Recombinant Hydrogenobaculum sp. ATP synthase subunit c (atpE)

What is the structure and function of ATP synthase subunit c (atpE) in Hydrogenobaculum sp.?

ATP synthase subunit c (atpE) in Hydrogenobaculum sp. is a small, hydrophobic membrane protein consisting of 115 amino acids. The protein forms part of the membrane-embedded Fo sector of ATP synthase, specifically within the c-ring that facilitates proton translocation across the membrane. The amino acid sequence (MKLKTLMLLTLASSIAMADTASSSSSDAHARALFYGLMAVAAGVSIGLGALGAGVGAGSAIRGAEEGMARNPNMAGKLQTIMFIGLAFIETFALYAMLFSIIFVFTGIFSGKAGF) reveals its highly hydrophobic nature, consistent with its membrane-spanning function .

The c-subunit serves as part of the rotary motor in F-type ATP synthases, which convert the proton gradient energy into mechanical rotation, ultimately driving ATP synthesis. In bacterial F-type ATP synthases, the c-ring typically contains 8-15 c subunits arranged in a circle, though the exact number varies by species .

How does the Hydrogenobaculum sp. atpE compare structurally to ATP synthase subunits from other bacterial species?

• Length variation: At 115 amino acids, the Hydrogenobaculum sp. atpE is within the typical range for bacterial c subunits, though lengths vary across species .

• Amino acid composition: The protein contains a high proportion of hydrophobic residues consistent with its membrane-spanning function, including multiple glycine and alanine residues that facilitate tight packing within the c-ring .

• Species-specific adaptations: Unlike some bacterial species that have specific regulatory domains, the Hydrogenobaculum sp. atpE appears to have a more streamlined structure focused on its core proton-conducting function .

The regulatory mechanisms of ATP synthase can vary considerably between species, allowing for fine-tuning of ATP synthase activity according to the physiological needs of each individual organism .

What expression systems are recommended for producing recombinant Hydrogenobaculum sp. atpE?

Based on successful production protocols, E. coli expression systems are recommended for recombinant Hydrogenobaculum sp. atpE protein production . When designing expression experiments:

• Vector selection: Vectors with strong, inducible promoters and appropriate fusion tags (such as His-tag) facilitate both expression and subsequent purification .

• Host strain considerations: E. coli strains optimized for membrane protein expression (such as C41/C43 or BL21 derivatives) often yield better results for hydrophobic proteins like atpE.

• Growth conditions: Expression at lower temperatures (16-25°C) following induction may improve proper folding and incorporation into membranes.

• Extraction protocol: Due to the highly hydrophobic nature of atpE, detergent-based extraction methods using mild detergents like DDM (n-dodecyl β-D-maltoside) are recommended for maintaining protein structure .

The recombinant protein can be produced with an N-terminal His-tag to facilitate purification, with successful expression yielding protein of greater than 90% purity as determined by SDS-PAGE .

What are the recommended storage and handling conditions for recombinant Hydrogenobaculum sp. atpE?

For optimal stability and activity of recombinant Hydrogenobaculum sp. atpE protein:

• Storage temperature: Store the lyophilized protein at -20°C to -80°C for long-term stability .

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

• Stabilization: Addition of glycerol to a final concentration of 5-50% is recommended before aliquoting for long-term storage .

• Aliquoting: Prepare working aliquots to avoid repeated freeze-thaw cycles, which can significantly decrease protein stability and activity .

• Working conditions: When actively using the protein, store working aliquots at 4°C for up to one week to maintain integrity .

• Buffer conditions: The protein is typically stored in Tris/PBS-based buffer with 6% trehalose at pH 8.0, which helps maintain stability during freeze-thaw cycles .

How can researchers investigate the c-ring stoichiometry of Hydrogenobaculum sp. ATP synthase and its impact on bioenergetics?

Investigating c-ring stoichiometry requires sophisticated methodological approaches:

• Cryo-electron microscopy: This technique can resolve the c-ring structure and directly count the number of c subunits. Sample preparation should include purification of intact ATP synthase complexes followed by vitrification on grids.

• Cross-linking mass spectrometry: Chemical crosslinking followed by mass spectrometric analysis can provide insights into the spatial arrangement of c subunits within the ring .

• High-resolution atomic force microscopy: This can be used to visualize and count individual c subunits within isolated c-rings.

• Functional assays correlating proton/ATP ratios: By measuring the H+/ATP stoichiometry in reconstituted systems, researchers can indirectly determine the c-ring composition, as each c subunit typically binds one proton during rotation.

The c-ring stoichiometry directly impacts the bioenergetic efficiency of ATP synthesis, with larger c-rings requiring more protons to synthesize one ATP molecule. In bacterial F-type ATP synthases, the composition typically ranges from 8-15 c subunits arranged in a circle . Determining this number for Hydrogenobaculum sp. would provide valuable insights into its energetic adaptation to extreme environments.

What experimental approaches can be used to study the interaction between atpE and other ATP synthase subunits in Hydrogenobaculum sp.?

Several approaches can elucidate the interactions between atpE and other ATP synthase subunits:

• In vivo protein photo-cross-linking analysis:

  • Introduce unnatural amino acids at specific positions in atpE via site-directed mutagenesis

  • Induce cross-linking under physiological conditions

  • Analyze cross-linked products using high-throughput polyacrylamide gel electrophoresis

  • This method can reveal context-dependent protein-protein interactions under various environmental conditions

• Co-immunoprecipitation studies:

  • Generate antibodies specific to Hydrogenobaculum sp. atpE

  • Perform pull-down experiments followed by mass spectrometry to identify interacting partners

  • Compare interaction patterns under different energetic states

• FRET (Förster Resonance Energy Transfer) analysis:

  • Create fluorescently labeled subunits of the ATP synthase complex

  • Monitor energy transfer between labeled components to map proximity relationships

  • Observe conformational changes during the catalytic cycle

• Yeast two-hybrid (Y2H) analysis:

  • Similar to approaches used with BFA1 and other assembly factors

  • Screen for interactions between atpE and other ATP synthase subunits

  • Verify interactions with in vitro pull-down assays

These techniques can reveal how atpE interacts with other components of the ATP synthase complex, particularly with the central stalk subunits (γ and ε) that connect the Fo and F1 sectors .

How does the atpE subunit contribute to ATP synthase regulation in extremophiles like Hydrogenobaculum sp.?

The regulatory role of atpE (subunit c) in extremophiles involves several mechanisms:

• Proton binding and release:

  • The c subunit contains a conserved carboxyl group (typically from an aspartate or glutamate residue) that binds and releases protons during rotation

  • In extremophiles, modifications to this site can affect proton affinity, altering the threshold for ATP synthesis under extreme pH or temperature conditions

• C-ring structure and adaptation:

  • The c-ring composition may be optimized for function under extreme conditions

  • In thermophiles and acidophiles like Hydrogenobaculum sp., increased hydrophobicity and specific ion-pair interactions can enhance stability

• Interaction with regulatory subunits:

  • The c-ring interacts with the ε subunit, which functions as an inhibitor of ATPase activity through its C-terminal domain

  • The ε subunit can adopt either a compact "hairpin state" or an extended conformation that blocks ATP hydrolysis

  • These regulatory mechanisms prevent wasteful ATP consumption under unfavorable energetic conditions

• Environmental adaptation:

  • Hydrogenobaculum sp., as an extremophile, likely has adaptations in its ATP synthase that allow it to function in its native acidic, high-temperature habitat

  • The c subunit's composition may reflect adaptations for proton binding under extreme pH conditions

Understanding these regulatory mechanisms is particularly important for extremophiles, which must maintain ATP synthesis efficiency under challenging environmental conditions .

What methodologies are most effective for reconstituting functional Hydrogenobaculum sp. atpE into liposomes for biophysical studies?

Reconstitution of functional Hydrogenobaculum sp. atpE into liposomes requires careful optimization:

• Preparation of proteoliposomes:

  • Dissolve purified lipids (typically a mixture of phosphatidylcholine and phosphatidic acid at a 9:1 ratio) in chloroform

  • Evaporate solvent under nitrogen and rehydrate to form multilamellar vesicles

  • Sonicate or extrude to create unilamellar vesicles

  • Solubilize recombinant atpE in mild detergent (e.g., n-dodecyl β-D-maltoside)

  • Mix protein and liposomes at the desired protein-to-lipid ratio (typically 1:50 to 1:200 w/w)

  • Remove detergent by dialysis or adsorption to Bio-Beads

• Verification of successful reconstitution:

  • Freeze-fracture electron microscopy to visualize incorporated proteins

  • Sucrose density gradient centrifugation to separate proteoliposomes from empty liposomes

  • Fluorescence correlation spectroscopy to quantify protein incorporation efficiency

• Functional assays:

  • Proton pumping assays using pH-sensitive fluorescent dyes (e.g., ACMA or pyranine)

  • Patch-clamp electrophysiology to measure proton conductance

  • ATP synthesis assays when co-reconstituted with other ATP synthase subunits

• Thermostability considerations for Hydrogenobaculum sp. proteins:

  • Use lipids with higher transition temperatures for reconstitution experiments

  • Perform functional assays at temperatures reflecting the thermophilic nature of Hydrogenobaculum sp.

  • Include appropriate buffer components (e.g., trehalose) to enhance stability

This methodological approach enables detailed biophysical characterization of Hydrogenobaculum sp. atpE function, particularly its role in proton translocation under various conditions.

How can researchers utilize structural information about atpE to engineer ATP synthases with modified properties?

Structural engineering of ATP synthases based on atpE information involves several strategic approaches:

• Site-directed mutagenesis targeting functional residues:

  • Modify the conserved proton-binding site (typically an aspartate or glutamate residue)

  • Alter hydrophobic residues that contribute to c-ring packing and stability

  • Introduce cysteine residues for cross-linking studies or fluorescent labeling

• C-ring stoichiometry engineering:

  • Modify the curvature-determining residues to alter the number of c subunits in the ring

  • This affects the H+/ATP ratio and therefore the thermodynamic efficiency of ATP synthesis

  • Changes to specific glycine or alanine residues can affect the packing angle between adjacent c subunits

• Chimeric constructs:

  • Create fusion proteins combining regions from different species to investigate domain-specific functions

  • For example, combine the Hydrogenobaculum sp. atpE with regions from mesophilic bacteria to identify thermostability determinants

  • Test chimeric ATP synthase complexes, similar to studies with thermophilic Bacillus PS3 and spinach

• Regulatory mechanism engineering:

  • Modify the interaction interface between the c-ring and regulatory subunits like ε

  • Engineer switches responsive to different cellular signals

  • The ATP-dependent conformational change of the ε-subunit provides a template for designing regulated ATP synthases

These approaches could lead to engineered ATP synthases with properties such as altered temperature optima, modified regulatory responses, or different H+/ATP ratios suitable for biotechnological applications. The compact nature of the Hydrogenobaculum sp. atpE (115 amino acids) makes it particularly amenable to protein engineering approaches .

What are common challenges in expressing and purifying recombinant Hydrogenobaculum sp. atpE and how can they be addressed?

Researchers frequently encounter several challenges when working with atpE:

• Low expression yields:

  • Challenge: Hydrophobic membrane proteins often express poorly in standard systems

  • Solution: Use specialized E. coli strains (C41/C43, Lemo21), lower induction temperature (16-20°C), and extend expression time (overnight induction)

  • Alternative approach: Consider cell-free expression systems optimized for membrane proteins

• Protein aggregation:

  • Challenge: atpE tends to aggregate during extraction and purification

  • Solution: Optimize detergent selection (screen DDM, LDAO, LMNG) and concentration; maintain samples at 4°C during processing

  • Preventive measure: Add stabilizing agents like glycerol (5-15%) and specific lipids to purification buffers

• Low purity after initial purification:

  • Challenge: Contaminants persist after affinity chromatography

  • Solution: Implement multi-step purification including size exclusion chromatography following initial His-tag purification

  • Quality control: Verify final purity by SDS-PAGE (>90% purity should be achievable)

• Protein instability during storage:

  • Challenge: Activity loss during freeze-thaw cycles

  • Solution: Store as lyophilized powder or aliquot with 6% trehalose in storage buffer

  • Best practice: Avoid repeated freeze-thaw cycles by preparing appropriate working aliquots

• Functional verification:

  • Challenge: Confirming that purified atpE retains native structure

  • Solution: Circular dichroism spectroscopy to verify secondary structure content

  • Functional test: Reconstitution into liposomes followed by proton transport assays

How can researchers distinguish between the effects of mutations in atpE versus other ATP synthase subunits?

Distinguishing mutation effects across different ATP synthase subunits requires systematic approaches:

• Complementation studies:

  • Generate a deletion strain lacking the native atpE gene

  • Complement with plasmid-expressed wild-type or mutant versions

  • Compare growth phenotypes and ATP synthesis capacity

  • This approach isolates the effect of atpE mutations from other subunits

• Reconstitution of hybrid complexes:

  • Purify individual ATP synthase components from wild-type sources

  • Introduce only the mutated atpE component into reconstitution experiments

  • Measure ATP synthesis/hydrolysis activities of these hybrid complexes

  • The difference between hybrid and wild-type complexes reveals atpE-specific effects

• Structural analysis techniques:

  • Cryo-EM of ATP synthase complexes containing wild-type or mutant atpE

  • Compare structures to identify conformational changes propagated to other subunits

  • Cross-linking mass spectrometry to detect altered subunit interactions

• Subunit-specific inhibitors:

  • Apply inhibitors targeting specific subunits in combination with atpE mutations

  • Additive effects suggest independent mechanisms

  • Synergistic or antagonistic effects indicate interaction between mutation and inhibitor target

• In vivo cross-linking analysis:

  • Implement high-throughput in vivo protein photo-cross-linking

  • Compare cross-linking patterns between wild-type and mutant proteins

  • Changes in cross-linking patterns reveal altered interactions with other subunits

These approaches systematically isolate the effects of atpE mutations from those in other subunits, enabling precise characterization of structure-function relationships.

How can recombinant Hydrogenobaculum sp. atpE be utilized in studies of extremophile adaptation mechanisms?

Recombinant Hydrogenobaculum sp. atpE provides valuable insights into extremophile adaptations:

These approaches leverage recombinant Hydrogenobaculum sp. atpE to understand fundamental mechanisms of protein adaptation to extreme environments, with potential applications in protein engineering for industrial processes.

What role does ATP synthase subunit c play in the development of antimicrobial strategies, and how can Hydrogenobaculum sp. atpE research contribute to this field?

ATP synthase subunit c represents a promising antimicrobial target with several research directions:

• Comparative inhibitor studies:

  • Screen inhibitor compounds against atpE from pathogenic bacteria versus Hydrogenobaculum sp.

  • Identify structural determinants of inhibitor specificity

  • The divergent structure of extremophile atpE can highlight conserved vulnerability points

• Regulatory mechanism targeting:

  • Study the ε subunit's inhibitory interaction with the c-ring

  • Design small molecule compounds that mimic the lacking C-terminal tip of subunit ε, potentially relieving its inhibitory effect

  • Such compounds could stimulate ATP hydrolysis and deplete bacterial ATP pools, particularly effective against bacteria with low cellular energy reserves

• Essential function disruption:

  • Target the proton-binding site in atpE, which is essential for ATP synthesis

  • The distinct c-ring composition in different bacterial species offers selective targeting potential

  • Hydrogenobaculum sp. atpE structure provides a reference point for identifying conserved versus variable regions

• Fragment-based drug discovery approaches:

  • Use Hydrogenobaculum sp. atpE in structural studies to identify binding pockets

  • Screen fragment libraries for specific binding to bacterial atpE

  • Develop these fragments into antimicrobial leads with atpE-specific activity

• Resistance mechanism studies:

  • Generate mutations in atpE that confer resistance to known inhibitors

  • Compare with clinical resistance mutations

  • Hydrogenobaculum sp. atpE can serve as an outgroup to highlight convergent resistance mechanisms

These approaches leverage Hydrogenobaculum sp. atpE research to advance antimicrobial development, particularly against organisms where ATP synthase inhibition represents a viable strategy.

How can researchers utilize high-throughput approaches to study the interaction landscape of ATP synthase subunit c across different physiological conditions?

Advanced high-throughput methodologies offer powerful approaches to study atpE interactions:

• In vivo protein photo-cross-linking analysis pipeline:

  • Introduce unnatural amino acids at specific positions in atpE via site-directed mutagenesis

  • Induce cross-linking under various physiological conditions

  • Analyze the cross-linked products via high-throughput polyacrylamide gel electrophoresis

  • This approach reveals how ATP synthase conformational states respond to environmental changes

• Hydrogen-deuterium exchange mass spectrometry (HDX-MS):

  • Expose ATP synthase complexes to deuterated buffers under different conditions

  • Monitor exchange rates at peptide resolution

  • Identify regions of atpE with altered solvent accessibility or dynamics

  • This method can detect subtle conformational changes in response to pH, temperature, or energy state

• Multiplexed co-immunoprecipitation studies:

  • Generate affinity-tagged versions of atpE and other ATP synthase subunits

  • Perform parallel pull-downs under different physiological conditions

  • Analyze interaction partners by mass spectrometry

  • Quantify changes in the interaction network across conditions

• High-throughput mutagenesis coupled with functional assays:

  • Create comprehensive libraries of atpE variants using saturation mutagenesis

  • Screen for altered function under different physiological conditions

  • Identify residues critical for specific environmental adaptations

These high-throughput approaches can reveal how the ATP synthase exists as an equilibrium between different functional states in cells, allowing bacterial ATP synthases to proportionally and instantly switch between reversible functional states in response to changing environmental conditions .

What potential biotechnological applications exist for engineered versions of Hydrogenobaculum sp. atpE?

Engineered versions of Hydrogenobaculum sp. atpE offer several promising biotechnological applications:

• Bioenergy applications:

  • Engineer atpE to optimize ATP synthesis efficiency under specific conditions

  • Develop synthetic ATP synthases with altered H+/ATP ratios for biofuel production systems

  • Create ATP synthases capable of functioning with alternative ion gradients (Na+ instead of H+)

• Biosensors for extreme environments:

  • Develop atpE-based sensors for monitoring environmental parameters in extreme conditions

  • Engineer proteins to change conformation or activity in response to specific stimuli

  • Utilize the inherent stability of extremophile proteins for long-term sensing applications

• Protein scaffolds for nanobiotechnology:

  • Use the self-assembling c-ring structure as a template for creating nanoscale devices

  • Engineer binding sites onto the c-ring for precise spatial arrangement of functional molecules

  • The thermostability of Hydrogenobaculum sp. proteins provides advantages for harsh conditions

• Drug delivery systems:

  • Develop modified c-rings as carriers for therapeutic compounds

  • Engineer release mechanisms based on ATP synthase conformational changes

  • Utilize the membrane-integrating properties of atpE for targeted delivery

• Bioelectronic interfaces:

  • Create hybrid devices combining biological ATP synthases with electronic components

  • Develop energy harvesting systems based on proton gradients

  • The extreme stability of Hydrogenobaculum sp. proteins enhances compatibility with non-biological components

These applications leverage the unique properties of Hydrogenobaculum sp. atpE, particularly its stability under extreme conditions and its role in energy transduction processes.