Recombinant Hylobates lar ATP synthase subunit a (MT-ATP6)

How does the recombinant Hylobates lar MT-ATP6 protein differ from native protein in terms of structure and functionality?

The recombinant Hylobates lar MT-ATP6 available for research contains the full-length (1-226 amino acids) protein sequence fused to an N-terminal His tag and is expressed in E. coli expression systems . This differs from the native protein in several important ways:

• His-tag addition: The recombinant protein includes an N-terminal histidine tag that facilitates purification but is not present in the native protein

• Post-translational modifications: The E. coli expression system lacks the machinery for mammalian post-translational modifications that may be present in native Hylobates lar MT-ATP6

• Membrane environment: The native protein exists in the lipid-rich environment of the inner mitochondrial membrane, while the recombinant protein is purified and typically provided as a lyophilized powder

Despite these differences, the recombinant protein retains the primary sequence information necessary for structural studies, antibody production, and protein-protein interaction analyses.

What conservation exists between Hylobates lar MT-ATP6 and other primate ATP6 proteins?

Hylobates lar MT-ATP6 shares significant sequence homology with ATP6 proteins from other primates, particularly in regions crucial for protein function. The highest conservation is observed in:

• Proton channel residues: Amino acids that line the proton half-channels, particularly those involved in proton coordination

• Interface regions: Residues that interface with other ATP synthase subunits

• Functional motifs: Conserved sequence motifs involved in proton translocation

This conservation reflects the fundamental importance of ATP synthase function across species. Notably, disease-causing mutations in human MT-ATP6 often occur at residues that are highly conserved across primates, including Hylobates lar .

What are the optimal storage and handling conditions for recombinant Hylobates lar MT-ATP6 protein?

For optimal stability and activity of recombinant Hylobates lar MT-ATP6 protein, researchers should adhere to the following storage and handling guidelines:

• Storage temperature: Store at -20°C/-80°C upon receipt; aliquoting is necessary for multiple use

• Reconstitution protocol:

  • Briefly centrifuge the vial prior to opening

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

  • Add 5-50% glycerol (final concentration) and aliquot for long-term storage at -20°C/-80°C

• Freeze-thaw considerations: Repeated freezing and thawing is not recommended

• Working storage: Store working aliquots at 4°C for up to one week

• Buffer compatibility: The protein is provided in Tris/PBS-based buffer with 6% Trehalose, pH 8.0

Adhering to these conditions helps maintain protein integrity and prevents degradation that could compromise experimental results.

What protocols are recommended for reconstituting Hylobates lar MT-ATP6 into liposomes for functional studies?

For functional studies of recombinant Hylobates lar MT-ATP6, researchers can adapt protocols similar to those used for other ATP synthase complexes. Based on methodologies for ATP synthase reconstitution:

• Liposome preparation:

  • Use a mixture of phospholipids (typically phosphatidylcholine and phosphatidic acid at 9:1 ratio)

  • Dissolve lipids in chloroform, evaporate solvent under nitrogen, and rehydrate

  • Subject to freeze-thaw cycles and extrusion through polycarbonate filters

• Protein incorporation:

  • Solubilize the protein in a detergent (e.g., n-dodecyl β-D-maltoside)

  • Mix with preformed liposomes at protein-to-lipid ratios of 1:50 to 1:100

  • Remove detergent via Bio-Beads or dialysis

• Verification of incorporation:

  • Assess protein orientation using protease protection assays

  • Confirm incorporation using density gradient centrifugation

When properly reconstituted, ATP synthase proteoliposomes should be capable of ATP synthesis when energized with appropriate ion gradients (Na+ or H+) .

How can researchers assess the functional activity of recombinant Hylobates lar MT-ATP6?

Assessing the functional activity of recombinant Hylobates lar MT-ATP6 requires either working with the purified reconstituted ATP synthase complex or using the protein in reconstitution experiments with other ATP synthase components. Key approaches include:

• ATP synthesis assays: Measure ATP synthesis in reconstituted proteoliposomes energized by artificial ion gradients

  • Create a potassium diffusion potential using valinomycin (typically 120-160 mV)

  • Establish ion gradients (ΔpNa or ΔpH) across the membrane

  • Add ADP and monitor ATP production using luciferase-based assays

• ATP hydrolysis assays: Measure the reverse reaction (ATP hydrolysis)

  • Typical activities for functional ATP synthase in proteoliposomes range from 0.5-1.0 U/mg

  • Use enzyme-coupled assays that link ATP hydrolysis to NADH oxidation

• Ion coupling specificity: Determine whether the enzyme is coupled to Na+ or H+ by:

  • Varying ion concentrations while keeping electrical potential constant

  • Using specific ionophores (e.g., ETH2120 for Na+, TCS for H+)

  • Testing inhibitor sensitivity (e.g., DCCD which competes with ions for binding)

Table: Theoretical driving force requirements based on ATP synthase functional studies

How does the structure of MT-ATP6 contribute to the proton channel function in ATP synthase?

The MT-ATP6 subunit forms a critical part of the proton translocation pathway in ATP synthase, with several key structural features:

• Transmembrane helices: MT-ATP6 contains multiple transmembrane helices that contribute to forming the proton half-channels on both the matrix and cristae lumen sides

• Proton half-channels:

  • The lumenal proton half-channel conducts protons from the intermembrane space

  • This channel contains ordered water molecules coordinated by conserved residues

  • A conserved arginine residue (equivalent to R146 in other species) acts as a critical element separating the half-channels

• Interaction with c-ring:

  • MT-ATP6 positions conserved charged residues adjacent to the c-ring

  • These residues facilitate proton transfer to glutamate residues on the c-ring subunits (equivalent to E102 in some species)

  • The sequential protonation of c-ring glutamates drives rotation of the c-ring

• Lipid interactions:

  • Specific lipids may occupy positions in the proton path

  • In some species, a phosphatidylcholine molecule replaces protein elements in lining the proton path

This structure enables the coordinated transfer of protons that ultimately drives the rotation of the c-ring and ATP synthesis.

What role does MT-ATP6 play in the dimerization and oligomerization of ATP synthase complexes?

MT-ATP6 contributes to ATP synthase dimerization and oligomerization, which are critical for creating the distinctive curvature of the inner mitochondrial membrane:

• Dimer interface contribution:

  • The transmembrane region of MT-ATP6 contributes to the dimer interface

  • In some organisms, specific lipids at this interface mediate interactions between monomers

  • The buried surface area at this interface varies considerably across species (from approximately 3,600 Ų to 16,000 Ų)

• Organization of oligomeric rows:

  • MT-ATP6 positioning influences the angle between monomers in a dimer

  • This angle determines how dimers arrange into the larger oligomeric assemblies that shape cristae

  • The specific arrangement varies among species; some form parallel rows while others form more complex structures

• Evolutionary conservation:

  • The dimerization interfaces show considerable diversity across evolutionary lineages

  • Some elements appear to be conserved across species, suggesting a common ancestral interaction module

  • Other elements are lineage-specific, representing independent evolutionary adaptations

The structural variations in MT-ATP6 across species contribute to the different architectures of ATP synthase dimers and oligomers observed in various organisms.

What are the known functional consequences of mutations in MT-ATP6?

Mutations in MT-ATP6 have significant functional consequences for ATP synthase activity and are associated with several mitochondrial diseases:

• Effects on proton translocation:

  • Mutations can disrupt the proton channel structure

  • This impairs proton flow through the half-channels

  • Reduced proton translocation decreases the efficiency of ATP synthesis

• Impaired catalytic activity:

  • Some mutations reduce the coupling between proton movement and ATP synthesis

  • This results in decreased ATP production even when proton gradients are present

  • Energy is dissipated as heat rather than captured as ATP

• Disease-associated variants:

  • The m.8993T>G mutation is a well-characterized pathogenic variant

  • This mutation substitutes a highly conserved leucine with arginine in the proton channel

  • It is associated with neurogenic muscle weakness, ataxia, and retinitis pigmentosa (NARP) and Leigh syndrome

• Bioenergetic consequences:

  • Reduced ATP synthesis capacity

  • Increased production of reactive oxygen species

  • Mitochondrial membrane potential changes

  • Compromised cellular energy homeostasis

These functional consequences highlight the critical role of MT-ATP6 in cellular energy production and explain why mutations in this gene often manifest as disorders with high energy demand tissues such as brain and muscle.

How can Hylobates lar MT-ATP6 be used as a model for studying evolutionary adaptations in mitochondrial genes?

Hylobates lar MT-ATP6 provides an excellent model for evolutionary studies of mitochondrial genes for several reasons:

• Phylogenetic positioning:

  • Gibbons (Hylobates) occupy an intermediate position in primate evolution

  • Comparison with human, great ape, and other primate MT-ATP6 sequences can reveal adaptive changes

  • The evolutionary rate of change in MT-ATP6 can be assessed across different primate lineages

• Sequence-function relationships:

  • The identification of conserved vs. variable regions in Hylobates lar MT-ATP6 compared to other primates

  • Correlation of these variations with specific functional adaptations

  • Analysis of selection pressures on different regions of the protein

• Co-evolution with nuclear genes:

  • Study how MT-ATP6 co-evolves with nuclear-encoded ATP synthase subunits

  • Investigate mechanisms of mitonuclear compatibility

  • Examine how compensatory mutations maintain ATP synthase function across evolutionary time

• Adaptation to environmental factors:

  • Investigate whether MT-ATP6 variations correlate with ecological factors (altitude, temperature, diet)

  • Assess whether specific variations provide selective advantages under different environmental conditions

  • Compare with other species that have adapted to similar environments

The recombinant protein provides a tool for experimental testing of hypotheses derived from sequence analysis, allowing researchers to connect genotypic changes with phenotypic consequences.

What are the current challenges in studying low driving force ATP synthesis with recombinant ATP synthase systems?

Studying ATP synthesis at low driving forces presents several methodological challenges that researchers need to address:

• Reconstitution challenges:

  • Achieving proper orientation of ATP synthase in liposomes

  • Maintaining protein stability during reconstitution

  • Ensuring tight coupling between proton movement and ATP synthesis

• Measurement sensitivity:

  • At low driving forces (87-90 mV), ATP synthesis rates are considerably lower

  • Highly sensitive detection methods are required

  • Background ATP contamination must be rigorously controlled

• Driving force generation and maintenance:

  • Precisely establishing defined membrane potentials (Δψ)

  • Creating stable ion gradients (ΔpNa or ΔpH)

  • Preventing gradient dissipation during experiments

• Distinguishing driving force components:

  • Separating the contributions of Δψ vs. ΔpNa/ΔpH

  • Determining threshold values for each component

  • Understanding their synergistic effects

Table: Comparison of driving force requirements for different ATP synthase types

How can researchers investigate the ion specificity of Hylobates lar MT-ATP6?

The ion specificity of Hylobates lar MT-ATP6 can be investigated through several complementary approaches:

• Mutagenesis of key residues:

  • Identify and mutate putative ion-coordinating residues

  • Assess the impact on ATP synthesis and hydrolysis activities

  • Examine changes in ion dependence of enzymatic activities

• Ion competition studies:

  • Vary the concentrations of different ions (Na⁺, H⁺, K⁺, etc.)

  • Determine EC₅₀ values for each ion

  • Assess competitive inhibition patterns

• Inhibitor sensitivity profiling:

  • Use DCCD (N,N'-dicyclohexylcarbodiimide) which competes with ions for binding to c-ring

  • Test whether Na⁺ or H⁺ can protect against DCCD inhibition

  • Compare inhibition constants with those of known Na⁺- or H⁺-dependent ATP synthases

• Direct ion binding measurements:

  • Use isothermal titration calorimetry to measure ion binding

  • Apply fluorescent probes sensitive to specific ions

  • Employ Na⁺ or H⁺ NMR to detect binding events

• Bioenergetic assessments:

  • Generate specific ion gradients across liposomal membranes

  • Determine which gradients can drive ATP synthesis

  • Measure the ATP synthesis rates as a function of different ion gradients

These methodologies can establish whether Hylobates lar MT-ATP6 functions primarily as a Na⁺- or H⁺-coupled enzyme, or whether it possesses the ability to utilize both ions under different conditions.

How can Hylobates lar MT-ATP6 be used as a comparative model for studying human MT-ATP6 disease variants?

Hylobates lar MT-ATP6 provides a valuable comparative model for studying human disease-associated variants through several approaches:

• Conserved pathogenic sites:

  • Identify whether sites of human pathogenic mutations (such as m.8993T>G) are conserved in Hylobates lar

  • Create equivalent mutations in the recombinant Hylobates protein

  • Compare functional consequences with those observed in human variants

• Species-specific tolerance:

  • Determine whether certain mutations have different effects in Hylobates versus human MT-ATP6

  • Identify compensatory mechanisms that might exist in gibbon ATP synthase

  • Investigate the structural basis for differential sensitivity to mutations

• Hybrid systems analysis:

  • Create chimeric ATP synthase complexes with components from both human and Hylobates systems

  • Test whether gibbon components can rescue function of human disease variants

  • Identify which domains or residues confer resistance to pathogenic effects

• Evolutionary context:

  • Examine the evolutionary history of disease-associated sites

  • Determine whether certain lineages show evidence of positive selection at these sites

  • Investigate whether natural variations present in primates could inform therapeutic approaches for human diseases

This comparative approach can provide insights into the mechanistic basis of MT-ATP6-associated diseases and potentially identify novel therapeutic strategies.

What methodologies are recommended for assessing the impact of point mutations in recombinant MT-ATP6?

Comprehensive assessment of MT-ATP6 point mutations requires a multi-faceted methodological approach:

• Site-directed mutagenesis:

  • Generate specific point mutations in recombinant MT-ATP6

  • Confirm mutations by sequencing

  • Express and purify mutant proteins using the same protocols as wild-type

• Structural integrity assessment:

  • Circular dichroism spectroscopy to assess secondary structure

  • Limited proteolysis to evaluate conformational changes

  • Thermal stability assays to determine whether mutations affect protein stability

• Functional assays:

  • ATP synthesis measurements in reconstituted systems

  • ATP hydrolysis activity determination

  • Ion binding and translocation assessments

  • Proton/sodium pumping assays using pH/Na⁺-sensitive fluorescent dyes

• Integration into ATP synthase complex:

  • Co-reconstitution with other ATP synthase subunits

  • Blue native PAGE to assess complex assembly

  • Immunoprecipitation to evaluate subunit interactions

• Quantitative comparisons:

  • Determine kinetic parameters (Km, Vmax) for wild-type and mutant proteins

  • Calculate coupling efficiency (ratio of ATP synthesis to ion translocation)

  • Measure threshold potential required for ATP synthesis

These methods provide complementary information about how mutations affect different aspects of MT-ATP6 function, from protein folding to its role in the complete ATP synthase complex.

What are the emerging techniques for studying the dynamic behavior of MT-ATP6 within the ATP synthase complex?

Several cutting-edge techniques are expanding our ability to study the dynamic behavior of MT-ATP6:

• Time-resolved cryo-electron microscopy:

  • Capture different conformational states during the catalytic cycle

  • Visualize rotary motion and associated structural changes

  • Identify transient interactions between MT-ATP6 and the c-ring

• Single-molecule fluorescence resonance energy transfer (smFRET):

  • Track real-time conformational changes during ATP synthesis/hydrolysis

  • Measure rotational steps of the c-ring relative to MT-ATP6

  • Determine kinetics of individual steps in the catalytic cycle

• Molecular dynamics simulations:

  • Model proton movement through the half-channels

  • Simulate interactions between MT-ATP6 and lipids in the membrane

  • Predict effects of mutations on structure and function

• In situ cryo-electron tomography:

  • Study ATP synthase organization within native membrane environments

  • Visualize oligomerization and membrane curvature

  • Examine interactions with other mitochondrial complexes

• Mass photometry:

  • Analyze subunit stoichiometry and complex assembly in solution

  • Monitor binding of small molecules and lipids

  • Assess effects of mutations on complex stability

These emerging techniques promise to provide unprecedented insights into the dynamic behavior of MT-ATP6 within the functioning ATP synthase complex.

How might synthetic biology approaches incorporate Hylobates lar MT-ATP6 for novel energy-harvesting systems?

Synthetic biology offers innovative ways to utilize Hylobates lar MT-ATP6 in engineered energy-harvesting systems:

• Hybrid ATP synthase engineering:

  • Create chimeric ATP synthases combining attributes from different species

  • Engineer ATP synthases with enhanced efficiency at low driving forces

  • Incorporate MT-ATP6 variants optimized for specific ion gradients

• Artificial energy-harvesting vesicles:

  • Reconstitute engineered ATP synthases into synthetic vesicles

  • Couple with light-driven proton pumps for solar energy capture

  • Design self-sustaining ATP-generating systems

• Adaptation to non-physiological energy sources:

  • Engineer MT-ATP6 to respond to alternative ion gradients (K⁺, Li⁺)

  • Modify ion specificity through targeted mutations

  • Create systems that can function in non-biological environments

• Nanoscale power generators:

  • Immobilize engineered ATP synthases on artificial surfaces

  • Harvest energy from environmental pH gradients

  • Develop ATP-generating components for nanomachines

• Biosensor applications:

  • Utilize MT-ATP6 sensitivity to membrane potential

  • Develop sensors for detecting ion gradients or electrical potentials

  • Create diagnostic tools based on ATP synthase activity

These synthetic biology approaches could lead to novel bioenergetic technologies with applications in biofuel production, nanomedicine, and environmental sensing.