Acetoacetyl-CoA Reductase Variants for PHA Yield
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Solution Overview
Problem
Current methods for producing polyhydroxyalkanoates (PHAs) in microorganisms, such as Ralstonia eutropha, face limitations in yield and efficiency due to constraints in the acetoacetyl-CoA reductase enzyme, which affects the synthesis and accumulation of these biopolymers.
Innovation Solution
Development of acetoacetyl-CoA reductase variants with specific mutations, such as valine to isoleucine at position 141, methionine to threonine at position 12, and glutamic acid to lysine at position 42, along with their coding genes, are introduced into microorganisms to enhance PHA production, combined with modifications like expressing PHA polymerase variants and enhancing (R)-enoyl-CoA hydratase activity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If wild-type acetoacetyl-CoA reductase is used in PHA synthesis, then the basic enzymatic function is maintained, but the PHA yield and production efficiency are limited
Solution Approach 1:
The patent applies parameter changes by systematically mutating specific amino acid residues in the acetoacetyl-CoA reductase enzyme (positions 12, 42, 55, 141, and 194) to optimize its catalytic properties. These point mutations alter the enzyme's kinetic parameters and substrate affinity, thereby enhancing PHA production efficiency while preserving the core enzymatic function through rational protein engineering
2Productivity
If acetoacetyl-CoA reductase variants with multiple mutations are introduced to enhance PHA production, then the PHA yield increases significantly, but the complexity of strain construction and characterization increases
Solution Approach 1:
The patent employs segmentation by dividing the enzyme optimization process into independent point mutations at specific positions (12, 42, 55, 141, 194). Each mutation can be independently constructed and characterized, allowing systematic optimization without requiring simultaneous modification of multiple sites, thereby reducing the overall complexity of strain construction
3Quantity of substance
If metabolic pathways are enhanced to improve PHA accumulation, then the PHA content in biomass increases, but the biomass growth may be compromised due to carbon source allocation
Solution Approach 1:
The patent utilizes parameter changes by optimizing the acetoacetyl-CoA reductase enzyme's catalytic efficiency through amino acid mutations. This enhances the conversion rate of acetoacetyl-CoA to 3-hydroxybutyryl-CoA, improving PHA accumulation without requiring excessive carbon source allocation, thereby maintaining a better balance between biomass growth and PHA content
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 modified microorganisms exhibit significantly increased biomass and PHA content, leading to improved yields and fermentation production efficiency, reducing production costs and providing new strain resources for PHA development.
Implementation Method 1
acetoacetyl-CoA reductase (PhaB) variant... synthesizes 3-hydroxybutyric acid by the action of phaB (acetoacetyl-CoA reductase)
Data Source
AI summary
Provided is engineered microorganisms expressing acetoacetyl-CoA reductase variants and a method for improving the yield of PHA. Compared with the wild-type acetoacetyl-CoA reductase represented by SEQ ID NO. 31, the variant has one or more of the following mutations: (1) mutation of valine at position 141 to isoleucine or leucine; (2) mutation of methionine at position 12 to threonine, serine, alanine, leucine, lysine or isoleucine; (3) mutation of isoleucine at position 194 to valine, leucine or methionine; (4) mutation of glutamic acid at position 42 to lysine, glutamine, leucine, aspartic acid, proline, threonine, asparagine, or histidine; and (5) mutation of phenylalanine at position 55 to valine, alanine or isoleucine. The variants and their coding genes can promote the synthesis and accumulation of PHA by the strain and increase the yield of PHA.