Recombinant Escherichia coli L-threonine 3-dehydrogenase (tdh)
Description
Biochemical Properties
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Function: The tdh enzyme catalyzes the NAD⁺-dependent conversion of L-threonine to 2-amino-3-ketobutyrate, which spontaneously decarboxylates to aminoacetone .
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Structure: Recombinant tdh retains its native tetrameric structure, with a molecular mass of approximately 155 kDa .
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Optimal Conditions:
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Kinetics:
Role in E. coli Metabolism
The tdh enzyme is integral to L-threonine degradation pathways in E. coli. Its activity:
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Regulates Threonine Levels: Converts excess L-threonine into intermediates that feed into the TCA cycle .
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Competes with Biosynthesis: Deletion of tdh (Δtdh) redirects metabolic flux toward L-threonine accumulation, enhancing biosynthesis yields .
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Links to Isoleucine Production: Repression of tdh activity increases carbon flow through the aspartate pathway, boosting L-isoleucine synthesis .
Threonine Overproduction
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Deleting or inactivating tdh in E. coli strains increases L-threonine yields by 27.7% in engineered strains .
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A Δtdh mutant strain achieved 82.4 g/L threonine in fed-batch fermentation .
2,5-Dimethylpyrazine (2,5-DMP) Synthesis
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TDH catalyzes the first step (L-threonine → aminoacetone) in 2,5-DMP biosynthesis .
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Overexpression of tdh in Bacillus subtilis increased 2,5-DMP production from 0.03 mM to 4.40 mM .
L-Isoleucine Production
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Simultaneous deletion of tdh, ltaE, and yiaY genes in E. coli elevated L-isoleucine yields by 72.3% (7.48 g/L) .
Recombinant Production Systems
Recombinant tdh is produced in:
Research Findings
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Thermostable Variants: A recombinant tdh from Thermococcus kodakaraensis exhibited optimal activity at 90°C and pH 12 .
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Metabolic Engineering: Transcriptome analysis revealed that Δtdh strains upregulate aspartate pathway genes, enhancing carbon flux toward L-isoleucine .
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Coenzyme Utilization: The enzyme requires NAD⁺ for catalysis, with activity inhibited by EDTA .
Industrial Relevance
Recombinant tdh is critical for:
Product Specs
Target Background
KEGG: eck:EC55989_4083
