Recombinant Escherichia coli O8 Phosphoserine aminotransferase (serC)
Description
Biochemical Characteristics of SerC
Catalytic Function:
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Converts 3-phosphohydroxypyruvate + L-glutamate ⇌ O-phosphoserine + α-ketoglutarate
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Crystal structure resolved at 2.3 Å resolution (PDB: 1BJO), revealing a homodimeric architecture with conserved PLP-binding domains
Kinetic Parameters:
| Substrate | Kₘ (mM) | k<sub>cat</sub> (s⁻¹) | Source |
|---|---|---|---|
| 3-phosphohydroxypyruvate | 0.12 | 15.8 | Engineered E. coli |
| L-glutamate | 1.45 | 14.2 | Engineered E. coli |
Genetic Regulation and Modifications
Operon Structure:
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serC resides in the serC-aroA operon, co-transcribed with aroA (involved in aromatic amino acid biosynthesis) .
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Regulatory elements include CRP-binding sites upstream of serC, influencing expression under amino acid starvation .
Engineering Strategies:
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Feedback Resistance: Mutations in SerA (phosphoglycerate dehydrogenase) combined with serC overexpression enhance O-phosphoserine production. For example, strain CA07-0012 with serA(G336V) and serC activation produced 18.7 g/L O-phosphoserine in 48 hours .
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Codon Optimization: Modifying the serC initiation codon from ATG to CTG reduced phosphoserine phosphatase activity by 40%, redirecting flux toward O-phosphoserine accumulation .
Industrial Applications
Metabolic Engineering:
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O-Phosphoserine Production: Recombinant E. coli O8 strains with serC overexpression achieve titers up to 23.4 g/L under optimized conditions (Table 1) .
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Vitamin B₆ Biosynthesis: Engineered SerC variants distribute metabolic flux between serine and pyridoxine pathways, boosting vitamin B₆ yields by 2.7-fold .
Table 1: Productivity of O-phosphoserine in engineered E. coli strains
| Strain | SerA Mutation | SerC Activation | O-Phosphoserine (g/L) |
|---|---|---|---|
| CA07-0012 (wild-type) | None | No | 3.2 |
| CA07-0012 + pCL-Prmf-serA* | G336V | Yes | 18.7 |
| CA07-0012 + pCL-Prmf-serA* + serC | G336V | Yes | 23.4 |
Clinical Relevance in E. coli O8 Pathogenesis
Epidemiology:
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O8 is the fifth most prevalent O-serotype (5%) among invasive E. coli infections in adults ≥60 years .
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Associated with multidrug-resistant (MDR) lineages like ST58 and ST10, conferring resistance to fluoroquinolones and third-gen cephalosporins .
Vaccine Target:
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O8 is not covered by the ExPEC4V or ExPEC9V vaccine candidates, highlighting unmet needs in vaccine design .
Research Advancements and Challenges
Key Findings:
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Cross-Resistance: serC mutations in E. coli O8 confer cross-resistance to heat stress via PhoPQ-RpoS signaling .
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Heterologous Expression: Mycobacterium tuberculosis serC complements E. coli SerC deficiency, restoring growth in serine-free media .
Challenges:
Product Specs
Target Background
KEGG: ecr:ECIAI1_0947
