Recombinant Helicobacter pylori ATP synthase subunit c (atpE)

What is the structure and basic function of H. pylori ATP synthase subunit c (atpE)?

H. pylori ATP synthase subunit c (atpE) is a small membrane-embedded protein consisting of 105 amino acids with a molecular weight of approximately 11 kDa. The full amino acid sequence is: MKFLALFFLALAGVAFAHDGGMGGMDMIKSYSILGAMIGLGIAAFGGAIGMGNAAAATITGTARNPGVGGKLLTTMFVAMAMIEAQVIYTLVFAIIAIYSNPFLS .

The protein functions as part of the F0 sector of ATP synthase, forming the c-ring structure embedded in the membrane. This c-ring rotates during proton translocation across the membrane, driving the conformational changes in the F1 sector that lead to ATP synthesis. The c subunit forms the ion channel through which protons pass, creating the proton-motive force necessary for ATP synthesis, making it essential for H. pylori energy metabolism.

How is recombinant H. pylori atpE typically expressed and purified for research applications?

Recombinant H. pylori ATP synthase subunit c is typically expressed using prokaryotic expression systems, most commonly E. coli. For optimal expression, the following protocols are generally employed:

• Expression system: The full-length atpE gene (encoding amino acids 1-105) is cloned into a suitable expression vector (e.g., pET series) with an N-terminal His-tag for purification purposes .

• Host strain: E. coli BL21(DE3) or similar strains are used as expression hosts due to their high efficiency for recombinant protein production .

• Purification method: Ni-Nitrilotriacetic acid (Ni-NTA) affinity chromatography is most commonly used to purify the His-tagged protein .

• Purity assessment: SDS-PAGE analysis is used to confirm purity, with successful preparations typically showing >90% purity .

The purified protein is generally stored in Tris/PBS-based buffer containing 6% trehalose at pH 8.0. After reconstitution, the addition of 5-50% glycerol (with 50% being the standard final concentration) is recommended for long-term storage at -20°C/-80°C to maintain stability and prevent freeze-thaw damage .

What is the role of ATP synthase subunit c in H. pylori's energy metabolism?

H. pylori is a microaerophilic bacterium that relies on a specialized energy metabolism system to survive in the harsh environment of the human stomach. The ATP synthase subunit c plays a critical role in this process as part of the F0F1-ATP synthase complex, which is responsible for generating ATP through oxidative phosphorylation.

In the electron transport chain of H. pylori, electrons flow from various substrates (including D-amino acids such as D-proline and D-alanine) through a series of protein complexes including cytochrome bc1, cytochrome c-553, and ultimately to the terminal oxidase cytochrome cbb3 complex . This electron flow generates a proton gradient across the membrane, which is utilized by ATP synthase to synthesize ATP. The c subunit forms the proton channel within the F0 sector, allowing protons to flow back into the cell, driving the rotational motion that powers ATP synthesis.

Research has confirmed the coupling of electron transport to ATP synthesis in H. pylori by using uncoupler reagents that dissipate the proton gradient . This energy production system is critical for H. pylori's survival and pathogenicity, making the ATP synthase complex, including the c subunit, a potential target for therapeutic intervention.

How does H. pylori atpE interact with other subunits of the ATP synthase complex?

The functional H. pylori ATP synthase complex involves multiple subunits that interact in a highly coordinated manner. The c subunit (atpE) forms a ring structure comprising multiple copies arranged in the membrane, which interfaces with other components of the F0 sector (subunits a and b) and the central stalk connecting to the F1 sector.

The exact stoichiometry of the c-ring in H. pylori is not explicitly reported in the provided references, but bacterial c-rings typically contain 8-15 c subunits. These subunits interact through their hydrophobic transmembrane domains to form a stable ring structure. The conserved amino acid sequence in the transmembrane regions, particularly the GIAAFGGAIGMGNAAAATIT portion, is likely involved in c-c subunit interactions and proper ring formation .

The c-ring interacts with subunit a, which contains the half-channels for proton entry and exit. The interaction between subunits a and c is critical for proton translocation and subsequent rotation of the c-ring. The rotation of the c-ring is mechanically coupled to the γ subunit of the F1 sector, driving conformational changes that lead to ATP synthesis.

Understanding these structural interactions is crucial for developing targeted approaches that could potentially disrupt ATP synthase function as a therapeutic strategy against H. pylori infections.

What methodologies are most effective for studying the functional properties of recombinant H. pylori atpE?

Several methodologies have proven effective for studying the functional properties of recombinant H. pylori atpE:

• Reconstitution in liposomes: For functional studies, the purified recombinant atpE protein can be reconstituted into liposomes to mimic its native membrane environment. This approach allows for the investigation of proton translocation activity and interaction with other ATP synthase subunits.

• Electron transport chain reconstitution: As demonstrated with other H. pylori proteins, electron transport chain components can be reconstituted in vitro to demonstrate electron flow. A similar approach could be applied to study ATP synthase function by incorporating the purified atpE into a reconstituted system .

• Spectroscopic analysis: Absorption spectroscopy has been used to characterize other H. pylori respiratory chain components (e.g., cytochrome bc1 complex showing an α peak at 561 nm with a shoulder at 552 nm) . Similar techniques could be applied to study conformational changes in ATP synthase components.

• ATPase activity assays: While not directly applicable to the c subunit alone, ATPase activity assays using NADH colorimetry (as used for SecAN68) can be adapted to study the complete ATP synthase complex containing atpE . This would involve monitoring the changes in NADH absorption at 340 nm to reflect ATP hydrolysis rates.

• Kinetic parameter determination: Enzyme kinetic parameters (Km and Vmax) can be determined using varying substrate concentrations to characterize the functional properties of the ATP synthase complex containing atpE .

How does oxidative stress affect H. pylori ATP synthase expression and function?

H. pylori has developed sophisticated mechanisms to combat oxidative stress, which is particularly relevant given its exposure to reactive oxygen species (ROS) in the gastric environment. Research indicates that oxidative stress significantly impacts H. pylori's energy metabolism, including ATP synthase expression and function.

The HP1021 redox switch protein has been identified as a major regulator of H. pylori's response to oxidative stress . Transcriptomic and proteomic analyses have revealed that HP1021 controls the transcription of 497 genes, with 407 of these related to oxidative stress response . While the search results don't explicitly mention atpE among these regulated genes, the significant impact of HP1021 on energy metabolism implies potential regulation of ATP synthase components.

HP1021 directly regulates glucose consumption by controlling the gluP transporter and has an important impact on maintaining the energetic balance in the cell . Given the central role of ATP synthase in energy production, it is likely that oxidative stress conditions lead to adaptive changes in ATP synthase expression or activity to maintain cellular energy homeostasis under stress.

Research on other bacterial species has shown that oxidative stress can damage ATP synthase components, leading to reduced ATP production. In H. pylori, which has evolved to survive in a harsh oxidative environment, protective mechanisms may exist to preserve ATP synthase function under oxidative conditions, making this an important area for further investigation.

What experimental approaches are most suitable for investigating H. pylori atpE as a potential therapeutic target?

Investigating H. pylori atpE as a potential therapeutic target requires a multifaceted experimental approach:

• Structure-based drug design: Determining the high-resolution structure of H. pylori atpE through X-ray crystallography or cryo-electron microscopy would provide valuable insights for structure-based drug design. The amino acid sequence provided in the search results could be used as a starting point for structural analysis and identification of potential drug binding sites.

• Inhibitor screening assays: Similar to the approach used for SecA inhibitors , screening assays could be developed to identify compounds that specifically inhibit ATP synthase activity. These could be adapted from the NADH colorimetry assay described for SecAN68, modified to detect inhibition of ATP synthesis rather than ATP hydrolysis.

• Site-directed mutagenesis: Creating specific mutations in the atpE gene to identify residues critical for function would help pinpoint potential drug targets. Mutations could be introduced into the recombinant expression construct and the effects on protein function assessed.

• In vitro reconstitution systems: Reconstituted systems containing purified ATP synthase components, including atpE, could be used to directly test the effects of potential inhibitors on ATP synthesis activity. The electron transport chain reconstitution approach described in the search results provides a model for such studies.

• Bacterial growth inhibition assays: Compounds identified as potential ATP synthase inhibitors could be tested for their ability to inhibit H. pylori growth using micro-broth methods similar to those employed for SecA inhibitors .

What are the optimal conditions for expression and purification of recombinant H. pylori atpE protein?

Optimizing the expression and purification of recombinant H. pylori atpE requires careful attention to multiple parameters. Based on the information in the search results and best practices for membrane protein expression, the following conditions are recommended:

Expression Optimization:

• Vector selection: pET-series vectors with T7 promoter systems are recommended for high-level expression, with an N-terminal His-tag for purification purposes .

• E. coli strain: BL21(DE3) or derivatives like C43(DE3) and C41(DE3), which are specifically designed for membrane protein expression .

• Induction conditions: For membrane proteins like atpE, lower induction temperatures (16-25°C) often yield better results than standard 37°C induction. IPTG concentration should be optimized, with typical ranges between 0.1-1.0 mM.

• Growth media: Enriched media such as 2xYT or TB (Terrific Broth) often provide better yields for membrane proteins compared to standard LB medium.

Purification Protocol:

• Cell lysis: Given the membrane-associated nature of atpE, detergent-based lysis (e.g., using n-dodecyl-β-D-maltoside or Triton X-100) is typically more effective than mechanical methods alone.

• Affinity purification: Ni-NTA affinity chromatography is the method of choice for His-tagged proteins . A step gradient of imidazole (20 mM for washing, 250-500 mM for elution) is typically used.

• Buffer composition: Tris/PBS-based buffer with 6% trehalose at pH 8.0 has been shown to be effective for stabilizing the protein .

• Storage conditions: After purification, addition of 5-50% glycerol (with a standard concentration of 50%) and storage at -20°C/-80°C is recommended to maintain stability and prevent freeze-thaw damage .

• Reconstitution: For functional studies, the purified protein should be reconstituted in deionized sterile water to a concentration of 0.1-1.0 mg/mL .

These optimized conditions should yield recombinant H. pylori atpE with purity greater than 90% as determined by SDS-PAGE, suitable for subsequent structural and functional studies.

How can researchers effectively reconstitute and measure the activity of H. pylori ATP synthase containing the atpE subunit?

Reconstituting and measuring the activity of H. pylori ATP synthase containing the atpE subunit requires a carefully designed experimental approach. Drawing from methodologies used for other H. pylori proteins, the following protocol is recommended:

Reconstitution Procedure:

• Component preparation: Purify all necessary subunits of the ATP synthase complex, including the recombinant atpE (c subunit) with appropriate tags for purification and detection .

• Liposome preparation: Prepare liposomes using E. coli lipids or synthetic phospholipids (typically a mixture of phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol at a ratio of 7:2:1) by sonication or extrusion methods.

• Protein incorporation: Incorporate the purified ATP synthase components into liposomes using detergent-mediated reconstitution, followed by detergent removal via dialysis or biobeads.

Activity Measurement Methods:

• ATP synthesis assay: Measure ATP synthesis by energizing the proteoliposomes with an artificial proton gradient (typically generated using acidic buffer outside and basic buffer inside, plus a K+/valinomycin diffusion potential). ATP production can be monitored using a luciferase-based luminescence assay.

• ATP hydrolysis assay: Measure ATP hydrolysis activity using a coupled enzyme assay similar to that described for SecAN68 , where ADP production is coupled to NADH oxidation via pyruvate kinase and lactate dehydrogenase. This allows spectrophotometric monitoring at 340 nm.

• Proton translocation assay: Monitor proton movement across the membrane using pH-sensitive fluorescent dyes like ACMA (9-amino-6-chloro-2-methoxyacridine) or pyranine.

• Electron transport chain coupling: To assess the integration of ATP synthase activity with the electron transport chain, reconstitute the full system as described for cytochrome complexes , including D-amino acid dehydrogenase, cytochrome bc1 complex, cytochrome c-553, and cytochrome cbb3. Upon addition of D-amino acids, measure both oxygen consumption (polarographically) and ATP production (luminometrically).

These methods allow for comprehensive functional characterization of the reconstituted ATP synthase complex containing the atpE subunit.

What techniques can be used to study the interaction between H. pylori atpE and potential inhibitory compounds?

Several sophisticated techniques can be employed to study the interaction between H. pylori atpE and potential inhibitory compounds:

• Enzyme inhibition assays: Using the ATP synthesis or hydrolysis assays described earlier, researchers can determine IC50 values for potential inhibitors. The approach used for SecAN68, employing NADH colorimetry to measure ATPase activity in the presence of varying inhibitor concentrations, provides a good model . In this system, the reaction rate is monitored by measuring NADH consumption at 340 nm, which reflects the ATP hydrolysis rate.

• Surface Plasmon Resonance (SPR): This label-free technique allows real-time monitoring of protein-inhibitor interactions. The purified His-tagged atpE can be immobilized on a sensor chip, and potential inhibitors flowed over the surface to measure binding kinetics (kon and koff) and affinity (KD).

• Isothermal Titration Calorimetry (ITC): ITC provides direct measurement of thermodynamic parameters (ΔH, ΔS, ΔG) of binding between atpE and inhibitors, offering insights into the energetics of the interaction.

• Nuclear Magnetic Resonance (NMR) spectroscopy: For detailed structural analysis of protein-inhibitor complexes, NMR can be used to map the binding interface at the atomic level, identifying specific residues involved in the interaction.

• X-ray crystallography: Co-crystallization of atpE with inhibitors would provide high-resolution structures of the complex, revealing the precise binding mode and allowing structure-based optimization of inhibitors.

• Molecular docking and dynamics simulations: In silico approaches can complement experimental methods, providing models of protein-inhibitor interactions and predicting binding affinities. The full amino acid sequence available for H. pylori atpE can be used to generate structural models for these studies.

• Functional assays in reconstituted systems: Testing inhibitors in the reconstituted electron transport chain system would provide insights into their effects on coupled ATP synthesis in a more physiologically relevant context.

A systematic approach combining these techniques would provide comprehensive characterization of inhibitor binding and functional effects, guiding the optimization of potential therapeutic compounds targeting H. pylori atpE.