Recombinant Ferrochelatase (hemH)
Description
Definition and Biological Role of Recombinant Ferrochelatase (hemH)
Recombinant ferrochelatase (hemH) refers to the genetically engineered form of the enzyme ferrochelatase, encoded by the hemH gene, which catalyzes the final step in heme biosynthesis: the insertion of ferrous iron (Fe²⁺) into protoporphyrin IX to form protoheme . This metalloenzyme is critical across eukaryotes and prokaryotes, with variations in substrate specificity and localization. In Gram-positive bacteria like Bacillus subtilis, hemH homologs (e.g., CpfC) catalyze iron insertion into coproporphyrin III , while eukaryotic ferrochelatases predominantly act on protoporphyrin IX in mitochondria . Recombinant production enables large-scale studies and biotechnological applications, such as optimizing heme synthesis in microbial systems .
Domain Architecture
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Core structure: Composed of two Rossmann-fold domains forming the active site, conserved across species .
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CAB domain: Present in cyanobacterial and plant type II ferrochelatases (e.g., Synechocystis sp. PCC 6803), this C-terminal chlorophyll a/b-binding domain regulates enzyme activity and substrate flux .
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Metal-sensitive loop: A flexible loop (residues Q302–Q314 in humans) modulates substrate entry and product release .
Table 2: Expression Systems and Yields
Kinetic Parameters
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Full-length FeCh: K<sub>M</sub> = 12.5 µM (protoporphyrin IX), k<sub>cat</sub> = 1.2 min⁻¹ .
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FeChΔ347: K<sub>M</sub> = 18.9 µM, k<sub>cat</sub> = 3.6 min⁻¹ .
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Human ferrochelatase: Inhibited by nitric oxide and redox modifications (e.g., glutathionylation) .
Regulatory Interactions
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Substrate competition: CAB domain in cyanobacterial ferrochelatase directs porphyrin flux toward chlorophyll synthesis, reducing heme output .
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Transcriptional control: In E. coli, hemH overexpression represses upstream heme pathway genes (e.g., hemA, hemL), reducing δ-aminolevulinic acid (ALA) accumulation .
Heme-Binding Protein Production
Co-expression of recombinant ferrochelatase with heme-binding proteins (e.g., nitric oxide synthase) ensures complete heme incorporation, critical for structural and commercial applications .
Table 3: Applications in Metabolic Engineering
| Application | Strategy | Outcome |
|---|---|---|
| ALA overproduction | Overexpress hemA, hemL, hemD | 3.25 g/L ALA in E. coli |
| Heme protein purity | Co-express hemH with target | 100% heme incorporation |
Industrial Scale-Up
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Ferrochelatase variants lacking regulatory domains (e.g., CAB) enhance heme yields in photosynthetic microbes .
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Redox-sensitive residues (e.g., C395 in humans) are targets for optimizing activity under industrial conditions .
Research Gaps and Future Directions
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Mechanistic details: The role of the [2Fe-2S] cluster in eukaryotic ferrochelatase redox sensing remains unclear .
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Chaperone interactions: Heme trafficking partners post-release from ferrochelatase are unidentified .
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CAB domain ligands: Pigment binding to the CAB domain hypothesized to regulate chlorophyll/heme balance requires direct evidence .
Product Specs
Target Background
KEGG: ecv:APECO1_1540
