Acetyl-CoA Production Cycle via CO2 Fixation
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Solution Overview
Problem
Existing carbon dioxide fixation cycles for producing acetyl-CoA are inefficient due to low enzyme activity, side reactions, and difficulty in introducing enzymes into non-anaerobic microorganisms, leading to challenges in constructing and regulating complex pathways.
Innovation Solution
Introducing enzymatic activities of malate thiokinase, malyl-CoA lyase, glyoxylate carboligase, and 2-hydroxy-3-oxopropionate reductase into microorganisms like Escherichia coli and Corynebacterium glutamicum to create a simplified acetyl-CoA production cycle that efficiently converts carbon dioxide into acetyl-CoA without consuming it.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If existing carbon dioxide fixation cycles (Calvin-Benson cycle, reductive TCA cycle, Wood-Ljungdahl pathway) are introduced to microorganisms, then CO2 fixation capability is achieved, but the pathway complexity and number of enzymes required increases significantly
Solution Approach 1:
The patent extracts and implements only the essential CO2 fixation steps from complex natural cycles, using a minimal set of enzymes (pyruvate synthase, acetyl-CoA synthase) to achieve the core function of converting CO2 to acetyl-CoA, thereby eliminating unnecessary pathway complexity while maintaining CO2 fixation capability
Solution Approach 2:
The patent utilizes the microorganism's existing metabolic pathways and enzymes to support the CO2 fixation process, rather than introducing complete external cycles. The microorganism's native metabolism provides auxiliary functions such as energy generation and precursor supply, reducing the need for additional complex pathway components
2Productivity
If complete carbon dioxide fixation cycles are introduced, then CO2 fixation efficiency improves, but the difficulty of constructing and regulating the pathway increases
Solution Approach 1:
The patent extracts only the critical CO2 fixation reactions from complete cycles, implementing a streamlined pathway that achieves high CO2 fixation efficiency with minimal enzymes. This extraction approach simplifies genetic construction and regulatory control while maintaining productive CO2 conversion to acetyl-CoA
Solution Approach 2:
The CO2 fixation pathway is segmented into discrete, manageable enzymatic steps that can be independently introduced and regulated. The patent divides the process into specific reactions catalyzed by individual enzymes, allowing for modular genetic engineering and easier pathway construction compared to introducing complete cyclic pathways
3Reliability
If enzymes for carbon dioxide fixation are introduced into non-anaerobic microorganisms, then CO2 fixation capability is achieved, but side reactions and low enzyme activity occur
Solution Approach 1:
The patent uses pyruvate as an intermediary substrate that bridges CO2 fixation and the microorganism's existing aerobic metabolism. Pyruvate synthase catalyzes CO2 fixation to form pyruvate, which then enters native metabolic pathways, avoiding the need to introduce complete anaerobic cycles and reducing harmful side reactions
Solution Approach 2:
The patent changes the operational parameters of the CO2 fixation pathway by using enzymes and conditions compatible with aerobic environments. The selected enzymes function optimally under aerobic conditions, and the pathway is integrated with the microorganism's native metabolism to maintain appropriate redox balance and avoid side reactions associated with anaerobic conditions
4Reliability
If multiple enzymes for carbon dioxide fixation are introduced, then CO2 fixation pathway functionality is achieved, but the number of genes to be introduced and regulated increases
Solution Approach 1:
The patent extracts the minimal essential enzymatic functions needed for CO2 fixation, implementing only pyruvate synthase and acetyl-CoA synthase activities. This extraction of core functionality reduces the number of genes to be introduced from dozens (in complete cycles) to just one or two key enzymes, significantly simplifying genetic engineering while maintaining pathway functionality
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 enables efficient production of acetyl-CoA and its derivatives, such as acetone, isopropyl alcohol, and glutamic acid, by simplifying the carbon dioxide fixation pathway and reducing the number of enzymes required, thus overcoming previous inefficiencies and complexity issues.
Implementation Method 1
CO2 is fixed by ribulose-1,5-bisphosphate carboxylase (RubisCO) and, ultimately, glyceraldehyde 3-phosphate is produced
Implementation Method 2
pyruvate is converted into acetyl-CoA by the action of the enzymes pyruvate decarboxylase, pyruvate formate-lyase
Implementation Method 3
The sugar is first converted into pyruvate via a metabolic pathway called the glycolytic pathway, such as the Embden-Meyerhof pathway, the Entner-Doudoroff pathway, or the pentose phosphate pathway
Data Source
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AI summary
An acetyl-CoA producing microorganism obtained by imparting at least one enzymatic activity selected from the group consisting of malate thiokinase, malyl-CoA lyase, glyoxylate carboligase, 2-hydroxy-3-oxopropionate reductase, and hydroxypyruvate reductase, to a microorganism that does not have any of the following (a), (b), (c), (d) or (e): (a) a carbon dioxide fixation cycle including an enzymatic reaction from malonyl-CoA to malonate semialdehyde or 3-hydroxypropionate; (b) a carbon dioxide fixation cycle including an enzymatic reaction from acetyl-CoA and CO2 to pyruvate; (c) a carbon dioxide fixation cycle including an enzymatic reaction from crotonyl-CoA and CO2 to ethylmalonyl-CoA or glutaconyl-CoA; (d) a carbon dioxide fixation cycle including an enzymatic reaction from CO2 to formate; or (e) at least one selected from the group consisting of malate thiokinase and malyl-CoA lyase.