applies parameter changes by mutating two critical aspartate residues (D141 and E143) in the exonuclease active site to alanine. This double mutation dramatically reduces exonuclease activity to negligible levels while preserving polymerase function, thereby eliminating residual exonuclease activity that limits sequencing effectiveness and improving both modified nucleotide stability and sequencing accuracy.
3Productivity
If wild-type polymerase is used, then polymerase activity is maintained, but phasing errors occur due to primer degradation
Solution Approach 1:
The invention converts the potentially harmful exonuclease activity into a benefit by completely eliminating it through double mutation. This prevents primer degradation and phasing errors during sequencing, thereby improving sequencing read quality and accuracy while maintaining high polymerase activity for efficient DNA synthesis.
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 exo−/exo− variants significantly reduce phasing errors, enhance sequencing read quality, and increase read length by minimizing primer degradation, resulting in higher fidelity and longer sequencing reads compared to wild-type enzymes.
Implementation Method 1
DNA polymerases catalyze DNA polymerization
Implementation Method 2
transfers the primer strand from the polymerase domain to the 3′-5′ exonuclease active site
Data Source
AI summary
Compositions and methods are described to modify Family B DNA polymerases that contain residual exonuclease activity that interferes with sequencing techniques and with detection of single nucleotide polymorphisms. The compositions are mutant proteins with reduced exonuclease activity compared with presently available “exo−” polymerases, and a sensitive screening assay that enables an assessment of exonuclease activity of any synthetic DNA polymerase.