Recombinant Macaca mulatta (Rhesus macaque) Cytochrome c oxidase subunit 2 (MT-CO2)

How does the structure of MT-CO2 in Macaca mulatta compare to other primates?

Comparative analysis of MT-CO2 across primates reveals several distinctive structural features:

• Primate MT-CO2 mRNAs contain unique 3'-untranslated regions of 20-25 nucleotides that are absent in non-primate homologues

• Both human and macaque MT-CO2 sequences form stable stem and loop structures preceding duplication sites that may have facilitated evolutionary mutational events

• Certain regions conserved in primates exhibit significantly higher hydrophobicity than their non-primate counterparts

• The amino terminal end of MT-CO2 shows increased variation in higher primates, including rhesus macaques

These structural differences have important functional implications, particularly for the interaction between MT-CO2 and cytochrome c in the respiratory chain.

What are the recommended storage and handling conditions for recombinant MT-CO2?

For optimal stability and functionality of recombinant MT-CO2 from Macaca mulatta:

• Store lyophilized protein at -20°C, and for extended storage, conserve at -20°C or -80°C

• Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL

• Add 5-50% glycerol (final concentration) when aliquoting for long-term storage

• Avoid repeated freeze-thaw cycles as they compromise protein integrity

• Working aliquots may be stored at 4°C for up to one week

The protein is typically supplied in Tris-based buffer with optimized pH (around 8.0) and stabilizers such as glycerol or trehalose.

How has the MT-CO2 gene evolved within the primate lineage?

The evolution of MT-CO2 in primates shows several distinctive patterns:

Phylogenetic analysis of MT-CO2 from 25 primate species supports a sister-group relationship between tarsiers and the monkey/ape clade, and between ring-tail lemurs and gentle lemurs . These evolutionary patterns provide insights into the functional adaptations of the respiratory chain across primate evolution.

What specific amino acid changes in MT-CO2 distinguish rhesus macaques from humans?

Comparison between human and macaque MT-CO2 sequences has revealed several key differences:

• The replacement of two carboxyl-bearing residues (glutamate and aspartate) at positions 114 and 115 in higher primates

• Regions with increased hydrophobicity compared to non-primate counterparts

• Variations in the amino terminal end of the protein

These amino acid substitutions significantly impact protein function, particularly explaining the poor enzyme kinetics observed in cross-reactions between cytochromes c and cytochrome c oxidases when comparing higher primates with other mammals. This has important implications for using rhesus macaque models in research related to human mitochondrial function .

What expression systems are most effective for producing functional recombinant MT-CO2?

While E. coli is commonly used for recombinant protein expression, MT-CO2 presents specific challenges as a membrane-associated mitochondrial protein. The most effective expression systems typically include:

• E. coli systems with specialized vectors: Using vectors designed for membrane proteins with fusion tags (commonly His-tag) to facilitate purification

• Insect cell systems: Baculovirus expression systems provide eukaryotic post-translational modifications

• Mammalian cell expression: For studies requiring native-like folding and modifications

The choice of expression system depends on research objectives - E. coli systems typically yield higher protein quantities but may compromise on post-translational modifications, while eukaryotic systems better preserve native protein structure but with lower yields .

What assays can be used to verify the functional activity of recombinant MT-CO2?

To verify that recombinant MT-CO2 maintains its functional properties:

• Cytochrome c oxidation assays: Measuring the rate of cytochrome c oxidation spectrophotometrically

• Oxygen consumption measurements: Using oxygen electrodes to measure oxygen reduction activity

• Electron transfer kinetics: Analyzing the rate of electron transfer between cytochrome c and MT-CO2

• Binding affinity assays: Quantifying the interaction between MT-CO2 and cytochrome c using techniques such as surface plasmon resonance

• Reconstitution into liposomes: Assessing function in a membrane-like environment

When comparing activity across species, researchers should account for the evolutionary differences that affect enzyme kinetics, particularly the amino acid substitutions at positions 114 and 115 .

How can researchers analyze MT-CO2 interactions with other components of the respiratory chain?

Several methodological approaches can elucidate MT-CO2 interactions:

• Co-immunoprecipitation: Isolating MT-CO2 along with interacting partners

• Blue Native PAGE: Preserving protein-protein interactions for analysis of intact respiratory complexes

• Crosslinking studies: Identifying proximity relationships between MT-CO2 and other proteins

• Förster Resonance Energy Transfer (FRET): Detecting protein interactions in real-time

• Molecular dynamics simulations: Predicting interaction interfaces based on structural data

• Cryo-electron microscopy: Visualizing the structure of MT-CO2 within the cytochrome c oxidase complex

These methods help characterize how MT-CO2 interacts with other subunits of cytochrome c oxidase and with electron donors like cytochrome c, providing insights into the functional consequences of species-specific variations .

How is MT-CO2 utilized in studies of mitochondrial dysfunction?

MT-CO2 serves as a critical component in research on mitochondrial dysfunction:

• Biomarker studies: Changes in MT-CO2 expression or modification can indicate mitochondrial stress

• Respiratory chain analysis: MT-CO2 function directly reflects Complex IV activity, a common site of mitochondrial dysfunction

• Evolutionary medicine: Comparing human and macaque MT-CO2 provides insights into primate-specific aspects of mitochondrial diseases

• Structure-function analysis: Mutations or variations in MT-CO2 can be linked to specific changes in cytochrome c oxidase activity

The rhesus macaque's evolutionary proximity to humans makes its MT-CO2 valuable for modeling human mitochondrial disorders, though the functional differences must be accounted for when interpreting results .

What methodological considerations are important when using MT-CO2 in cross-species comparative studies?

When conducting comparative studies of MT-CO2 across species:

• Accounting for sequence variations: The nearly two-fold increase in amino acid replacement rates in higher primates necessitates careful sequence alignment

• Addressing functional differences: The replacement of carboxyl-bearing residues at positions 114-115 affects enzyme kinetics and must be considered when comparing activity

• Standardizing experimental conditions: pH, temperature, and ionic conditions should be optimized for each species' MT-CO2

• Appropriate control selection: Using phylogenetically informed controls to account for evolutionary distance

• Data normalization: Developing appropriate normalization strategies to account for species-specific differences in MT-CO2 activity

For example, when comparing human and rhesus macaque MT-CO2, researchers should consider the poor enzyme kinetics in cross-reactions between cytochromes c and cytochrome c oxidases from these species due to specific amino acid substitutions .

How can researchers effectively design experiments to study post-translational modifications of MT-CO2?

To investigate post-translational modifications (PTMs) of MT-CO2:

• Mass spectrometry approaches:

  • Tandem MS for identification of specific PTM types and sites

  • Top-down proteomics for analysis of intact protein modifications

  • Quantitative MS to compare modification levels under different conditions

• Site-directed mutagenesis:

  • Mutating potential modification sites to assess functional impact

  • Creating phosphomimetic mutations to simulate permanent phosphorylation

• Modification-specific antibodies:

  • Developing antibodies that recognize specific PTMs on MT-CO2

  • Western blotting and immunoprecipitation to detect modified forms

• In vitro modification assays:

  • Reconstituting modification enzymes with purified MT-CO2

  • Analyzing reaction kinetics and substrate specificity

• Functional correlation studies:

  • Correlating levels of specific PTMs with changes in cytochrome c oxidase activity

  • Examining PTMs in response to cellular stress and metabolic changes

When working with recombinant MT-CO2, researchers should be aware that heterologous expression systems may not reproduce the same pattern of PTMs found in native rhesus macaque mitochondria .

How can MT-CO2 be utilized in studies of respiration and CO2 regulation in rhesus macaques?

MT-CO2 can provide valuable insights into respiration and CO2 regulation:

• Respiratory chain efficiency: MT-CO2 function directly impacts the efficiency of cellular respiration and CO2 production

• Tissue-specific expression patterns: Analyzing MT-CO2 expression across tissues reveals metabolic specialization

• Adaptation to environmental conditions: Examining MT-CO2 function under varying oxygen levels and CO2 concentrations

Research has shown that PCO2 values in rhesus macaques vary by tissue type, with measurements in oviductal fluid showing an average level of about 89 Torr (compared with 40 Torr for blood). During the follicular phase, this corresponds to 35 mM HCO3-, while during the secretory phase, it corresponds to 90 mM HCO3- . Understanding MT-CO2's role in cellular respiration provides context for these physiological measurements.

What role does MT-CO2 play in immune response studies using rhesus macaque models?

While MT-CO2 is not directly involved in immune function, it has significant relevance in immune response studies:

• Metabolic reprogramming during immune activation: Changes in MT-CO2 expression and function reflect shifts in cellular metabolism during immune responses

• Mitochondrial stress in infection models: Viral infections (such as SARS-CoV-2) can impact mitochondrial function and MT-CO2 activity

• Inflammation and oxidative stress: MT-CO2 function is affected by inflammatory conditions and oxidative damage

• Energy metabolism in immune cells: MT-CO2 supports the high energy demands of activated immune cells

Studies with rhesus macaques for COVID-19 vaccine development have incorporated analysis of respiratory parameters and mitochondrial function, where MT-CO2 plays a critical role . For example, research has shown that vaccination with VSV-SARS2-EBOV in rhesus macaques affected genes associated with mitochondrial function, including MT-CO2, suggesting metabolic changes during immune response .

How does the analysis of MT-CO2 contribute to evolutionary studies of primates?

MT-CO2 provides several advantages for evolutionary studies:

• Mitochondrial inheritance: Its mitochondrial encoding makes MT-CO2 valuable for matrilineal evolutionary studies

• Evolutionary rate differentials: The contrast between conserved functional domains and variable regions helps resolve phylogenetic relationships

• Molecular clock applications: MT-CO2 sequence divergence can be used to estimate divergence times between primate species

• Selection pressure analysis: Patterns of synonymous vs. non-synonymous substitutions reveal evolutionary forces acting on respiratory function

Research has used MT-CO2 sequences from 25 primate species to address phylogenetic questions, finding support for specific relationships such as the sister-group relationship between tarsiers and the monkey/ape clade . The Macaca mulatta MT-CO2 sequence is available through resources such as the Ensembl genome browser (assembly Mmul_10, GCA_003339765.3), facilitating comparative genomic studies .

What are common challenges in expressing and purifying functional recombinant MT-CO2?

Researchers frequently encounter these challenges when working with MT-CO2:

The recombinant protein may require specific tags for purification, but these can sometimes interfere with function and may need to be removed. Specialized purification techniques that maintain the native-like environment are often necessary .

How can researchers address the functional differences between recombinant and native MT-CO2?

To ensure recombinant MT-CO2 accurately represents the native protein:

• Functional comparison with isolated mitochondria: Benchmark activity against native cytochrome c oxidase from macaque mitochondria

• Reconstitution into liposomes or nanodiscs: Provide a membrane-like environment that better mimics native conditions

• Co-expression with interacting partners: Express MT-CO2 alongside other cytochrome c oxidase subunits

• Post-purification treatments: Incorporate appropriate lipids and cofactors to restore native-like function

• Structural validation: Use circular dichroism or limited proteolysis to confirm proper folding

The importance of these approaches is underscored by findings that show poor enzyme kinetics in cross-reactions between cytochromes c and cytochrome c oxidases of higher primates and other mammals, highlighting that proper context is crucial for accurate functional assessment .

What controls should be included when designing experiments using recombinant MT-CO2?

Rigorous experimental design for MT-CO2 studies should include:

• Negative controls:

  • Heat-denatured MT-CO2 to establish baseline for activity assays

  • Empty vector preparations to control for host cell contaminants

  • Buffer-only controls to assess assay background

• Positive controls:

  • Commercial cytochrome c oxidase with known activity

  • Fresh mitochondrial preparations as a benchmark for native activity

  • Previously validated MT-CO2 preparations with established activity levels

• Specificity controls:

  • MT-CO2 from related species to assess conservation of function

  • Site-directed mutants affecting key functional residues

  • Inhibitor controls using known cytochrome c oxidase inhibitors

• Process controls:

  • Monitoring protein stability during storage and experimentation

  • Batch consistency checks across preparations

  • Environmental variable controls (pH, temperature, ionic strength)

These controls are particularly important when comparing MT-CO2 from different species, as the evolutionary differences in sequence can significantly impact function and interactions with other components of the respiratory chain .

How might emerging technologies enhance our understanding of MT-CO2 structure and function?

Emerging technologies offer new opportunities for MT-CO2 research:

• Cryo-electron microscopy: Achieving near-atomic resolution of MT-CO2 within the entire cytochrome c oxidase complex

• AlphaFold and similar AI platforms: Predicting species-specific structural variations and their functional impacts

• Single-molecule techniques: Observing conformational changes during the catalytic cycle in real-time

• Gene editing in primate models: Creating precise mutations to study structure-function relationships in vivo

• Multi-omics approaches: Integrating proteomics, metabolomics, and transcriptomics to understand MT-CO2 in cellular context

These technologies can help resolve outstanding questions about the functional consequences of primate-specific amino acid substitutions in MT-CO2, particularly those at positions 114 and 115 that affect interactions with cytochrome c .

What potential applications exist for MT-CO2 in developing mitochondrial therapeutics?

MT-CO2's central role in cellular respiration suggests several therapeutic applications:

• Drug screening platforms: Using recombinant MT-CO2 to identify compounds that enhance cytochrome c oxidase activity

• Biomarker development: Leveraging species-specific differences to develop targeted approaches for mitochondrial disorders

• Evolutionary medicine insights: Understanding how primate-specific adaptations in MT-CO2 affect susceptibility to mitochondrial dysfunction

• Biomimetic catalysts: Designing artificial catalysts based on the efficient oxygen reduction properties of MT-CO2

• Mitochondrial replacement therapies: Informing approaches for treating mitochondrial DNA disorders involving MT-CO2 mutations

The comparative analysis between human and rhesus macaque MT-CO2 can provide valuable insights into the evolutionary adaptation of mitochondrial function and guide the development of species-appropriate interventions for mitochondrial disorders .