Recombinant Lactobacillus fermentum ATP synthase subunit delta (atpH)

What expression systems are most suitable for producing recombinant L. fermentum atpH?

Two primary expression systems have been documented for recombinant production of L. fermentum atpH:

• E. coli expression system: This is a widely used system for recombinant protein production due to its rapid growth, high protein yields, and well-established protocols. Commercial recombinant L. fermentum atpH is available from E. coli expression systems with purity >85% as determined by SDS-PAGE .

• Yeast expression system: This system offers advantages for proteins requiring eukaryotic post-translational modifications. Commercial recombinant L. fermentum atpH is also available from yeast expression systems with similar purity levels (>85%) .

When planning expression of ATP synthase subunits, researchers may consider approaches similar to those used for other ATP synthase components. For instance, with the ATP synthase c subunit from spinach chloroplast, various vectors including pMAL-c2x, pET-32a(+), and pFLAG-MAC have been used to compare alternate modes of expression . For bacterial expression, transformation of E. coli followed by culture in LB-glucose expression medium (1.0% tryptone, 0.5% yeast extract, 0.4% glucose, 0.5% NaCl, with appropriate antibiotics) is typical, with expression induced using IPTG .

What are the optimal conditions for storing recombinant L. fermentum atpH?

For optimal storage of recombinant L. fermentum atpH, the following conditions are recommended:

• Long-term storage: Store at -20°C, or for extended storage, conserve at -20°C or -80°C .

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

• Reconstitution protocol:

  • Briefly centrifuge the vial prior to opening to bring contents to the bottom

  • Reconstitute protein 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

  • The default final concentration of glycerol is typically 50%

• Shelf life:

  • Liquid form: Generally 6 months at -20°C/-80°C

  • Lyophilized form: Generally 12 months at -20°C/-80°C

It is important to note that repeated freezing and thawing is not recommended as it may lead to protein denaturation and loss of activity .

How can I verify the expression and purity of recombinant L. fermentum atpH?

Verification of expression and purity of recombinant L. fermentum atpH can be accomplished through multiple complementary techniques:

• SDS-PAGE analysis: Prepare a 12% polyacrylamide gel with samples of total cell lysate along with appropriate controls. Commercial preparations typically show purity >85% using this method . For visualization, Coomassie blue staining can reveal the protein band corresponding to the expected molecular weight.

• Immunoblotting: Following SDS-PAGE separation, proteins can be transferred to a suitable membrane and probed with antibodies specific to atpH or to any tags incorporated into the recombinant construct. This approach was used successfully for confirming expression of the c subunit of ATP synthase in previous studies .

• Mass spectrometry: For definitive identification and verification of sequence integrity, peptide mass fingerprinting or tandem mass spectrometry can be employed. This allows for confirmation of the complete sequence: MSRLDQKTVANRYARAIFELAQEDGQLDQTYQELVSVRQVFLDNPSLAPLLAGVDLGIKEKQALVDQVKEGASKYVANLLQMAFDYRRMSSDMVAIVDEFERRYDEKHKRVHAEVVTAVQLDETRRNQLRDNLAARLGAQEIVLNEKVDPTILGGVVVKTANQTLDGSIKTKIEQIRRLIV .

• Functional assays: Activity measurements can confirm that the purified protein retains its biological function, particularly if it is to be used in reconstitution experiments or enzymatic studies.

What methodologies are available for measuring ATP synthase activity in recombinant L. fermentum atpH preparations?

Several methodologies can be employed to measure the activity of ATP synthase containing recombinant L. fermentum atpH:

• Combined ATP synthesis and hydrolysis measurement: A sophisticated approach involves measuring both synthetic and hydrolytic activities concurrently using instruments like the Seahorse XF96 Analyzer. This method measures oxygen consumption (indicative of ATP synthesis) and pH changes (acidification rates, indicative of ATP hydrolysis) in different channels . ATP synthesis is determined by measuring oxygen consumption induced by saturating concentrations of ADP (State 3 respiration), while ATP hydrolysis is measured through changes in pH.

• Proton transport measurement: During ATP hydrolysis, protons are generated and transported across membranes when ATP synthase works in reverse. This can be measured as the acidification rate of the sample. In intact, coupled mitochondria or membrane preparations, approximately one proton is net transported per 2.67 molecules of ATP hydrolyzed .

• Reconstitution experiments: For detailed functional studies, recombinant atpH can be used in reconstitution experiments to rebuild the ATP synthase complex. This approach has been explored with other ATP synthase subunits, such as the c subunit from spinach chloroplast . Successful reconstitution provides a platform for investigating factors that influence the stoichiometric variation and functional characteristics of the intact complex.

• Inhibitor studies: ATP synthase activity can be characterized by its response to known inhibitors. For example, (+)-Epicatechin has been shown to inhibit ATP synthase hydrolytic activity . Differential responses to inhibitors can provide insights into the structural and functional integrity of complexes containing the recombinant subunit.

How does the structure and function of L. fermentum atpH compare with ATP synthase delta subunits from other species?

Comparison of L. fermentum atpH with ATP synthase delta subunits from other species reveals both conserved features and species-specific adaptations:

• Functional conservation: The fundamental role of the delta subunit in the central stalk of ATP synthase is conserved across species. In all cases, it participates in the rotary mechanism that couples ATP turnover in the F1 domain to proton translocation through F0 .

• Structural comparison with mitochondrial ATP synthase: While L. fermentum atpH is part of a bacterial F-type ATP synthase, its functional counterpart in mitochondria also participates in energy conversion through a similar mechanism. The mitochondrial ATP synthase produces ATP from ADP in the presence of a proton gradient across the membrane generated by electron transport complexes of the respiratory chain .

• Sequence and size variations: The L. fermentum atpH protein consists of 181 amino acids , which may differ in length from homologs in other species. These differences can reflect adaptations to specific environmental conditions or energy requirements of the organism.

• Regulatory adaptations: Different species may exhibit variations in how ATP synthase activity is regulated. For example, in the probiotic bacterium Limosilactobacillus reuteri, transcriptional regulation networks influence energy metabolism genes, potentially including ATP synthase components . Understanding these species-specific regulatory mechanisms can provide insights into how different organisms optimize energy production under various conditions.

What challenges might arise in expressing and purifying recombinant L. fermentum atpH, and how can they be addressed?

Several challenges may arise during the expression and purification of recombinant L. fermentum atpH, along with potential solutions:

• Protein solubility issues:

  • Challenge: ATP synthase subunits may form inclusion bodies in heterologous expression systems.

  • Solution: Expression conditions can be optimized by adjusting temperature (lower temperatures often favor soluble expression), IPTG concentration, and induction time. Co-expression with chaperones can also improve solubility, as demonstrated in studies with other ATP synthase subunits where co-transformation with pOFXT7KJE3 was employed .

• Protein stability problems:

  • Challenge: The recombinant protein may be unstable during purification or storage.

  • Solution: Include protease inhibitors (such as 2% v/v Protease Inhibitor Cocktail) in lysis buffers . For storage, add glycerol to a final concentration of 5-50% and store in small aliquots to avoid repeated freeze-thaw cycles .

• Low expression yields:

  • Challenge: Insufficient protein production for experimental needs.

  • Solution: Explore alternative expression vectors. For instance, comparing pMAL-c2x, pET-32a(+), and pFLAG-MAC vectors can identify the optimal system for expression . Additionally, codon optimization for the expression host can significantly improve yields.

• Purification difficulties:

  • Challenge: Achieving high purity levels required for structural or functional studies.

  • Solution: Implement multi-step purification strategies, potentially including affinity chromatography (if tags are incorporated), ion exchange chromatography, and size exclusion chromatography. Commercial preparations achieve >85% purity using appropriate purification protocols .

• Functional verification challenges:

  • Challenge: Confirming that the recombinant protein retains its native functional properties.

  • Solution: Employ activity assays that measure both ATP synthesis and hydrolysis capabilities . For comprehensive assessment, reconstitution experiments can be conducted to rebuild the ATP synthase complex with the recombinant subunit.

How can recombinant L. fermentum atpH be used in reconstitution studies to investigate ATP synthase complex assembly and function?

Reconstitution studies using recombinant L. fermentum atpH can provide valuable insights into ATP synthase complex assembly and function:

• Component-by-component reconstitution approach:

  • Purify individual ATP synthase subunits, including recombinant atpH

  • Systematically combine subunits under controlled conditions to monitor assembly

  • Use techniques such as native PAGE, analytical ultracentrifugation, or cryo-electron microscopy to verify correct assembly

  • This approach has been explored with other ATP synthase subunits, such as the c subunit from spinach chloroplast

• Stoichiometry investigations:

  • Recombinant expression systems enable precise control over subunit stoichiometry during reconstitution

  • This allows investigation of factors that influence the stoichiometric variation of intact complexes

  • Molecular biology techniques that cannot be applied to native complexes become feasible with recombinant subunits

• Functional characterization of reconstituted complexes:

  • Assay ATP synthesis activity by measuring oxygen consumption induced by ADP

  • Assess ATP hydrolysis activity by monitoring proton production and acidification rates

  • Compare activities between reconstituted complexes and native ATP synthase to validate functional reconstitution

• Investigation of forward and reverse activities:

  • Reconstituted complexes can be used to study both ATP synthesis (forward) and ATP hydrolysis (reverse) activities

  • Special assays can quantify the proportion of ATP synthase working in forward versus reverse directions under different conditions

  • This approach can reveal insights into energy conservation mechanisms and regulatory features

Properties of Recombinant L. fermentum ATP Synthase Subunit Delta (atpH)

Comparison of ATP Synthase Function Across Different Systems