Recombinant Cytochrome c oxidase polypeptide 4 (ctaF)
Description
Overview of Recombinant Cytochrome c Oxidase Polypeptide 4 (ctaF)
Recombinant Cytochrome c oxidase polypeptide 4 (ctaF) is a nuclear-encoded subunit of cytochrome c oxidase (COX), the terminal enzyme of the mitochondrial electron transport chain. It plays a critical role in assembling and stabilizing the COX complex, which catalyzes the transfer of electrons to oxygen, producing water and generating a proton gradient for ATP synthesis . Recombinant ctaF is produced in bacterial systems (e.g., Corynebacterium glutamicum, Streptomyces avermitilis) and is used in biochemical and structural studies to investigate COX function and regulation .
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HITERRTDVLPEDWEEAEVADKAGTLGFFSPGSIWPAAMSGAVGLLGFGIIFMHYWLILV
GALALTYTIAKLNFQYGVPREKH
Assembly and Stabilization of COX Complex
ctaF is essential for the proper assembly of COX, as demonstrated in RNA interference studies where its suppression reduced COX activity by 49–63% and disrupted complex stability . The subunit interacts with mitochondrial-encoded core subunits (COX I, II, III) and nuclear-encoded regulatory subunits, forming a functional dimer .
Oxygen Sensing and Metabolic Regulation
In mammals, COX4 isoforms (e.g., COX4i1 and COX4i2) modulate oxygen affinity, with COX4i2-containing COX exhibiting lower oxygen affinity (p50 increased 2-fold) under hypoxic conditions . While bacterial ctaF lacks isoforms, its structural homology to mammalian COX4 suggests conserved roles in oxygen-dependent regulation.
Biochemical Studies
Recombinant ctaF is used to:
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Reconstitute COX complexes in vitro: For structural analysis of subunit interactions .
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Study supercomplex formation: With complexes I and III to understand respiratory chain dynamics .
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Investigate ATP/ADP allosteric regulation: Via binding sites in the matrix domain (residues 36–45 and 113–126 in C. glutamicum) .
Disease-Related Research
Defects in COX assembly due to ctaF mutations are linked to mitochondrial disorders like Leigh syndrome and cardiomyopathy . Recombinant ctaF aids in modeling these pathologies in vitro.
Table 1: Functional Impact of COX4 Isoforms (Mammalian Models)
Product Specs
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Target Background
This polypeptide is a component of cytochrome c oxidase; its specific function remains to be elucidated.
KEGG: cdi:DIP1628
Q&A
What experimental protocols achieve optimal expression of recombinant ctaF in prokaryotic systems?
The expression of functional ctaF requires careful optimization of vector design and growth conditions. As demonstrated in Corynebacterium glutamicum systems , successful protocols involve:
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Vector selection: pEKEx2 plasmid with IPTG-inducible tac promoter
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Codon optimization: Match GC content to host organism (typically 52-58% for C. glutamicum)
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Induction parameters: 0.5 mM IPTG at OD₆₀₀ = 0.8 with post-induction growth at 30°C for 12 hr
Critical validation metrics:
| Parameter | Target Value | Measurement Method |
|---|---|---|
| Solubility | >80% | Centrifugation (100,000g, 1hr) |
| Heme incorporation | 0.9-1.1 hemes/subunit | Pyridine hemochrome assay |
| Yield | 15-20 mg/L | Bradford assay with BSA standard |
Subunit integration into functional complexes requires co-expression with ctaD (subunit I) and ctaC (subunit II) . Failure to maintain a 1:1:1 molar ratio results in incomplete assembly .
Which structural validation methods are essential post-purification?
A three-tiered validation approach is recommended:
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Primary structure:
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Secondary structure:
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Circular dichroism (target α-helix content: 58-62%)
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Tertiary structure:
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Limited proteolysis with trypsin (resistance in residues 45-112 indicates proper folding)
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Common pitfalls:
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≥5% free thiol groups indicate oxidative damage (remediate with 2 mM DTT)
What functional assays best characterize recombinant ctaF activity?
A phased validation strategy prevents misinterpretation:
Resolution protocol:
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Perform 2D BN/SDS-PAGE with anti-COX IV western blot
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Compare ΔΨₘ (membrane potential) using TMRM fluorescence (λₑₓ=548nm, λₑₘ=574nm)
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Validate with genetic complementation (threshold: 40% COX IV for full function )
What experimental designs elucidate ctaF's role in supercomplex formation?
The gold-standard approach combines:
A. Genetic manipulation:
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Inducible CRISPRi knockdown (dCas9-KRAB system)
B. Structural analysis:
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Clear-native PAGE (1% digitonin extraction)
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In situ crosslinking with 1% formaldehyde (15min quenching with 125mM glycine)
Key parameters to monitor:
| Supercomplex Form | ctaF Requirement |
|---|---|
| III₂IV₂ | Strict |
| IⅢ₂IV₂ | Partial |
| Free Complex IV | None |
Methodological Innovations
Recent advances from cognitive task analysis frameworks suggest:
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Protocol standardization: 87% reproducibility improvement using decision trees for troubleshooting
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Data contradiction matrices: Resolve 64% of conflicts through systematic factor analysis
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Adaptive sampling: Reduce required experiments by 40% via Gaussian process regression
