Recombinant Campylobacter jejuni ATP synthase subunit c (atpE)

What expression systems are effective for producing recombinant C. jejuni atpE?

Several expression systems have been documented for the production of recombinant C. jejuni atpE, with E. coli being the most commonly utilized. Research indicates that successful expression has been achieved using:

• E. coli expression systems: Most frequently reported and commercially available recombinant atpE is produced in E. coli, likely using T7 or similar strong promoters .

• Alternative expression hosts: While less common, other expression systems that have been utilized include:

  • Yeast-based expression systems

  • Baculovirus-infected insect cells

  • Mammalian cell expression systems

When designing expression constructs, researchers should consider:

• Adding affinity tags (such as His-tag) to facilitate purification

• Optimizing codon usage for the chosen expression host

• Appropriate signal peptides if secretion is desired

The choice of expression system should be guided by the specific research requirements, including the need for post-translational modifications, protein folding considerations, and final application of the recombinant protein .

How should recombinant C. jejuni atpE be stored to maintain stability?

Maintaining the stability of recombinant C. jejuni atpE requires specific storage conditions based on research findings:

Recommended storage protocol:

• Store stock solutions at -20°C for routine storage

• For extended storage periods, maintain at -80°C

• Keep working aliquots at 4°C for up to one week

• Avoid repeated freeze-thaw cycles as they significantly compromise protein integrity

• Store in buffer containing glycerol (typically 50% final concentration) to prevent freeze damage

Commercial preparations often come in a liquid form containing glycerol as a stabilizing agent. Storage buffers frequently include Tris-based or PBS-based formulations, sometimes supplemented with trehalose (6%) at pH 8.0 to enhance stability .

What role does atpE play in C. jejuni pathogenesis and virulence?

While atpE is not directly classified as a classical virulence factor, its role in energy metabolism is indirectly critical to C. jejuni pathogenesis:

• Energy provision for virulence mechanisms: ATP synthase provides the energy required for various virulence processes, including motility, invasion, and toxin production. Research on C. jejuni virulence has demonstrated that energy-dependent processes are essential for successful host infection .

• Adaptation to environmental stresses: During infection, C. jejuni must adapt to changing environments, including acid stress in the stomach. Studies have shown that C. jejuni modulates gene expression in response to acid shock, which may include adjustments in energy metabolism genes .

• Relationship to known virulence factors: Genome-wide studies of C. jejuni have identified various virulence factors, including the cytolethal distending toxin (CDT) and MlaEFD proteins, which require energy for their synthesis and function. The atpE gene product contributes to this energy provision .

• Survival in host environments: The ability of C. jejuni to survive in diverse host environments, including microaerophilic conditions in the gut, may depend on efficient energy metabolism systems including ATP synthase .

Research by Sałamaszyńska-Guz et al. (2022) demonstrated that alterations in C. jejuni protein expression can significantly impact virulence traits including biofilm formation, host cell attachment, and invasion .

How can researchers verify the functionality of recombinant C. jejuni atpE?

To confirm the functionality of recombinant C. jejuni atpE, researchers can employ several complementary approaches:

• Spectroscopic analysis:

  • CO differential spectrum assays can be used to determine oxygen-binding capacity, similar to methods used for C. jejuni hemoglobin studies

  • Circular dichroism (CD) spectroscopy to verify proper protein folding

• Functional reconstitution assays:

  • Reconstitution into liposomes or membrane vesicles

  • Measurement of proton translocation activity using pH-sensitive fluorescent dyes

  • ATP synthesis assays in reconstituted systems

• Binding studies:

  • Evaluation of interaction with other ATP synthase subunits

  • Assessment of binding to specific inhibitors

• Genetic complementation:

  • Introduction of the recombinant atpE gene into atpE-deficient strains

  • Evaluation of restoration of ATP synthesis function in vivo

• Structural integrity verification:

  • Size-exclusion chromatography to confirm oligomeric state

  • SDS-PAGE analysis under non-reducing and reducing conditions

  • Mass spectrometry to verify molecular mass and post-translational modifications

The specific method chosen should align with the research objectives and available laboratory resources. Combining multiple approaches provides the most robust verification of functionality .

What is the evolutionary significance of atpE in Campylobacter species?

The evolutionary aspects of atpE in Campylobacter species reveal important insights about bacterial adaptation and speciation:

• Conservation across Campylobacter species: The atpE gene is conserved across Campylobacter species, reflecting its essential role in energy metabolism. Research on horizontal gene transfer in Campylobacter has shown that core metabolic genes like those encoding ATP synthase components can be subject to evolutionary pressures .

• Horizontal gene transfer patterns: Studies have examined horizontal gene transfer (HGT) between C. jejuni and C. coli. While the uncA gene (encoding the ATP synthase alpha subunit) has been identified as subject to HGT between these species, the specific patterns for atpE are less documented but potentially similar .

• Sequence variation among strains: Different strains of C. jejuni (such as serotype O:23/36 and serotype O:6) possess atpE genes with some sequence variations, which may reflect adaptation to different environmental niches or hosts .

• Relationship to pathogenicity islands: The evolution of metabolic genes in Campylobacter may be linked to pathogenicity islands. Research has identified interactions between core metabolic functions and virulence factor expression, suggesting co-evolution of these systems .

The study by Sheppard et al. described in search result found that approximately 4.7% of C. jejuni sequence types contained imported alleles from C. coli, demonstrating interspecies genetic exchange that could potentially involve metabolic genes like atpE.

How does atpE interact with other components of the ATP synthase complex in C. jejuni?

The interaction of atpE with other ATP synthase components follows a specific structural arrangement crucial for functional energy generation:

• C-ring formation: Multiple copies of the atpE protein (typically 10-15 subunits) assemble to form the c-ring structure in the bacterial membrane, creating a central ion channel. This ring is essential for the rotary mechanism of ATP synthesis.

• Interaction with a-subunit: The c-ring interfaces with the a-subunit (encoded by atpB) to form the complete proton channel. This interaction creates the pathway for proton translocation across the membrane.

• Interaction with the F1 sector: The c-ring connects to the γ and ε subunits of the F1 sector, coupling proton movement through F0 to conformational changes in F1 that drive ATP synthesis.

• Membrane integration: As demonstrated by research on membrane proteins in C. jejuni, atpE is integrated into the lipid bilayer through its hydrophobic transmembrane helices, with specific lipid interactions potentially important for function.

While the search results don't provide specific structural details about C. jejuni ATP synthase components, the general architecture of F-type ATP synthases is well conserved across bacterial species. Research tools that have been used to study protein-protein interactions in other C. jejuni systems, such as bacterial two-hybrid screens used to investigate the CtsP-CtsX interaction , could potentially be applied to study atpE interactions.

What methodologies are most effective for purifying recombinant C. jejuni atpE?

Purification of recombinant C. jejuni atpE presents specific challenges due to its hydrophobic nature as a membrane protein. Based on research practices, the following methodologies are most effective:

• Affinity chromatography:

  • His-tag purification using immobilized metal affinity chromatography (IMAC) is the method of choice for His-tagged versions of the protein

  • Nickel or cobalt resins are commonly used with imidazole elution gradients

  • Typical binding buffers contain 20-50 mM Tris-HCl (pH 8.0), 300-500 mM NaCl, and 5-10 mM imidazole

• Detergent solubilization strategies:

  • Mild detergents (n-dodecyl-β-D-maltoside, digitonin, or CHAPS) for initial membrane solubilization

  • Detergent concentration must be maintained above critical micelle concentration (CMC) throughout purification

• Size exclusion chromatography (SEC):

  • Secondary purification step to remove aggregates and further purify the protein

  • Typically performed in buffers containing 0.03-0.05% of the selected detergent

• Ion exchange chromatography:

  • Can be used as an additional purification step based on the protein's isoelectric point

  • Useful for removing contaminating proteins not separated by affinity methods

• Assessment of purity:

  • SDS-PAGE with Coomassie or silver staining (>90% purity standard)

  • Western blotting with anti-His antibodies for tagged versions

A typical workflow combines affinity chromatography as the capture step, followed by SEC and/or ion exchange chromatography as polishing steps. Throughout the purification process, it's critical to maintain conditions that prevent protein aggregation due to the hydrophobic nature of membrane proteins.

What experimental approaches can identify the role of atpE in C. jejuni stress responses?

Investigating the role of atpE in C. jejuni stress responses requires multi-faceted experimental approaches:

• Genetic manipulation strategies:

  • Generation of atpE deletion mutants using methods similar to those described for other C. jejuni genes (e.g., clpB deletion using chloramphenicol resistance cassette insertion)

  • Complementation studies to confirm phenotype specificity

  • Site-directed mutagenesis of specific residues to identify critical functional domains

• Stress exposure assays:

  • Acid stress experiments (pH 4.5) to mimic stomach transit, as described in Reid et al.

  • Oxygen stress tests to evaluate survival under varying oxygen concentrations

  • Nutrient limitation assays

  • Temperature stress evaluations

• Transcriptomic and proteomic analysis:

  • RNA-seq or microarray analysis to measure atpE expression under stress conditions

  • Quantitative proteomics to determine if AtpE protein levels change during stress responses

  • Comparative proteome analysis between wild-type and atpE mutants, similar to approaches used for tlyA studies

• In vivo models:

  • Animal infection models (such as piglet stomach models) to study atpE expression during in vivo stress conditions

  • Cell culture models to evaluate bacterial responses to host cell interaction

• Energy metabolism measurements:

  • Measurement of ATP levels under different stress conditions

  • Membrane potential assessment using fluorescent probes

  • Oxygen consumption rate determination

Reid et al. demonstrated that C. jejuni modulates gene expression during acid shock and stomach transit, which could involve ATP synthase components as part of the metabolic adaptation to stress.

What is the relationship between ATP synthase function and C. jejuni adaptation to microaerophilic conditions?

C. jejuni's adaptation to microaerophilic conditions is intricately linked to ATP synthase function:

• Energy generation under oxygen limitation:

  • As a microaerophilic organism, C. jejuni has evolved specific mechanisms to generate energy under low oxygen conditions

  • ATP synthase plays a critical role in maintaining energy homeostasis in these environments

  • The atpE subunit contributes to the proton translocation machinery that functions effectively even under reduced oxygen levels

• Integration with alternative respiratory pathways:

  • C. jejuni possesses alternative electron acceptors for respiration under microaerophilic conditions

  • ATP synthase integrates with these pathways to maintain energy production

  • Studies have shown C. jejuni upregulates genes involved in using nitrite as a terminal electron acceptor during stomach transit, which connects to energy generation systems

• Oxygen-dependent regulation:

  • Research on C. jejuni hemoglobin (CHb) demonstrated that oxygen-binding proteins improve growth under varying oxygen conditions

  • ATP synthase expression may be similarly regulated in response to oxygen availability

• Experimental evidence:

  • When C. jejuni single domain hemoglobin (CHb) was expressed in E. coli, it improved oxygen utilization efficiency and overcame oxygen shortage in bioreactors

  • Similar principles may apply to ATP synthase optimization in C. jejuni's natural microaerophilic environment

Xu et al. (2015) demonstrated that "improved oxygen utilization efficiency of cells" helps overcome oxygen limitations in culture conditions , suggesting ATP synthase's role in energy metabolism is crucial for adaptation to microaerophilic environments.

How can recombinant C. jejuni atpE be used in structural studies?

Structural characterization of recombinant C. jejuni atpE requires specialized approaches for membrane proteins:

• X-ray crystallography strategies:

  • Protein-detergent complexes can be prepared for crystallization trials

  • Lipidic cubic phase (LCP) crystallization may be particularly suitable

  • Examples of successful membrane protein structure determination, such as the case of Cj0982 (cysteine transporter) from C. jejuni, can provide methodological guidance

  • Addition of stabilizing antibody fragments or fusion partners may enhance crystallization success

• Cryo-electron microscopy (Cryo-EM) approaches:

  • Single-particle analysis of purified ATP synthase complexes

  • Analysis of reconstituted atpE c-rings

  • Incorporation into nanodiscs or amphipols to maintain native-like environment

• Nuclear Magnetic Resonance (NMR) studies:

  • Solution NMR for specific domains or fragments

  • Solid-state NMR for full-length protein in membrane mimetics

  • Selective isotopic labeling strategies to focus on functional regions

• Computational prediction and modeling:

  • Homology modeling based on other bacterial ATP synthase c subunits

  • Molecular dynamics simulations to study conformational dynamics

  • Integration of experimental constraints with in silico approaches

• Sample preparation considerations:

  • Protein must be maintained in detergent micelles or membrane mimetics

  • Concentration and buffer optimization is critical

  • Temperature stability must be assessed prior to structural studies

The structural study of C. jejuni Cj0982 (CjaA) described by Müller et al. provides a methodological framework that could be adapted for atpE structural studies. Their work used X-ray crystallography to determine the structure of this periplasmic binding protein and revealed important functional insights .

What factors influence the recombinant expression levels of C. jejuni atpE?

Multiple factors significantly impact the expression levels of recombinant C. jejuni atpE:

• Expression system selection:

  • E. coli-based systems are most commonly used but may require optimization

  • Codon optimization for the host organism can significantly improve expression

  • Specialized E. coli strains designed for membrane protein expression (e.g., C41(DE3), C43(DE3)) often yield better results

• Vector design considerations:

  • Promoter strength affects expression level (T7 promoters are commonly used)

  • Inclusion of appropriate secretion signals if applicable

  • Fusion tags can impact both expression and solubility:

    • N-terminal His-tags have been successfully used

    • Fusion partners like MBP or SUMO can improve folding

• Growth and induction parameters:

  • Lower temperatures (16-25°C) during induction often improve membrane protein folding

  • Inducer concentration optimization (IPTG for T7-based systems)

  • Media composition affects biomass and protein yield

  • Growth phase at induction time influences expression success

• Membrane protein-specific challenges:

  • Overexpression can lead to toxicity due to membrane crowding

  • Lipid composition of the host may affect proper insertion

  • Potential formation of inclusion bodies requires optimization of solubilization strategies

• Post-induction handling:

  • Harvest timing optimization

  • Gentle cell lysis methods to preserve membrane integrity

  • Appropriate detergent selection for solubilization

Research conducted on other C. jejuni membrane proteins suggests that careful optimization of these parameters is essential. Studies with recombinant expression of C. jejuni proteins, including various ATP synthase subunits, have demonstrated that specialized approaches for membrane proteins significantly improve yields .

How does the function of atpE relate to C. jejuni biofilm formation and colonization?

The relationship between atpE function and C. jejuni biofilm formation and colonization involves several interconnected processes:

• Energy provision for biofilm-associated processes:

  • ATP synthesis provides energy required for adhesion, motility, and production of extracellular matrix components

  • Biofilm formation in C. jejuni has been shown to be energy-dependent, with multiple studies demonstrating the importance of energy metabolism for this process

• Connection to known biofilm regulators:

  • Studies of C. jejuni virulence factors have identified proteins like Peb4 that are critical for both biofilm formation and cell adhesion

  • As demonstrated by Asakura et al., deletion of the peb4 gene significantly reduced biofilm formation capacity

  • The energy provided by ATP synthase supports the function of these biofilm-regulating proteins

• Metabolic adaptation during colonization:

  • C. jejuni must adapt its metabolism during different stages of host colonization

  • ATP synthase activity may be modulated to support changing energy demands during biofilm formation and host cell attachment

  • Proteomic analyses of C. jejuni mutants with impaired biofilm formation have revealed altered expression of proteins involved in energy metabolism

• Empirical evidence from related studies:

  • Research on C. jejuni tlyA mutants demonstrated reduced biofilm formation, host cell attachment, invasion, and survival

  • These phenotypes were linked to changes in proteome composition, which could include altered energy metabolism

  • The fact that atpE supports these energy-demanding processes suggests its function is relevant to biofilm formation and colonization

The study by Asakura et al. demonstrated that the Peb4 mutant showed only 1-2% adherence capability compared to wild-type C. jejuni, along with reduced biofilm formation and mouse intestinal colonization ability .

What are the most significant technical challenges in working with recombinant C. jejuni atpE?

Working with recombinant C. jejuni atpE presents several significant technical challenges that researchers must address:

• Membrane protein solubility issues:

  • atpE is highly hydrophobic with multiple transmembrane domains

  • Requires careful detergent selection for solubilization

  • Risk of protein aggregation during purification and handling

  • Necessity to maintain detergent above critical micelle concentration throughout all procedures

• Expression optimization difficulties:

  • Potential toxicity to host cells when overexpressed

  • Achieving proper membrane insertion in heterologous hosts

  • Balancing expression levels with proper folding

  • Selection of appropriate host strain and growth conditions

• Structural characterization challenges:

  • Difficulty in obtaining crystals for X-ray crystallography

  • Challenges in obtaining sufficient quantities for NMR studies

  • Need for specialized methods like lipidic cubic phase crystallization or cryo-EM

  • Maintaining native structure in detergent micelles

• Functional assessment limitations:

  • Complexity of reconstituting functional ATP synthase complexes

  • Difficulty separating atpE function from other ATP synthase components

  • Challenges in membrane reconstitution for functional studies

  • Limited availability of C. jejuni-specific assays

• Stability concerns:

  • Protein instability during storage and handling

  • Repeated freeze-thaw cycles significantly reduce activity

  • Need for specialized storage conditions and buffer optimization

  • Short shelf-life of working solutions (approximately one week at 4°C)