Recombinant Edwardsiella ictaluri NAD-dependent malic enzyme (maeA), partial
Description
Enzymatic Characteristics and Activity
NAD-dependent malic enzymes (NAD-MEs) are critical in bacterial metabolism. In Escherichia coli, MaeA exhibits dual activity:
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Malic enzyme activity: Converts malate to pyruvate with NAD⁺ reduction ( for malate: ~0.5 mM) .
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Fumarase activity: Catalyzes fumarate hydration to malate ( for fumarate: 13 mM) .
This bifunctionality is conserved in human ME2 but absent in NADP-dependent malic enzymes like MaeB . Structural studies suggest that substrate binding pockets and regulatory domains determine activity specificity. For example, fumarate inhibits malate conversion in E. coli MaeA, indicating competitive substrate interactions .
Recombinant Expression Systems
Recombinant MaeA is typically expressed in heterologous hosts for large-scale production:
| Host System | Yield | Advantages | Source |
|---|---|---|---|
| E. coli | High | Cost-effective, rapid purification | |
| Yeast | Moderate | Eukaryotic post-translational modifications | |
| Insect cells | Low | Complex glycosylation possible |
E. ictaluri MaeA has not been explicitly characterized, but Salmonella choleraesuis MaeA (65% sequence similarity) serves as a functional proxy. Its recombinant form (partial sequence: residues 1–565) retains activity when expressed in E. coli with a His-tag for affinity purification .
Applications in Vaccine Development
While E. ictaluri MaeA is not directly linked to vaccine platforms, its genomic context in balanced-lethal systems highlights its potential:
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Balanced-lethal systems: E. ictaluri ΔasdA mutants require plasmid-borne asdA for survival, enabling stable antigen expression .
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Antigen delivery: Recombinant enzymes like MaeA could be engineered to secrete immunogenic peptides via type II secretion systems .
Research Gaps and Future Directions
Key unknowns about E. ictaluri MaeA include:
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Kinetic parameters: Substrate affinity, pH/thermal stability.
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Structural data: Crystal structures to elucidate fumarase activity.
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Regulatory mechanisms: Allosteric effectors (e.g., CoA, fumarate) observed in Arabidopsis NAD-MEs .
Comparative studies with Salmonella and E. coli homologs are essential to advance industrial or therapeutic applications .
