Genetically Engineered E. coli for Citramalate Production
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Solution Overview
Problem
Current methods for producing citramalate in E. coli are inefficient, as existing strains struggle to accumulate significant amounts due to metabolic pathways that divert pyruvate and acetyl-CoA into other products, limiting citramalate yield and accumulation.
Innovation Solution
Genetically engineered E. coli strains are developed with reduced expression of citrate synthase and specific knockout mutations in genes like gltA and ackA, along with overexpression of citramalate synthase, to redirect metabolic flux and increase acetyl-CoA availability, thereby enhancing citramalate production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wild type citrate synthase is present in E. coli, then the TCA cycle functions normally, but acetyl-CoA is diverted to citrate production instead of citramalate, reducing citramalate yield
Solution Approach 1:
The patent removes or reduces the function of wild type citrate synthase (through knockout or downregulation) to extract the harmful metabolic flux that diverts acetyl-CoA away from citramalate production. This allows acetyl-CoA to remain available for the heterologous citramalate synthase reaction, directly resolving the contradiction between TCA cycle function and citramalate yield
Solution Approach 2:
The patent changes the metabolic parameter of citrate synthase activity by introducing mutations (e.g., F383L, F383V, F383M, D362V, D362I) that reduce its catalytic efficiency. This parameter change allows partial preservation of TCA cycle function while redirecting sufficient acetyl-CoA flux toward citramalate production, achieving a balance between both requirements
2Productivity
If pyruvate and acetyl-CoA are available for citramalate synthesis, then citramalate production increases, but these substrates are diverted into other metabolic pathways, limiting accumulation
Solution Approach 1:
The patent converts the harmful metabolic flux that normally diverts substrates into byproducts into a beneficial pathway for citramalate accumulation. By engineering the metabolic network to favor citramalate synthase activity and block competing pathways (through knockout or downregulation of alternative enzymes), the substrates that would have formed byproducts are instead channeled into citramalate production
Solution Approach 2:
The patent removes or reduces the activity of competing metabolic pathways (such as those converting pyruvate to lactate or acetyl-CoA to acetate) to extract the harmful competitive flux. This ensures that pyruvate and acetyl-CoA are preferentially directed toward citramalate synthesis, resolving the contradiction between production rate and byproduct formation
3Productivity
If citrate synthase activity is reduced to increase acetyl-CoA for citramalate, then citramalate yield improves, but TCA cycle function is compromised
Solution Approach 1:
The patent applies local quality by creating a specialized metabolic compartment or pathway optimization where citrate synthase activity is specifically reduced only in the context of citramalate production, while maintaining sufficient TCA cycle function for cellular metabolism. This is achieved through targeted mutations or conditional downregulation that preserves essential TCA functions while redirecting flux for product synthesis
Solution Approach 2:
The patent applies partial action by reducing rather than completely eliminating citrate synthase activity. This partial reduction is sufficient to redirect adequate acetyl-CoA flux toward citramalate production while maintaining enough TCA cycle function to support cellular metabolism, achieving a balance that resolves the contradiction between yield and reliability
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 engineered strains achieve high citramalate yields, with concentrations reaching up to 46.5 g/L in fed-batch processes, approaching 75% of the theoretical maximum from glucose, while minimizing byproduct formation like acetate.
Implementation Method 1
a first exogenous polynucleotide encoding a citramalate synthase which catalyzes the condensation of acetyl CoA and pyruvic acid
Implementation Method 2
a second exogenous polynucleotide encoding a citrate synthase which catalyzes the condensation of acetyl CoA and oxaloacetate
Data Source
AI summary
Provided herein is a genetically engineered microbe which accumulates citramalate. In one embodiment, the microbe includes an exogenous polynucleotide encoding a citramalate synthase which catalyzes the condensation of acetyl CoA and pyruvic acid. Optionally, the microbe also includes a second exogenous polynucleotide encoding a citrate synthase which catalyzes the condensation of acetyl CoA and oxaloacetate, and the citrate synthase activity in the microbe is reduced compared to a control microbe. In one embodiment, the citrate synthase includes at least one amino acid substitution in the acetyl-CoA binding pocket, the mobile loop, the NADH binding site, and the oxaloacetate binding site, or a combination thereof. Also provided herein are methods for using the genetically engineered microbe, including a method for producing citramalate. The method can further include isolating the citramalate.