L-Cysteine Production via Thermophilic Enzyme Segmentation
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Solution Overview
Problem
Conventional fermentation methods for producing L-cysteine face challenges such as growth inhibition of microorganisms and feedback inhibition by L-cysteine, and existing enzyme-based methods struggle with efficient activity at neutral pH conditions.
Innovation Solution
A method involving the combination of heat-resistant enzymes, specifically 3-phosphoglycerate dehydrogenase (PGDH) and phosphoserine aminotransferase (PSAT) derived from thermophilic bacteria, is used to synthesize O-phosphoserine from 3-phosphoglyceric acid, which is then converted into L-cysteine, allowing for enzyme design to avoid feedback inhibition and operate effectively at pH 6 to 8.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If L-cysteine is produced by fermentation method using microorganisms, then L-cysteine can be synthesized through metabolic pathways, but growth inhibition of microorganisms and feedback inhibition to biosynthetic enzymes occur as intracellular concentration increases
Solution Approach 1:
The invention divides the L-cysteine production process into two separate systems: (1) a fermentation system where microorganisms synthesize L-cysteine precursors and export them extracellularly, and (2) a separate conversion system where the accumulated extracellular precursors are converted to L-cysteine. This segmentation prevents intracellular accumulation that causes feedback inhibition and growth inhibition, allowing continuous precursor production without compromising microorganism health or enzyme activity.
Solution Approach 2:
The invention uses extracellular L-cysteine precursors as intermediary substances that mediate between the fermentation system and the conversion system. These precursors accumulate in the extracellular space rather than intracellularly, serving as a buffer that decouples the production rate from the conversion rate, thereby avoiding feedback inhibition while maintaining continuous production.
2Reliability
If enzyme-based production method is used to avoid growth inhibition, then L-cysteine can be produced without microorganism cultivation limits, but existing enzymes lack sufficient activity at neutral pH conditions
Solution Approach 1:
The invention changes the pH parameter condition for enzyme operation from extreme pH (where existing thermophilic enzymes show activity) to neutral pH (pH 6-8), which is more suitable for industrial applications. This is achieved by selecting and optimizing enzymes that maintain high catalytic activity specifically in the neutral pH range, thereby achieving both system stability and high productivity under physiologically compatible conditions.
3Productivity
If conventional fermentation method is used, then L-cysteine production can proceed through natural metabolic pathways, but feedback inhibition mechanism reduces biosynthetic enzyme activity when L-cysteine concentration increases
Solution Approach 1:
The invention extracts the L-cysteine precursor production function from the complete L-cysteine synthesis pathway. By using enzymes that catalyze only the early steps (producing precursors like O-acetylserine or L-cysteine-γ-semialdehyde) and stopping before final L-cysteine formation, the system produces intermediates that do not trigger feedback inhibition, while still enabling efficient L-cysteine production in the separate conversion system.
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 in vitro production of L-cysteine, avoiding growth inhibition and feedback issues, and allows for flexible pathway design to enhance productivity.
Implementation Method 1
3-phosphoglycerate dehydrogenase (hereinafter, referred to as "PGDH" in principle) that converts 3-phosphoglyceric acid to phosphohydroxypyruvic acid
Implementation Method 2
phosphoserine aminotransferase (hereinafter, referred to as "PSAT" in principle) that converts phosphohydroxypyruvic acid to O-phosphoserine
Implementation Method 3
the obtained recombinant bacterial cells or an extract from bacterial cells is subjected to a heat treatment at around 60 to 90°C to inactivate an enzyme derived from a host and further to partially destroy a cell structure of the host
Data Source
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AI summary
An object of the present invention is to provide a novel method for producing L-cysteine in place of a conventional fermentation method. More specifically, the object is to provide a method for producing L-cysteine by the combination of heat-resistant enzymes. In particular, the object is to provide a method for efficiently producing a pathway for synthesizing O-phosphoserine from 3-phosphoglyceric acid (3PG) via phosphohydroxypyruvic acid (HPV). The present invention solved the problem by a method for producing O-phosphoserine including acting phosphoserine aminotransferase (PSAT) and 3-phosphoglycerate dehydrogenase (PGDH) that are each derived from a thermophilic bacterium on 3 PG to generate O-phosphoserine, and a method for producing L-cysteine including the step described above.