Recombinant Yeast NADPH-Dependent Reductive TCA Pathway
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Solution Overview
Problem
The reductive TCA pathway in yeast cells for succinate production faces a redox imbalance due to the consumption of NADH, leading to reduced succinate yield and potential adverse effects on cell health and productivity.
Innovation Solution
Development of recombinant yeast cells with an active reductive TCA pathway that oxidizes NADPH to NADP+, utilizing NADPH-dependent enzymes and increased flux through the pentose phosphate pathway to provide NADPH, thereby avoiding NADH consumption and maintaining redox balance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If the reductive TCA pathway is used for succinate production, then succinate yield is improved, but redox imbalance occurs due to NADH consumption
Solution Approach 1:
The invention changes the cofactor parameter from NADH-dependent to NADPH-dependent for the malate dehydrogenase and fumarate reductase enzymes. This parameter change allows the pathway to use NADPH instead of NADH, resolving the redox imbalance while maintaining high succinate yield through the reductive TCA pathway
Solution Approach 2:
The invention introduces NADPH as an intermediary cofactor to mediate the reduction reactions in the TCA pathway. By using NADPH-dependent enzymes instead of NADH-dependent enzymes, the system avoids the redox imbalance problem while achieving efficient succinate production
2Productivity
If NADH-dependent enzymes are used in the reductive TCA pathway, then pathway activity is improved, but cell health deteriorates due to redox imbalance
Solution Approach 1:
The invention changes the cofactor specificity parameter of the enzymes from NADH-dependent to NADPH-dependent. This parameter change maintains high pathway activity for succinate production while avoiding the harmful redox imbalance that would otherwise damage cell health
3Reliability
If oxidative TCA pathway is used to balance redox, then redox balance is improved, but succinate yield decreases
Solution Approach 1:
The invention changes the cofactor parameter of the reductive TCA pathway enzymes to NADPH-dependent, allowing the pathway to maintain its high succinate-yielding reductive mode while achieving redox balance through NADPH oxidation instead of switching to the oxidative pathway
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 approach enhances succinate yield and improves cell health and productivity by mitigating redox imbalances and ensuring efficient NADPH production for the reductive TCA pathway.
Implementation Method 1
NADPH-dependent malate dehydrogenase that converts oxaloacetate to malate
Implementation Method 2
NADPH-dependent fumarate reductase that converts fumarate to succinate
Implementation Method 3
increased flux through the pentose phosphate pathway to provide NADPH
Data Source
AI summary
Recombinant yeast cells contain a reductive TCA pathway from phosphoenolpyruvate or pyruvate to succinate. At least one metabolic step in the pathway includes a reaction of NADPH to produce NADP+. The yeast cell contains at least one exogenous NADPH-dependent gene in the pathway from phosphoenolpyruvate or pyruvate to succinate, preferably an NADPH-dependent malate dehydrogensase or fumarate reducase gene (or both).