Recombinant Prochlorococcus marinus Triosephosphate isomerase (tpiA)
Description
Enzymatic Function and Catalytic Mechanism
tpiA in P. marinus (UniProt: Q31AR4) is annotated as a triosephosphate isomerase involved in gluconeogenesis . Key features include:
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Reaction specificity: Stereospecific conversion of DHAP to G3P, ensuring carbon flux through central metabolic pathways.
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Structural conservation: TIMs typically adopt an (α/β)₈-barrel fold with a conserved catalytic glutamate residue. While the P. marinus TIM structure remains unresolved, homology modeling based on Trypanosoma brucei TIM (RMSD: 1.12 Å for 487 Cα positions ) suggests similar active-site geometry.
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Thermodynamic efficiency: TIMs exhibit near-perfect catalytic proficiency, with reaction rates limited only by substrate diffusion .
Genomic and Metabolic Context
The tpiA gene is part of the compact genome of P. marinus CCMP1375 (1.75 Mbp, 1,931 genes ):
| Genomic Feature | Value |
|---|---|
| Genome size | 1,751,080 bp |
| Protein-coding genes | 1,885 |
| tpiA location | Chromosome (RefSeq: NC_005042.1) |
| GC content | 36.82% |
| Predicted protein length | ~248 residues |
P. marinus lacks a complete tricarboxylic acid (TCA) cycle , making glycolysis/gluconeogenesis critical for carbon metabolism. The absence of 2-oxoglutarate dehydrogenase necessitates tight regulation of TIM to balance carbon partitioning .
Comparative Analysis with Other TIMs
Notably, P. marinus TIM shares higher sequence divergence with pathogenic eukaryotes (~53% identity with T. brucei ) but maintains conserved active-site residues.
Biotechnological and Ecological Implications
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Carbon cycling: As a dominant primary producer, P. marinus relies on TIM for optimizing carbon use efficiency in oligotrophic oceans .
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Recombinant applications: Heterologous expression of tpiA could enhance metabolic engineering in algal biofuels, though structural studies are needed to resolve stability under varying pH/temperature .
Unresolved Questions
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Structural dynamics: The "flexible loop" conformation (residues 168–174 in humans ) remains uncharacterized in P. marinus.
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Genetic variants: No mutations analogous to human Glu104Asp or Phe240Ile (linked to enzyme dysfunction ) have been reported in P. marinus.
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Regulatory mechanisms: How TIM activity is modulated in response to nutrient scarcity or light fluctuations warrants further study .
Product Specs
Target Background
KEGG: pme:NATL1_10641
STRING: 167555.NATL1_10641
