Modified Polymerases for Single Molecule Sequencing Accuracy
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Current DNA polymerases face challenges in single molecule sequencing due to high branching fraction, instability of closed polymerase-DNA complexes, and rapid catalytic cycle steps, which affect sequencing accuracy and processivity.
Innovation Solution
Modified recombinant DNA polymerases with specific mutations, such as those in the Φ29-type polymerase, exhibit reduced branching fraction, increased stability of closed complexes, and slowed catalytic cycle steps, improving processivity and sequencing accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wild-type DNA polymerase is used in single molecule sequencing, then the catalytic cycle proceeds rapidly, but the branching fraction is high and sequencing accuracy deteriorates
Solution Approach 1:
The patent applies parameter changes by modifying the catalytic rate constants of the polymerase through site-directed mutagenesis. Specifically, mutations are introduced to reduce k2 (isomerization rate) and k3 (phosphate release rate) to create observable pauses in the catalytic cycle, allowing sufficient time for detection of nucleotide incorporation events while maintaining overall sequencing capability
2Productivity
If DNA polymerase exhibits rapid catalytic steps, then processivity is maintained, but the stability of closed polymerase-DNA complexes is insufficient
Solution Approach 1:
The patent uses parameter changes to optimize the balance between processivity and complex stability. Mutations are designed to specifically stabilize the closed complex state (increasing the population of closed complexes) while preserving the overall processivity of the polymerase through careful selection of residue positions that affect complex stability without disrupting catalytic function
3Productivity
If standard DNA polymerase is used, then nucleotide incorporation occurs efficiently, but branching fraction is high causing sequencing errors
Solution Approach 1:
The patent applies parameter changes by modifying the branching fraction through specific mutations that alter the kinetics of nucleotide incorporation. The mutations reduce the branching fraction (the proportion of incorrect incorporations) while maintaining efficient incorporation of correct nucleotides, thereby improving sequencing accuracy without sacrificing productivity
Solution Approach 2:
The patent implements feedback mechanisms by creating polymerases with slowed catalytic steps that allow real-time monitoring and detection of incorporation events. The reduced rate constants create observable pauses that enable the sequencing system to detect and verify correct nucleotide incorporation before proceeding, effectively using kinetic feedback to improve accuracy
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
These modifications lead to enhanced sequencing accuracy and processivity, allowing for more reliable and precise DNA sequencing by reducing errors and increasing the stability and efficiency of the polymerization process.
Implementation Method 1
DNA polymerases replicate the genomes of living organisms... DNA polymerases are also ubiquitous tools of biotechnology... for reverse transcription, amplification, labeling, and sequencing
Data Source
Figure 1A~1B
Figure 2A~2B
Figure 3
AI summary
Provided are compositions comprising modified recombinant polymerases that exhibit branching fractions that are less than the branching fractions of the polymerases from which they were derived, or branching fractions that are less than about 25% for a phosphate-labeled nucleotide analog. Also provided are compositions comprising modified recombinant polymerases that exhibit closed polymerase/DNA complexes with increased stability relative to the parental polymerase. Also provided are compositions comprising modified recombinant polymerases that exhibit decreased rate constants relative to the parental polymerases. Provided are methods for generating polymerases with the aforementioned phenotypes. Provided are methods of using such polymerases to make a DNA or to sequence a DNA template.