PET191 Antibody

What is PET191 and why is it significant in mitochondrial research?

PET191 (also known as COA5 in humans) is an essential cytochrome c oxidase (CcO) assembly factor that contains twin-Cx9C motifs. It is critical for the maturation of cytochrome c oxidase (respiratory chain complex IV). PET191 is tightly associated with the mitochondrial inner membrane facing the intermembrane space (IMS) . Its significance stems from its fundamental role in mitochondrial respiratory function, as it participates in the early steps of complex IV assembly. Mutations in the human PET191 gene (C2orf64) have been linked to CcO deficiency and fatal hypertrophic cardiomyopathy, underscoring its importance in mitochondrial function and human health .

What are the structural characteristics of PET191 protein?

PET191 contains six conserved cysteine residues, with at least two (Cys5 and Cys56) being critical for its function through participation in disulfide bond formation. The protein adopts a structure reminiscent of a helical hairpin, similar to other twin-Cx9C proteins. Human PET191 has 74 amino acid residues and a molecular mass of approximately 8.4 kDa . PET191 exists in vivo as part of a large oligomeric complex (approximately 500-530 kDa) that is sensitive to reducing agents, suggesting that disulfide bonds play a crucial role in maintaining its quaternary structure . When isolated from mitochondria under non-reducing conditions, PET191 maintains these complex associations, but treatment with reducing agents like DTT causes it to migrate at a volume corresponding to its monomeric mass during gel filtration .

How does PET191 function differ between yeast and human cells?

In both yeast and human cells, PET191 is essential for cytochrome c oxidase assembly. In yeast (S. cerevisiae), pet191Δ mutant strains show deficient complex IV activity while activities of other respiratory complexes like succinate:cytochrome c oxidoreductase (complex II+III) are elevated . These mutants retain normal mitochondrial translation but show reduced levels of Cox1p, Cox2p, and Cox3p proteins.

In human cells, PET191 knockout leads to undetectable levels of COX2 and holo-CIV, pointing to its crucial role in complex IV assembly . Human PET191 mutations can cause CcO deficiency and fatal hypertrophic cardiomyopathy. Interestingly, while the basic function is conserved, human PET191 contains additional functional cysteine residues (C30 and C41) that appear to play roles in copper or redox transfer that are important for its function in restoring CcO activity in COX11-deficient cells .

What are the recommended applications for PET191 antibodies in mitochondrial research?

PET191 antibodies are valuable tools in several experimental applications:

• Western Blotting: For detecting PET191 protein levels in mitochondrial fractions and assessing changes in expression under different experimental conditions .

• ELISA: For quantitative measurement of PET191 levels in biological samples .

• Immunoprecipitation: To study protein-protein interactions, as demonstrated by co-immunoprecipitation studies showing PET191 homo-oligomerization .

• BN-PAGE (Blue Native Polyacrylamide Gel Electrophoresis): To analyze the complex formation and oligomeric state of PET191 .

• Subcellular localization studies: To confirm mitochondrial localization and membrane association through fractionation followed by immunoblotting .

For optimal results, use antibodies specifically validated for the experimental model system (yeast, human, etc.) and application of interest.

How should researchers design experiments to study PET191 complex formation?

When studying PET191 complex formation, consider the following methodological approach:

• Choice of detergent: Digitonin and deoxycholate (DOC) have been successfully used to solubilize PET191 while maintaining its native complex structure. Digitonin is preferred for BN-PAGE analysis, while 0.1% DOC works well for size permeation chromatography .

• Redox considerations: Include both reducing and non-reducing conditions in your experimental design. Under non-reducing conditions, PET191 exists in a complex of approximately 500-530 kDa, while addition of 100 mM DTT results in a shift to its monomeric mass .

• Tagged protein versions: Using epitope-tagged versions (e.g., PET191-HA, PET191-Myc) facilitates detection in complex samples. These tags have been shown not to interfere with function when properly positioned .

• Controls for specificity: Include appropriate controls such as knockout/knockdown cells, non-specific antibodies, and blocking peptides to ensure signal specificity.

• Analysis techniques: Combine BN-PAGE with size exclusion chromatography to comprehensively characterize the complex. For BN-PAGE, load solubilized mitochondrial extracts (50-100 μg protein) on 4-16% gradient gels. For size permeation chromatography, apply DOC-solubilized extracts to a Superose 6 column .

How can researchers effectively analyze the redox state of PET191 and its impact on interaction partners?

To effectively analyze the redox state of PET191 and its impact on interaction partners:

• Sequential thiol trapping: Apply techniques that differentiate between oxidized and reduced cysteine residues. This involves treating samples with N-ethylmaleimide (NEM) to block reduced thiols, followed by DTT reduction and labeling of previously oxidized thiols with a different alkylating agent.

• Diagonal redox SDS-PAGE: This two-dimensional technique allows visualization of disulfide-bonded proteins and can help identify interaction partners linked by disulfide bonds.

• Site-directed mutagenesis: Create systematic mutations of each cysteine residue (particularly C5, C15, C32, C46, and C56 in the twin-Cx9C motifs, plus C30 and C41) to assess their impact on PET191 function and complex formation. The research demonstrates that C5A and C56A mutations lead to respiratory deficiency, while C15A, C32A, and C46A showed partial compromise in function .

• Assess effects on other metallochaperones: Monitor the redox state of interaction partners like COX11, SCO1, and SCO2 when PET191 is mutated or absent. Research shows that loss of PET191 affects the redox state of these proteins, with all becoming more reduced .

• Dominant negative approach: Express mutant forms of PET191 (e.g., C5A, C56A, or C30A/C41A) in wild-type cells to assess interference with endogenous protein function. This has been shown to affect the assembly of native PET191 complexes and impact CcO activity .

What methodological approaches should be used when investigating PET191's role in coordinating copper transfer in cytochrome c oxidase assembly?

When investigating PET191's role in copper transfer during cytochrome c oxidase assembly:

• Genetic suppression analysis: Overexpress PET191 in cells deficient for other copper chaperones (e.g., COX11-KO) to determine functional relationships. Research has shown that PET191 overexpression can partially rescue CcO deficiency in COX11-knockout cells, enhancing CcO activity from 15% to 40% of wild-type levels .

• Co-overexpression studies: Test combinations of different chaperones (e.g., PET191 with COX17) to identify synergistic effects. The simultaneous overexpression of PET191 and COX17 increased CcO activity to 50% in COX11-KO cells .

• Copper supplementation experiments: Evaluate the effect of exogenous copper on the suppression capacity of PET191. Research indicates that additional copper did not further enhance the suppressive effect of PET191 overexpression in COX11-deficient cells .

• Spectroscopic analysis: Perform detailed cytochrome spectra analysis to assess the integrity of heme centers. PET191 overexpression in COX11-KO cells modified the a+a3 cytochrome spectra, with a fraction of the α peak red-shifted (~600 nm vs. 597 nm), suggesting partial restoration of the native state of the binuclear center .

• Interaction studies: Use immunoprecipitation and proximity labeling approaches to identify dynamic interactions between PET191 and other assembly factors in the copper delivery pathway.

How does studying PET191 contribute to our understanding of mitochondrial disorders?

Studying PET191 provides crucial insights into mitochondrial disorders through several mechanisms:

• Genetic basis of CcO deficiency: Mutations in the human PET191 gene (C2orf64) have been linked to cytochrome c oxidase deficiency and fatal hypertrophic cardiomyopathy . Understanding the function of PET191 helps elucidate the molecular pathogenesis of these conditions.

• Assembly factor networks: PET191 functions within a complex network of assembly factors that coordinate the biogenesis of cytochrome c oxidase. Characterizing these networks helps identify potential therapeutic targets and diagnostic markers for mitochondrial disorders.

• Redox homeostasis: PET191 affects the redox state of other metallochaperones like COX11, SCO1, and SCO2 . This suggests a broader role in maintaining redox homeostasis within the mitochondrial intermembrane space, disruption of which may contribute to pathology.

• Coordination of metal center biogenesis: PET191 plays a role in coordinating copper transfer during CcO assembly, highlighting the importance of proper metal center formation in preventing mitochondrial dysfunction .

• Potential compensatory mechanisms: The finding that PET191 overexpression can partially rescue CcO deficiency in COX11-deficient cells suggests potential compensatory mechanisms that could be therapeutically exploited .

Future research should focus on developing animal models of PET191 deficiency, identifying additional interaction partners, and exploring potential therapeutic approaches to address CcO assembly defects.

What are the key methodological challenges in generating and characterizing PET191 knockout cell lines?

Generating and characterizing PET191 knockout cell lines presents several methodological challenges:

• Gene editing efficiency: As demonstrated in the search results, researchers have used both TALEN and CRISPR-Cas9 approaches to generate PET191 knockout cell lines. The TALEN approach required four consecutive transfections every 3 days to achieve sufficient editing, highlighting potential efficiency issues .

• Clone selection strategy: After transfection, cells need to be sorted as single cells in 96-well plates, and clones must be screened by both immunoblotting and genotyping to confirm successful knockout. This process is labor-intensive and time-consuming .

• Verification of complete knockout: Complete ablation of PET191 expression must be verified at both the genomic level (by sequencing the target locus) and the protein level (by immunoblotting with specific antibodies) .

• Phenotypic characterization: PET191 knockout cells show severe respiratory defects, which can impact cell growth and viability. This creates challenges for expanding cultures and maintaining consistent experimental conditions.

• Functional rescue experiments: For proper characterization, complementation with wild-type and mutant PET191 constructs is essential. This requires additional transfection and selection steps, as well as careful control of expression levels .

To address these challenges, researchers should:

• Optimize transfection conditions specific to their cell type

• Use multiple guide RNAs or TALEN pairs to increase editing efficiency

• Implement robust screening strategies combining genomic analysis and protein detection

• Consider inducible knockout systems to minimize selective pressure during cell line generation

• Include appropriate controls for rescue experiments, including expression-matched wild-type and mutant constructs

What are the optimal conditions for immunodetection of PET191 in subcellular fractionation experiments?

For optimal immunodetection of PET191 in subcellular fractionation experiments:

• Fractionation protocol:

  • Isolate mitochondria using differential centrifugation (e.g., 12,000×g for 15 minutes)

  • For submitochondrial fractionation, perform controlled osmotic swelling to generate mitoplasts, followed by proteinase K treatment to distinguish proteins exposed to the intermembrane space

  • Use sodium carbonate extraction at different pH levels (10.5 and 11.5) to differentiate between integral membrane proteins and membrane-associated proteins

• Sample preparation:

  • Include appropriate protease inhibitors throughout the fractionation process

  • Maintain samples at 4°C during preparation to prevent degradation

  • For membrane-associated proteins like PET191, use 0.1% digitonin or 0.1% deoxycholate for solubilization

• Western blot conditions:

  • Load appropriate protein amounts (typically 20-50 μg per lane)

  • Use 12-15% SDS-PAGE gels or gradient gels (4-20%) to effectively resolve the 8.4 kDa PET191 protein

  • Include 0.05% SDS in transfer buffer to enhance transfer of hydrophobic proteins

  • Use PVDF membrane rather than nitrocellulose for better retention of low molecular weight proteins

• Controls:

  • Include markers for different mitochondrial compartments: outer membrane (e.g., Tom20), intermembrane space (e.g., Cyb2), inner membrane (e.g., Cox2), and matrix (e.g., Hsp60)

  • Include PET191 knockout samples as negative controls

  • For tagged versions, include untagged controls to verify specificity

• Antibody conditions:

  • Optimize primary antibody dilution (typically start with 1:1000)

  • Incubate overnight at 4°C for maximum sensitivity

  • Use 5% non-fat dry milk or BSA in TBST for blocking and antibody dilution

How can researchers differentiate between monomeric and oligomeric forms of PET191 in experimental analyses?

To differentiate between monomeric and oligomeric forms of PET191:

• Blue Native PAGE (BN-PAGE):

  • Solubilize mitochondria in 1% digitonin

  • Run samples on 4-16% or 3-12% gradient gels

  • Oligomeric PET191 migrates as a complex of approximately 500 kDa

  • Include both reducing and non-reducing conditions to compare complex stability

  • For comparison, run a parallel strip in the second dimension on SDS-PAGE

• Size Exclusion Chromatography:

  • Solubilize PET191 in 0.1% deoxycholate (DOC)

  • Apply samples to a Superose 6 or similar column

  • Under non-reducing conditions, PET191 elutes at a volume corresponding to ~530 kDa

  • Under reducing conditions (e.g., with 100 mM DTT), PET191 elutes at its monomeric mass

  • Collect fractions and analyze by Western blot

• Crosslinking approaches:

  • Treat intact mitochondria or purified complexes with membrane-permeable crosslinkers

  • Use graduated concentrations of crosslinker to capture various interaction states

  • Analyze by SDS-PAGE and immunoblotting to identify discrete oligomeric species

• Comparative analysis of mutants:

  • Include samples expressing PET191 cysteine mutants (particularly C5A)

  • The C5A mutant protein exists in a smaller complex compared to wild-type

  • Comparative analysis can reveal which residues are crucial for oligomerization

• Analytical ultracentrifugation:

  • For purified protein preparations, use sedimentation velocity or equilibrium experiments

  • This provides precise determination of molecular mass and oligomeric state

  • Compare results under varying redox conditions to assess the role of disulfide bonds