Recombinant Campylobacter fetus subsp. fetus ATP synthase subunit c (atpE)

What is the composition and structure of Recombinant Campylobacter fetus subsp. fetus ATP synthase subunit c (atpE)?

The Recombinant Campylobacter fetus subsp. fetus ATP synthase subunit c (atpE) is a full-length protein (1-100 amino acids) that is typically expressed with an N-terminal His tag in E. coli expression systems. The amino acid sequence of this protein is: MKKVLFLVVALASFAFGADGEQIKAFSVVAAGIGLGVAALGGAIGMGHTAAATILGTARNPGLGGKLLTTMFIALAMIEAQVIYALVIALIALYANPFLG. The protein forms part of the F0 sector of ATP synthase and functions as a lipid-binding protein. The recombinant form is typically supplied as a lyophilized powder with greater than 90% purity as determined by SDS-PAGE .

What are the optimal storage and reconstitution conditions for recombinant atpE protein?

For optimal stability, the recombinant atpE protein should be stored at -20°C to -80°C upon receipt, with aliquoting recommended for multiple uses to avoid repeated freeze-thaw cycles. The protein is typically supplied in a Tris/PBS-based buffer with 6% trehalose at pH 8.0. For reconstitution:

• Centrifuge the vial briefly before opening

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

• Add glycerol to a final concentration of 5-50% (50% is standard)

• Aliquot for long-term storage at -20°C/-80°C

• Working aliquots can be stored at 4°C for up to one week

Repeated freeze-thaw cycles should be avoided as they may lead to protein degradation and loss of activity.

How does Campylobacter fetus differ across its subspecies, and what implications does this have for atpE research?

Campylobacter fetus comprises three recognized subspecies with distinct host associations:

Despite conservation of gene content and organization among these subspecies, clear genetic distinctions exist between mammal-associated and reptile-associated C. fetus. When working with atpE from different subspecies, researchers should consider these genomic differences as they may influence protein structure, function, and expression systems .

What methodologies are most effective for studying the functional role of atpE in Campylobacter fetus subsp. fetus?

To effectively study the functional role of atpE in C. fetus subsp. fetus, a multi-methodological approach is recommended:

• Genetic manipulation: Create knockout mutants using methods like allelic exchange to assess the phenotypic effects of atpE deletion.

• Protein expression and purification: Express the recombinant protein with affinity tags for purification and subsequent functional studies.

• Structural analysis: Employ techniques such as X-ray crystallography or cryo-electron microscopy to determine the protein structure.

• Protein-protein interaction studies: Use pull-down assays, co-immunoprecipitation, or yeast two-hybrid systems to identify interaction partners within the ATP synthase complex.

• Enzymatic assays: Develop in vitro assays to measure ATP synthase activity with and without functional atpE.

• Comparative genomics: Compare atpE sequences across C. fetus subspecies to identify conserved regions and subspecies-specific variations that might correlate with functional differences .

When designing these experiments, researchers should consider the distinct genomic features of C. fetus subspecies, which could influence the function and regulation of atpE in different host environments.

How can recombinant atpE be utilized in studying the pathogenicity of Campylobacter fetus subsp. fetus?

The recombinant atpE protein can serve as a valuable tool in investigating C. fetus pathogenicity through several approaches:

• Immunogenicity studies: Determine whether atpE elicits an immune response in host organisms and whether antibodies against atpE provide protection against infection.

• Biofilm formation analysis: Investigate the role of atpE in biofilm formation, which may contribute to bacterial persistence.

• Host-pathogen interaction models: Use recombinant atpE to study interactions with host cell components, potentially identifying receptors or cellular targets.

• Metabolic adaptation studies: Examine how atpE function relates to C. fetus adaptation to different host environments, considering that ATP synthase is crucial for energy metabolism.

• Virulence factor correlation: Determine whether atpE expression correlates with other known virulence factors like the S-layer proteins (SLPs), which mediate serum resistance and are critical for C. fetus virulence .

Research indicates that the S-layer of C. fetus inhibits binding of complement factor C3b, resulting in resistance to phagocytosis and complement-mediated killing. While atpE is not directly a part of this system, energy provision through ATP synthesis may be essential for maintaining these virulence mechanisms .

How does the secretion of surface layer proteins in Campylobacter fetus relate to ATP synthase components like atpE?

The relationship between surface layer proteins (SLPs) and ATP synthase components involves several complex interactions:

• Energy requirements: The type I secretion system for SLPs (encoded by sapCDEF genes) requires energy in the form of ATP, which is produced by ATP synthase complexes containing atpE.

• Membrane localization: Both the F0 sector of ATP synthase (containing atpE) and components of the SLP secretion system are membrane-associated, suggesting potential spatial relationships or membrane domain preferences.

• Regulatory networks: Expression of both systems may be co-regulated under certain environmental conditions, particularly during host infection or stress response.

The secretion of SLPs in C. fetus occurs through a type I secretion system encoded by the sapCDEF genes. This system functions without an N-terminal signal sequence, instead utilizing C-terminal secretion signals. Analysis has shown that SapD, SapE, and SapF have predicted amino acid homologies with type I protein secretion systems from other bacterial species .

A potential model for the interaction between these systems is that ATP generated by the ATP synthase (containing atpE) provides the energy required for the active transport of SLPs across the cell membrane via the SapCDEF system. This relationship highlights the importance of energy metabolism in virulence factor expression and secretion.

What are the methodological challenges in expressing and purifying functional recombinant atpE, and how can these be addressed?

Several methodological challenges exist in the expression and purification of functional recombinant atpE:

Experimental data from successful expression systems indicates that using an N-terminal His tag and expressing the protein in E. coli can yield pure protein (>90% purity by SDS-PAGE), but researchers must carefully optimize conditions based on their specific experimental requirements .

How can multilocus sequence typing (MLST) and other molecular techniques be applied to study genetic variation in the atpE gene across Campylobacter fetus isolates?

MLST and other molecular techniques can be effectively applied to study genetic variation in the atpE gene through the following methodologies:

Data from comparative genomics studies have revealed conservation of gene content and organization among C. fetus subspecies, but clear distinctions between mammal- and reptile-associated strains. This suggests that while atpE may be conserved functionally, there could be subspecies-specific variations that reflect adaptation to different host environments .

What experimental controls should be included when working with recombinant Campylobacter fetus subsp. fetus atpE protein?

When designing experiments with recombinant C. fetus subsp. fetus atpE protein, the following controls should be incorporated:

• Positive controls:

  • Commercially available ATP synthase components with known activity

  • Previously validated batches of recombinant atpE protein

  • Native C. fetus membrane preparations containing the complete ATP synthase complex

• Negative controls:

  • Heat-denatured atpE protein to confirm activity is dependent on proper protein folding

  • Buffer-only samples without protein

  • Expression product from empty vector transformants

• Specificity controls:

  • Homologous proteins from related species (e.g., C. jejuni or E. coli ATP synthase subunit c)

  • Other C. fetus membrane proteins not involved in ATP synthesis

  • Antibodies pre-absorbed with purified antigen (for immunological studies)

• Technical controls:

  • Different concentrations of the recombinant protein to establish dose-dependency

  • Time-course experiments to determine optimal reaction times

  • Alternative tag systems (beyond His tag) to ensure tags don't interfere with function

• Biological relevance controls:

  • Comparisons with wild-type C. fetus strains

  • atpE knockout mutants for complementation studies

  • Growth under different environmental conditions to mimic in vivo settings

Implementing these controls helps validate experimental findings and ensures that observed effects are specifically attributable to the atpE protein rather than experimental artifacts or contamination .

How can researchers investigate the interaction between atpE and other components of the ATP synthase complex in Campylobacter fetus?

Investigating protein-protein interactions within the ATP synthase complex requires a multi-faceted approach:

• Co-immunoprecipitation (Co-IP):

  • Use antibodies against tagged recombinant atpE to pull down associated proteins

  • Identify interaction partners through mass spectrometry

  • Confirm specificity using reciprocal Co-IP with antibodies against putative partners

• Bacterial two-hybrid systems:

  • Generate fusion constructs of atpE and other ATP synthase components

  • Screen for interactions based on reporter gene activation

  • Quantify interaction strength through dose-response experiments

• Surface plasmon resonance (SPR):

  • Immobilize purified atpE on sensor chips

  • Measure binding kinetics with other purified ATP synthase components

  • Determine affinity constants for different protein-protein interactions

• Crosslinking studies:

  • Use chemical crosslinkers to stabilize transient interactions in vivo

  • Identify crosslinked complexes through gel electrophoresis and mass spectrometry

  • Map interaction interfaces based on crosslinked residues

• Structural biology approaches:

  • Cryo-electron microscopy of reconstituted ATP synthase complexes

  • X-ray crystallography of atpE in complex with interaction partners

  • NMR studies of labeled atpE to identify binding interfaces

• Computational modeling:

  • Predict interaction interfaces based on homology to known ATP synthase structures

  • Molecular dynamics simulations to study dynamic interactions

  • Docking studies to predict binding modes

By combining these methodologies, researchers can build a comprehensive understanding of how atpE integrates into the larger ATP synthase complex in C. fetus, potentially identifying subspecies-specific interactions that might relate to adaptation to different host environments .

How should researchers interpret comparative genomics data when studying atpE variation across Campylobacter species and subspecies?

When interpreting comparative genomics data for atpE across Campylobacter species and subspecies, researchers should consider:

• Sequence conservation analysis:

  • Calculate percent identity and similarity at nucleotide and amino acid levels

  • Identify highly conserved regions that may be functionally essential

  • Map variation to specific domains or structural elements

• Phylogenetic context:

  • Construct phylogenetic trees based on atpE sequences

  • Compare atpE-based phylogeny with whole-genome or MLST-based phylogenies

  • Assess whether atpE evolution follows species evolution or shows evidence of horizontal gene transfer

• Selection pressure analysis:

  • Calculate dN/dS ratios to determine whether atpE is under purifying, neutral, or positive selection

  • Identify specific codons under different selection pressures

  • Compare selection pressures across different host-associated lineages

• Host adaptation signatures:

  • Look for consistent differences between mammal-associated and reptile-associated C. fetus

  • Correlate specific variations with host-specific environmental factors

  • Consider coevolution with other genes in the ATP synthase complex

• Functional implications:

  • Use structural modeling to predict how variations might affect protein function

  • Consider how changes might influence proton translocation or complex assembly

  • Evaluate potential impacts on ATP synthesis efficiency in different host environments

Research has shown that C. fetus subspecies display distinct host associations, with C. fetus subsp. fetus and C. fetus subsp. venerealis primarily associated with mammals, while C. fetus subsp. testudinum is primarily associated with reptiles. These divergent lineages show evidence of allopatric speciation with barriers to lateral gene transfer between mammal- and reptile-associated strains .

When interpreting genomic data, consider that these host-specific adaptations may extend to energy metabolism genes like atpE, potentially reflecting adaptation to different temperature regimes or metabolic environments in mammalian versus reptilian hosts.

What statistical approaches are most appropriate for analyzing functional data related to recombinant atpE activity?

When analyzing functional data for recombinant atpE, the following statistical approaches are recommended:

• For enzymatic activity measurements:

  • Michaelis-Menten kinetics analysis to determine Km and Vmax parameters

  • Analysis of variance (ANOVA) to compare activity across different experimental conditions

  • Non-linear regression for fitting dose-response curves

  • Time-series analysis for measuring activity over time

• For protein-protein interaction studies:

  • Binding curve analysis to determine dissociation constants (Kd)

  • Scatchard plot analysis for multiple binding site evaluation

  • Statistical tests for co-localization in microscopy studies (Pearson's correlation, Manders' overlap coefficient)

• For structural stability experiments:

  • Thermal shift assay data analysis (determination of melting temperature)

  • Circular dichroism spectroscopy data interpretation for secondary structure content

  • Principal component analysis (PCA) for structural variant clustering

• For comparative experiments:

  • Student's t-test (paired or unpaired depending on experimental design)

  • ANOVA with post-hoc tests (Tukey's, Bonferroni, etc.) for multiple condition comparisons

  • Non-parametric alternatives (Mann-Whitney U, Kruskal-Wallis) for non-normally distributed data

• For reproducibility assessment:

  • Calculation of coefficient of variation (CV) across technical and biological replicates

  • Intraclass correlation coefficient (ICC) for reliability analysis

  • Power analysis to determine appropriate sample sizes

• Data visualization techniques:

  • Box plots for distribution visualization

  • Heat maps for multivariate data presentation

  • Forest plots for meta-analysis of multiple studies

When reporting results, include both the effect size and statistical significance, with appropriate correction for multiple comparisons when necessary. Sample sizes, p-values, confidence intervals, and specific statistical tests used should be clearly stated to allow for proper interpretation and reproducibility of findings.

What are the common challenges in expressing recombinant Campylobacter fetus subsp. fetus atpE protein, and how can they be resolved?

Researchers frequently encounter several challenges when expressing recombinant C. fetus subsp. fetus atpE protein:

Based on the product information, the recombinant C. fetus atpE protein can be successfully expressed in E. coli with an N-terminal His tag and purified to >90% purity. For optimal results, the protein should be stored as a lyophilized powder and reconstituted according to the recommended protocol in a Tris/PBS-based buffer with 6% trehalose at pH 8.0 .

How can researchers troubleshoot unexpected experimental results when working with atpE in Campylobacter fetus pathogenicity studies?

When troubleshooting unexpected results in C. fetus atpE pathogenicity studies, researchers should follow this systematic approach:

• Validate reagent quality and identity:

  • Confirm protein purity by running fresh SDS-PAGE

  • Verify protein identity using mass spectrometry or western blotting

  • Check for contamination with endotoxins that might affect host cell responses

  • Ensure proper storage conditions have been maintained

• Review experimental design:

  • Reassess control selections and validate their performance

  • Confirm that cell lines or animal models are appropriate for C. fetus studies

  • Evaluate whether experimental conditions mimic physiological relevance

  • Consider time-dependent effects that might have been overlooked

• Analyze technical execution:

  • Review all protocol steps for deviations or errors

  • Calibrate and validate equipment (incubators, plate readers, etc.)

  • Assess reagent compatibility and potential interactions

  • Consider operator variability if multiple researchers are involved

• Investigate biological complexity:

  • Consider host cell factors that might influence results

  • Evaluate potential compensatory mechanisms in knockout studies

  • Assess whether the unexpected results reveal novel biology

  • Review literature for similar paradoxical findings with related proteins

• Confirm reproducibility:

  • Repeat experiments with increased sample sizes

  • Test across different batches of reagents and cell preparations

  • Consider blind experimental design to eliminate bias

  • Implement alternative methodological approaches to test the same hypothesis

• Contextual considerations:

  • Compare with other subspecies of C. fetus to identify subspecies-specific effects

  • Consider the impact of the S-layer, which is known to be important for C. fetus virulence

  • Evaluate potential interactions between atpE and other virulence factors

This systematic approach can help determine whether unexpected results represent technical issues, experimental design flaws, or genuine novel biological findings. The complex host-pathogen interactions in C. fetus infections, particularly the role of the S-layer in serum resistance and immune evasion, might interact with energy metabolism in ways that produce unexpected experimental outcomes .

What are the emerging research areas related to Campylobacter fetus subsp. fetus ATP synthase components in pathogenesis and antimicrobial resistance?

Several promising research directions are emerging at the intersection of ATP synthase biology and C. fetus pathogenesis:

• ATP synthase as a drug target:

  • Investigation of atpE and other ATP synthase components as targets for novel antimicrobials

  • Screening of compounds that specifically inhibit C. fetus ATP synthase

  • Development of structure-based drug design approaches targeting unique features of C. fetus atpE

• Metabolic adaptation during infection:

  • Characterization of ATP synthase regulation during different stages of infection

  • Investigation of how C. fetus modulates energy metabolism in different host environments

  • Exploration of potential metabolic bottlenecks that could be exploited therapeutically

• Host-specific adaptations:

  • Comparative analysis of ATP synthase components across mammal-associated and reptile-associated strains

  • Investigation of temperature-dependent ATP synthase function across subspecies

  • Evaluation of how host-specific adaptations in energy metabolism contribute to host range

• Antimicrobial resistance mechanisms:

  • Study of how ATP synthase modifications might contribute to antibiotic tolerance

  • Investigation of energy-dependent efflux pump activity

  • Characterization of persister cell formation in relation to ATP levels

• Interplay with virulence factors:

  • Investigation of energy requirements for S-layer protein expression and secretion

  • Study of potential regulatory links between energy status and virulence factor expression

  • Characterization of ATP-dependent processes in host cell invasion and immune evasion

• Vaccine development:

  • Assessment of ATP synthase components as potential vaccine antigens

  • Evaluation of cross-protection potential across C. fetus subspecies

  • Development of attenuated strains with modified ATP synthase for live vaccine candidates

The distinct genetic features of C. fetus subspecies, combined with their host specificity patterns, provide a valuable model system for studying how energy metabolism adapts to different host environments and contributes to pathogenesis. Recent comparative genomics studies highlighting the divergence between mammal- and reptile-associated C. fetus strains suggest that metabolic adaptation plays a key role in host specialization .