Recombinant Spermophilus tridecemlineatus ATP synthase subunit a (MT-ATP6)

What is MT-ATP6 and what is its normal function in cellular metabolism?

MT-ATP6 encodes the ATP synthase subunit a protein, which forms an essential component of the ATP synthase complex (Complex V) in mitochondria. This protein plays a critical role in oxidative phosphorylation, the process by which cells generate energy. Specifically, MT-ATP6 forms part of the membrane domain that allows protons to flow across the specialized inner mitochondrial membrane. The energy created by this proton flow is then utilized by another segment of the enzyme to convert adenosine diphosphate (ADP) to adenosine triphosphate (ATP), the cell's primary energy source .

What is the amino acid sequence of Recombinant Spermophilus tridecemlineatus ATP synthase subunit a?

The full amino acid sequence (226 amino acids) of Recombinant Spermophilus tridecemlineatus ATP synthase subunit a (MT-ATP6) is:

MNENLFASFITPTLMGLPIVLLIIMFPNLLFPSPTRLMNNRLVSFQQWLIQLVLKQMMAMHNPKGRTWSLMLISLIMFIGSTNLLGLLPHSFTPTTQLSMNLGMAIPLWAGAVITGFRHKTKASLAHFLPQGTPIPLIPMLIIIETISLFIQPMALAVRLTANITAGHLLMHLIGGATLVLTSISPPTAILTFIILVLLTMLEFAVALIQAYVFTLLVSLYLHDNT

How is the recombinant Spermophilus tridecemlineatus MT-ATP6 protein typically produced for research applications?

The recombinant protein is typically expressed in Escherichia coli (E. coli) expression systems. The full-length protein (amino acids 1-226) is often fused with an N-terminal histidine tag (His-tag) to facilitate purification. After expression, the protein is purified and typically prepared as a lyophilized powder. The production process is optimized to ensure protein stability and functionality. For storage and distribution, the protein is prepared in a Tris/PBS-based buffer with 6% Trehalose at pH 8.0, though the exact tag type may be determined during the production process depending on specific research requirements .

What are the recommended storage and handling conditions for recombinant MT-ATP6 protein?

The recombinant protein should be stored at -20°C or -80°C upon receipt, with aliquoting necessary for multiple uses. For extended storage, conservation at -20°C or -80°C is recommended. The protein is typically supplied in a storage buffer containing Tris-based buffer with 50% glycerol, optimized for this specific protein. Working aliquots can be stored at 4°C for up to one week, but repeated freeze-thaw cycles should be avoided as they can degrade protein quality. Prior to opening, vials should be briefly centrifuged to bring contents to the bottom .

What reconstitution protocol is recommended for lyophilized MT-ATP6 protein?

The recommended reconstitution protocol involves dissolving the lyophilized protein in deionized sterile water to achieve a concentration of 0.1-1.0 mg/mL. For long-term storage of the reconstituted protein, it is advised to add glycerol to a final concentration of 5-50% (with 50% being the default recommendation) and then aliquot before storing at -20°C/-80°C. This approach helps maintain protein stability and prevents degradation during storage .

How do mutations in MT-ATP6 affect ATP synthase function and what models are used to study them?

Mutations in the MT-ATP6 gene can significantly impair ATP synthase function by disrupting proton movement across the mitochondrial inner membrane or by affecting the assembly of the ATP synthase complex. These disruptions lead to deficits in ATP production and impaired oxidative phosphorylation.

Saccharomyces cerevisiae (baker's yeast) serves as an excellent model system for investigating the functional consequences of MT-ATP6 mutations due to:

• Its amenability to mitochondrial genetic transformation

• Inability to stably maintain heteroplasmy (mixture of mutant and wild-type mtDNA)

• Strong evolutionary conservation of mitochondrially-encoded proteins

Research has demonstrated that mutations responsible for severe clinical phenotypes dramatically affect the yeast ATP synthase, while those associated with milder diseases compromise oxidative phosphorylation less severely, validating yeast as an effective model system .

What specific mutations in MT-ATP6 have been identified as pathogenic, and how do they correlate with clinical phenotypes?

Several MT-ATP6 mutations have been identified and studied for their pathogenicity:

The T8993G mutation, particularly common in Leigh syndrome cases, has been found in approximately 10% of affected individuals. This syndrome is a progressive brain disorder usually appearing in infancy or early childhood, characterized by delayed development, muscle weakness, movement problems, and breathing difficulties .

What experimental approaches are used to assess the functional impact of MT-ATP6 variants in model systems?

Researchers utilize several experimental approaches to evaluate the functional consequences of MT-ATP6 variants:

• Mitochondrial Genetic Transformation: Introduction of specific mutations into the yeast mitochondrial genome through techniques like biolistic transformation.

• Respiratory Growth Assessment: Evaluation of growth capability on media requiring respiratory metabolism (non-fermentable carbon sources), which directly correlates with mitochondrial function.

• ATP Production Measurement: Quantification of ATP synthesis rates in isolated mitochondria to directly assess the impact on energy production.

• Recombination Studies: Using mtDNA recombination in yeast to integrate variant MT-ATP6 genes into complete mitochondrial genomes (ρ+), allowing for homoplasmy in approximately twelve mitotic divisions.

• Proton Movement Analysis: Examination of proton movements within the hydrophilic cleft of the ATP synthase membrane domain to understand mechanistic disruptions caused by mutations .

How does the evolutionary conservation of ATP synthase subunit a across species facilitate comparative studies of MT-ATP6 function?

The strong evolutionary conservation of ATP synthase subunit a across species makes comparative studies particularly valuable for understanding MT-ATP6 function and the impact of mutations. For example, when studying human MT-ATP6 variants in Saccharomyces cerevisiae, researchers can map the corresponding residues between species.

The mapping of human mutations to yeast equivalents demonstrates this conservation:

• Human p.I106T (m.8843T>C) corresponds to yeast aI123T

• Human p.V142I (m.8950G>A) corresponds to yeast aV159I

• Human p.I164V (m.9016A>G) corresponds to yeast aI181V

• Human p.G167S (m.9025G>A) corresponds to yeast aG184S

• Human p.H168R (m.9029A>G) corresponds to yeast aH185R

• Human p.T178A (m.9058A>G) corresponds to yeast aT195A

• Human p.A205T (m.9139G>A) corresponds to yeast aA225T

• Human p.Y212H (m.9160T>C) corresponds to yeast aY232H

What is the relationship between MT-ATP6 mutations, ATP production deficits, and tissue-specific pathology in mitochondrial disorders?

MT-ATP6 mutations that impair ATP synthase function lead to decreased ATP production and compromised oxidative phosphorylation. While the exact mechanisms linking these deficits to tissue-specific pathology remain under investigation, several key relationships have been established:

• Energy Demand and Sensitivity: Tissues with high energy requirements—particularly the brain, muscles, and heart—show increased sensitivity to decreases in cellular energy availability.

• Cell Death Mechanism: Impaired oxidative phosphorylation likely leads to cell death due to insufficient energy availability within affected cells.

• Severity Correlation: The degree of ATP production deficit correlates with clinical severity—mutations causing severe clinical phenotypes dramatically affect ATP synthase function, while those associated with milder diseases compromise oxidative phosphorylation less severely.

• Heteroplasmy Effects: The percentage of mutated mitochondrial DNA (heteroplasmy) in affected tissues influences disease manifestation and severity.

• Tissue-Specific Thresholds: Different tissues appear to have unique thresholds for mitochondrial dysfunction before exhibiting pathological changes, explaining the variable presentation of symptoms across organ systems .

What are the recommended protocols for reconstituting and working with recombinant MT-ATP6 protein in experimental settings?

For optimal experimental outcomes when working with recombinant MT-ATP6 protein:

• Initial Preparation: Briefly centrifuge the vial prior to opening to ensure all content is at the bottom.

• Reconstitution: Dissolve the lyophilized protein in deionized sterile water to achieve a concentration of 0.1-1.0 mg/mL.

• Storage Preparation: For long-term storage, add glycerol to a final concentration of 5-50% (50% is standard) and aliquot to avoid repeated freeze-thaw cycles.

• Working Conditions: Maintain working aliquots at 4°C for no more than one week.

• Experimental Buffer Selection: Choose buffers that maintain protein stability and function; the protein is typically supplied in a Tris/PBS-based buffer with 6% Trehalose at pH 8.0.

• Purity Verification: The protein purity should be greater than 90% as determined by SDS-PAGE before experimental use .

How can researchers effectively introduce MT-ATP6 mutations into model systems for functional studies?

Researchers can introduce MT-ATP6 mutations into model systems using several established approaches:

• Biolistic Transformation: For yeast models, the mitochondrial genome can be modified using particle bombardment (biolistic transformation) with a gene delivery system like the Particle Delivery Systems PDS-1000/He. This approach has been successfully used to introduce wild-type and mutated ATP6 genes into mitochondria.

• PCR-Based Mutagenesis: The desired MT-ATP6 gene variants can be generated using PCR amplification with appropriate primers containing the mutation of interest. Technologies like GeneArt Invitrogen Gene Synthesis have been used for this purpose.

• Plasmid Construction and Delivery: The wild-type or mutated ATP6 genes can be cloned into appropriate vectors (such as pPT24 plasmid at the EcoRI site) prior to introduction into mitochondria.

• Mitochondrial Recombination: In yeast models, researchers can exploit mitochondrial DNA recombination by crossing ρ− atp6 mut strains with strains like MR10 (where ATP6 is replaced by ARG8m). This allows the variant MT-ATP6 gene to be integrated into a complete mitochondrial genome through recombination.

• Homoplasmy Achievement: After integration, the modified mitochondrial genome segregates to homoplasmy in approximately twelve mitotic divisions (typically without selection pressure in rich 10% glucose media) .

What analytical techniques are most effective for assessing ATP synthase function in the context of MT-ATP6 research?

Several analytical techniques have proven effective for assessing ATP synthase function in MT-ATP6 research:

What controls and validation procedures should be included in experiments using recombinant MT-ATP6 proteins?

Robust experimental design with appropriate controls and validation procedures is essential for MT-ATP6 research:

• Protein Purity Verification: SDS-PAGE analysis should confirm protein purity (>90%) before experimental use.

• Wild-Type Comparison: All mutant variants should be compared with wild-type protein under identical experimental conditions.

• Conservation Alignment Validation: Amino acid conservation analysis across species should validate the evolutionary importance of residues being studied.

• Functional Complementation: In yeast models, functional complementation tests (where mutant variants are assessed for their ability to rescue phenotypes of ATP6-deficient strains) provide strong validation.

• Multiple Methodological Approaches: Using several different methods to assess the same functional outcome increases confidence in results.

• Clinical Correlation: Where possible, correlating experimental findings with clinical data from patients harboring the same mutations strengthens validity.

• Heteroplasmy Controls: For studies involving heteroplasmic mutations, controls with varying mutation loads should be included to establish threshold effects .

How can data from yeast models of MT-ATP6 mutations be effectively translated to understand human mitochondrial disease mechanisms?

Translating findings from yeast models to human mitochondrial disease requires careful consideration of several factors:

• Evolutionary Conservation Assessment: Detailed alignment of yeast and human ATP6 protein sequences establishes the conservation level of specific residues affected by mutations. The strong conservation of residues across species (as shown for mutations like p.I106T corresponding to yeast aI123T) supports the translational relevance of findings.

• Functional Severity Correlation: The severity of biochemical defects in yeast models has shown correlation with clinical disease severity in humans—mutations causing severe dysfunction in yeast (like m.8950G>A, m.9025G>A, and m.9029A>G) are more likely to be pathogenic in humans.

• Multiple Mutation Analysis: Comparing multiple patient-derived mutations in parallel within the same model system allows for relative pathogenicity assessment and classification.

• Heteroplasmy Simulation: While yeast cannot maintain stable heteroplasmy, experiments can be designed to approximate heteroplasmic conditions by mixing different strains or creating systems with controlled expression.

• Clinical Phenotype Correlation: The specific pattern of ATP synthesis defects can be mapped to particular clinical presentations, helping predict which tissues might be affected in human patients.

• Therapeutic Testing Platform: Yeast models provide a platform for testing potential therapeutic approaches before moving to more complex models or clinical applications .

What are the current applications of recombinant MT-ATP6 protein in mitochondrial research beyond mutation studies?

Recombinant MT-ATP6 protein has several research applications beyond mutation studies:

• Structural Analysis: High-purity recombinant protein facilitates structural studies of ATP synthase components using techniques such as X-ray crystallography and cryo-electron microscopy.

• Protein-Protein Interaction Studies: Recombinant MT-ATP6 can be used to identify and characterize interactions with other subunits of the ATP synthase complex and potential regulatory molecules.

• Antibody Development and Validation: The recombinant protein serves as an antigen for developing specific antibodies and as a standard for validating commercially available antibodies.

• Biochemical Mechanism Studies: Purified protein allows detailed investigation of the proton translocation mechanism and bioenergetic properties of ATP synthase.

• Drug Screening: Recombinant protein can be incorporated into screening platforms to identify small molecules that might stabilize mutant proteins or enhance residual ATP synthase function .

How does the understanding of MT-ATP6 function contribute to the development of therapeutic approaches for mitochondrial disorders?

Understanding MT-ATP6 function has important implications for developing therapies for mitochondrial disorders:

• Targeted Drug Development: Detailed knowledge of how specific mutations affect ATP synthase function enables the design of drugs that could specifically address these defects.

• Bypass Strategies: Understanding the bioenergetic consequences of MT-ATP6 mutations helps in developing metabolic bypass strategies to provide alternative energy sources to affected tissues.

• Gene Therapy Approaches: Insights into MT-ATP6 function inform mitochondrial gene therapy approaches, including the development of allotopic expression strategies (expressing mitochondrial genes from the nucleus).

• Heteroplasmy Shifting: Knowledge of mutation thresholds guides approaches to shift heteroplasmy levels below pathogenic thresholds using techniques like mitochondrially-targeted nucleases.

• Pharmacological Chaperones: Understanding protein misfolding or assembly defects caused by mutations enables the development of pharmacological chaperones to stabilize the ATP synthase complex .

What technical challenges remain in the study of recombinant MT-ATP6 and potential solutions?

Several technical challenges persist in MT-ATP6 research, with emerging solutions:

• Membrane Protein Expression: As a highly hydrophobic membrane protein, MT-ATP6 is challenging to express and purify in functional form. Solutions include optimized detergent systems and cell-free expression systems.

• Functional Reconstitution: Reconstituting purified MT-ATP6 into proteoliposomes for functional studies remains technically demanding. Advances in nanodiscs and other membrane mimetics are improving this process.

• Heteroplasmy Modeling: Creating accurate experimental models of heteroplasmy remains difficult. Development of systems with controlled mixed populations or inducible expression systems offers potential solutions.

• Tissue-Specific Effects: Understanding why certain tissues are more affected by MT-ATP6 mutations requires development of tissue-specific models. Advances in patient-derived induced pluripotent stem cells (iPSCs) differentiated into relevant cell types address this challenge.

• In Vivo Monitoring: Non-invasive methods to monitor ATP production in vivo remain limited. Development of novel imaging techniques and metabolic biomarkers is advancing this area .

How do different MT-ATP6 experimental models compare in predicting human disease outcomes?

Different experimental models offer complementary insights for predicting human disease outcomes:

Research suggests that yeast models provide excellent predictions of biochemical defects and reasonable predictions of clinical severity, while mammalian models better capture tissue-specific effects. Combining multiple models yields the most comprehensive understanding of disease mechanisms and potential outcomes .

What are the emerging research directions in MT-ATP6 studies and their potential impact on mitochondrial medicine?

Emerging research directions in MT-ATP6 studies show promise for advancing mitochondrial medicine:

• High-Resolution Structural Studies: Recent advances in cryo-EM technology are enabling detailed structural analysis of ATP synthase, including the MT-ATP6 subunit, providing insights for structure-based drug design.

• Mitochondrial Genome Editing: Development of mitochondrially-targeted CRISPR systems and base editors offers potential for direct correction of MT-ATP6 mutations.

• Compensatory Nuclear Modifications: Research into nuclear genes that modify mitochondrial disease expression could identify targets for therapeutic intervention to compensate for MT-ATP6 defects.

• Tissue-Specific Energy Requirements: Deeper understanding of tissue-specific bioenergetic requirements and thresholds will improve prediction of disease manifestation and progression.

• Metabolic Bypass Therapeutics: Development of small molecules that can bypass the need for ATP synthase by providing alternative energy sources to affected tissues.

• Integrative Multi-Omics Approaches: Combining genomics, proteomics, metabolomics, and clinical data to develop comprehensive models of how MT-ATP6 mutations affect cellular function across different contexts .