Recombinant Bartonella tribocorum ATP synthase subunit a (atpB)

What is the basic structure and function of Bartonella tribocorum ATP synthase subunit a (atpB)?

ATP synthase subunit a (atpB) from Bartonella tribocorum is a component of the F0 sector of ATP synthase, functioning as part of the membrane-embedded proton channel. The recombinant form consists of 252 amino acids with a molecular weight of approximately 27-30 kDa (depending on the tag) . The protein contains multiple transmembrane domains that facilitate proton translocation across the membrane, which is essential for the rotary mechanism of ATP synthesis.

The functional protein adopts a predominantly alpha-helical structure spanning the membrane, with its N-terminus facing the periplasm and C-terminus in the cytoplasm. The amino acid sequence contains highly conserved residues essential for proton translocation, particularly arginine residues that participate in the proton transfer mechanism.

How does atpB from Bartonella tribocorum differ from other bacterial ATP synthase subunits?

Bartonella tribocorum atpB shares structural homology with ATP synthase subunit a from other bacteria, but with several distinguishing features:

The sequence differences reflect evolutionary adaptations to the specific physiological conditions encountered by Bartonella during its complex life cycle involving mammalian hosts and arthropod vectors . These adaptations may include modifications that optimize ATP synthase function at different temperatures and pH conditions encountered during host switching.

What is the significance of studying atpB in the context of Bartonella pathogenesis?

Investigating atpB from Bartonella tribocorum provides insights into energy metabolism during different stages of infection. As Bartonella species are adapted to diverse mammalian hosts, including humans, cats, dogs, and rodents , the energy production mechanisms are critical for understanding bacterial persistence.

ATP synthase is essential for bacterial survival, making it a potential therapeutic target. The protein functions under the varied conditions Bartonella encounters during its life cycle - from arthropod vectors (fleas, ticks) to mammalian bloodstream and endothelial cells . Understanding how atpB contributes to energy homeostasis during these transitions can reveal adaptations that enable host-specific colonization.

Moreover, as Bartonella infections are increasingly linked to a wide spectrum of clinical manifestations beyond the well-known cat-scratch disease, including endocarditis, neurological disorders, and potential links to tumors , understanding fundamental energy metabolism components becomes relevant for comprehending bacterial persistence and pathogenicity.

What are the optimal conditions for expressing and purifying recombinant Bartonella tribocorum atpB?

The expression and purification of membrane proteins like atpB require specific methodological considerations:

Expression System: The recombinant protein is typically expressed in E. coli systems , with BL21(DE3) or similar strains being suitable hosts. For membrane proteins like atpB, C41(DE3) or C43(DE3) strains may provide better results due to their adaptation for membrane protein expression.

Expression Protocol:

• Transform expression plasmid into appropriate E. coli strain

• Culture in LB medium with appropriate antibiotic selection

• Induce with 0.5-1.0 mM IPTG when OD600 reaches 0.6-0.8

• Optimize induction conditions: lower temperature (16-20°C) for 16-20 hours often improves membrane protein folding

• Harvest cells by centrifugation (5,000 × g, 15 min, 4°C)

Purification Approach:

• Resuspend cell pellet in lysis buffer containing detergents (e.g., n-dodecyl-β-D-maltoside or CHAPS)

• Disrupt cells via sonication or high-pressure homogenization

• Perform Ni-NTA affinity chromatography using the His-tag

• Consider size exclusion chromatography as a polishing step

• Maintain detergent throughout purification to prevent protein aggregation

For research applications requiring functional protein, assess protein quality using circular dichroism to confirm secondary structure integrity and thermal stability analysis to evaluate proper folding.

How should researchers reconstitute lyophilized recombinant atpB protein for experimental use?

Proper reconstitution is critical for maintaining protein activity. The methodological approach should include:

• Centrifuge the vial briefly before opening to collect all material at the bottom

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

• For membrane proteins like atpB, consider adding a mild detergent (0.1% n-dodecyl-β-D-maltoside) to maintain solubility

• Gently rotate or invert the vial rather than vortexing to prevent protein denaturation

• Allow complete rehydration by incubating at 4°C for 30-60 minutes

• For long-term storage, add glycerol to a final concentration of 20-50%

• Aliquot to avoid repeated freeze-thaw cycles

• Store at -20°C/-80°C for long-term storage, or at 4°C for up to one week for active use

For functional studies, reconstitution into liposomes may be necessary:

• Prepare lipid mixture mimicking bacterial membrane composition

• Form liposomes through detergent dialysis or extrusion

• Incorporate detergent-solubilized atpB protein during liposome formation

• Remove detergent using Bio-Beads or dialysis

• Verify incorporation using freeze-fracture electron microscopy or functional assays

What analytical methods are most appropriate for verifying the structural integrity of recombinant atpB protein?

Multiple complementary techniques should be employed to comprehensively assess protein structural integrity:

Primary Structure Verification:

• Mass spectrometry (LC-MS/MS) for sequence confirmation and post-translational modification identification

• N-terminal sequencing to confirm correct processing

• SDS-PAGE for molecular weight confirmation (greater than 90% purity should be observed)

Secondary/Tertiary Structure Analysis:

• Circular dichroism (CD) spectroscopy to assess alpha-helical content (expected to be high for atpB)

• Thermal shift assays to evaluate stability

• Limited proteolysis to verify proper folding

• Intrinsic tryptophan fluorescence to monitor tertiary structure

Quaternary Structure Assessment:

• Blue-native PAGE to evaluate oligomeric state

• Analytical ultracentrifugation to determine complex formation

• Size-exclusion chromatography coupled with multi-angle light scattering (SEC-MALS)

Functional Verification:

• ATP hydrolysis assays (reverse direction activity)

• Proton pumping assays in reconstituted liposomes using pH-sensitive dyes

• Binding assays with known interaction partners from the ATP synthase complex

These methods in combination provide comprehensive validation of the recombinant protein's structural and functional integrity before proceeding to more complex experiments.

How can recombinant atpB be utilized to study the bioenergetics of Bartonella during host adaptation?

Investigating the bioenergetics of Bartonella during host adaptation requires sophisticated experimental approaches:

Comparative Bioenergetic Profiling:

• Isolate native ATP synthase complexes from Bartonella cultivated under conditions mimicking different host environments (varying pH, temperature, oxygen levels)

• Incorporate recombinant atpB into ATP synthase complexes lacking the endogenous subunit

• Measure ATP synthesis rates using luciferase-based assays

• Determine proton translocation efficiency using pH-sensitive fluorescent probes

• Compare kinetic parameters (Km, Vmax) under different conditions

Host-Specific Adaptation Studies:
Since Bartonella species have undergone parallel adaptive radiations to colonize different mammalian hosts , researchers can:

• Compare atpB sequences from Bartonella species adapted to different hosts

• Generate chimeric proteins with domains from different species

• Evaluate functional changes using reconstituted systems

• Correlate differences with specific host-adaptive traits

Metabolic Flux Analysis:

• Use stable isotope-labeled metabolites to trace energy utilization pathways

• Compare wild-type and atpB-mutant strains to identify compensatory metabolic shifts

• Develop computational models of Bartonella bioenergetics during host transitions

These approaches allow researchers to understand how ATP synthase components like atpB contribute to the remarkable adaptability of Bartonella across diverse host environments.

What structural biology approaches would be most informative for studying atpB interactions within the ATP synthase complex?

Several structural biology methods can provide valuable insights into atpB interactions:

Cryo-Electron Microscopy:

• Purify intact ATP synthase complexes containing the recombinant atpB

• Perform single-particle cryo-EM analysis to visualize the entire complex

• Focus on the membrane-embedded F0 domain to determine atpB positioning

• Generate 3D reconstructions at sub-4Å resolution to identify interaction interfaces

Cross-linking Mass Spectrometry:

• Apply chemical cross-linkers to stabilize transient interactions

• Digest cross-linked complexes and identify linked peptides by mass spectrometry

• Map interaction sites between atpB and other subunits

• Validate findings using targeted mutagenesis of interaction residues

Molecular Dynamics Simulations:

• Construct atomic models of the Bartonella ATP synthase embedded in a lipid bilayer

• Perform extended (>1 μs) simulations to capture conformational dynamics

• Analyze proton translocation pathways through the a-subunit channel

• Investigate lipid-protein interactions that may be specific to Bartonella

Hydrogen-Deuterium Exchange Mass Spectrometry:

• Monitor solvent accessibility changes upon complex formation

• Identify regions of atpB that become protected in the assembled complex

• Map conformational changes associated with different functional states

These complementary approaches provide multi-scale structural insights that can be integrated to understand the functional architecture of the ATP synthase complex.

How does atpB contribute to Bartonella's adaptation to different mammalian hosts and transmission vectors?

Bartonella species display remarkable host specialization, having undergone parallel adaptive radiations to colonize different mammalian hosts . The ATP synthase, including atpB, likely plays a critical role in this adaptation process:

Comparative Genomic Approaches:

• Analyze atpB sequence variations across Bartonella species with different host preferences

• Identify positive selection signatures in atpB sequences that correlate with host-switching events

• Compare with homologs from other alpha-proteobacteria to identify Bartonella-specific adaptations

Functional Studies Across Physiological Ranges:

• Characterize ATP synthase activity across temperatures ranging from arthropod vector (20-25°C) to mammalian host (37-42°C)

• Evaluate pH sensitivity corresponding to microenvironments encountered during infection

• Investigate oxygen dependence reflecting transition between aerobic and microaerophilic niches

Host-Pathogen Interaction Models:
Bartonella species interact with diverse hosts including cats, dogs, rodents, and humans . Researchers can:

• Establish cell culture models representing different host species

• Compare metabolic activity of wild-type and atpB-mutant Bartonella strains

• Determine if atpB variants show host-specific functional optimization

• Investigate potential interactions between ATP synthase components and host immunity

By understanding how fundamental components like atpB contribute to bioenergetic flexibility, researchers can gain insights into the remarkable adaptability of Bartonella across diverse ecological niches.

How does Bartonella tribocorum atpB compare to ATP synthase components in other bacterial pathogens?

A comparative analysis reveals important similarities and differences:

What insights can be gained by comparing ATP synthase subunits across different Bartonella species?

Comparing ATP synthase components across the Bartonella genus offers insights into evolutionary adaptations:

Evolutionary Conservation Analysis:
Bartonella has undergone parallel adaptive radiations in its evolution , allowing comparisons between:

• Ancestral species (B. bacilliformis) vs. more recently evolved lineages

• Species adapted to different mammalian reservoirs (feline, canine, rodent, human)

• Species with different arthropod vectors (sand flies, fleas, lice, ticks)

Functional Divergence Assessment:

• Identify lineage-specific variations in catalytic residues

• Map sequence differences to structural models

• Correlate with metabolic differences between species

Host Adaptation Signatures:
Researchers can investigate whether ATP synthase components show signatures of selection pressure related to host adaptation, similar to the documented evolutionary patterns in Bartonella's Type IV secretion systems . This can reveal whether energy metabolism components have co-evolved with virulence systems during host adaptation processes.

Such comparative analyses can illuminate how fundamental cellular processes like energy metabolism have been shaped by the ecological specialization of different Bartonella species.

How does the structure-function relationship of atpB differ between Bartonella and model organisms like E. coli?

Understanding the structure-function differences between Bartonella tribocorum atpB and well-characterized model systems provides valuable research context:

Structural Comparison:

• E. coli atpB is the most well-characterized through high-resolution structures

• Bartonella atpB likely maintains the core fold but with species-specific surface features

• Differences in transmembrane helix packing may affect proton conductance properties

• Interface regions with other subunits may show adaptations specific to Bartonella ATP synthase architecture

Functional Parameter Comparison:

Regulatory Differences:

• Expression regulation under stress conditions may differ significantly

• Post-translational modifications may play different roles

• Protein-protein interactions within the complex may show species-specific features

These differences reflect the specialized niche of Bartonella as an intracellular pathogen compared to the more versatile lifestyle of E. coli, potentially providing insights into adaptation mechanisms.

What are the common challenges in working with recombinant atpB and how can they be addressed?

Researchers commonly encounter several challenges when working with membrane proteins like atpB:

Solubility and Aggregation Issues:

• Challenge: atpB is highly hydrophobic and prone to aggregation
  Solution: Screen multiple detergents (DDM, LMNG, CHAPS) at various concentrations; consider adding stabilizing agents like glycerol (6-10%) or specific lipids

• Challenge: Protein precipitation during concentration
  Solution: Maintain detergent above CMC; use centricon filters with 50-100 kDa cutoff to avoid detergent concentration; add mild solubilizing agents

Expression Optimization:

• Challenge: Low expression levels in standard systems
  Solution: Try specialized strains (C41/C43); lower induction temperature (16-20°C); consider fusion partners (MBP, SUMO); optimize codon usage for E. coli

• Challenge: Formation of inclusion bodies
  Solution: Reduce expression rate with lower IPTG concentrations (0.1-0.5 mM); co-express with chaperones; consider refolding protocols

Functional Characterization:

• Challenge: Difficulty assessing activity outside the complete ATP synthase complex
  Solution: Develop partial complex reconstitution systems; use indirect assays such as binding studies with other subunits; employ proteoliposome-based assays

• Challenge: Distinguishing specific activity from background
  Solution: Include appropriate controls (denatured protein, known inactive mutants); perform inhibitor studies; validate with multiple assay types

Storage Stability:

• Challenge: Activity loss during storage
  Solution: Add trehalose (6%) as a stabilizing agent; store in appropriate buffer conditions (pH 8.0 Tris/PBS-based buffer) ; avoid repeated freeze-thaw cycles by preparing single-use aliquots

How can researchers validate that recombinant atpB retains native-like structure and function?

Comprehensive validation requires multiple complementary approaches:

Structural Validation:

Functional Validation:

• Subunit binding assays to verify interaction with partner proteins from the ATP synthase complex

• Proton translocation assays in reconstituted proteoliposomes using pH-sensitive fluorescent dyes

• ATP hydrolysis complementation studies in which recombinant atpB restores activity to deficient complexes

• Inhibitor binding studies using known ATP synthase inhibitors

Comparative Validation:

• Parallel characterization of E. coli atpB as a reference standard

• Comparison with native Bartonella ATP synthase purified from cultured bacteria

• Cross-validation using multiple experimental techniques

Biological Relevance Assessment:

• Complementation studies in bacterial mutants lacking functional atpB

• Structure-guided mutagenesis of key residues with functional testing

• Correlation of biochemical properties with physiological conditions encountered during infection

This multi-faceted validation approach ensures that experimental findings with the recombinant protein accurately reflect the biological properties of native atpB.

A5.3. What experimental controls are essential when studying the role of atpB in Bartonella physiology?

Genetic Controls:

• Clean deletion mutants (ΔatpB) with confirmed genotype

• Complemented strains expressing wild-type atpB from a plasmid or chromosomal integration

• Point mutants affecting specific functions (e.g., proton channel function) rather than structure

• Strains with tagged versions of atpB to control for tag effects

Biochemical Controls:

• Heat-inactivated protein preparations to distinguish enzymatic from non-enzymatic effects

• Known ATP synthase inhibitors as positive controls for inhibition studies

• Purified E. coli ATP synthase components as reference standards

• Isotopically labeled controls for mass spectrometry experiments

Physiological Controls:

• Growth under various energy source conditions to distinguish ATP synthase-dependent effects

• Oxygen limitation experiments with appropriate aerobic and anaerobic controls

• pH-controlled experiments with buffer controls

• Temperature variation with appropriate adaptation periods

Infection Model Controls:

• Non-pathogenic Bartonella species or related alpha-proteobacteria

• Host cell controls (uninfected, treated with purified components)

• Time-course studies to distinguish early from late effects

• Multiple cell types representing different host environments

Implementing these controls enables researchers to confidently attribute observed phenotypes to specific aspects of atpB function rather than experimental artifacts or secondary effects.

How might atpB serve as a target for developing novel therapeutics against Bartonella infections?

ATP synthase represents a promising but challenging therapeutic target. Several research avenues merit exploration:

Structure-Based Inhibitor Design:

• Determine high-resolution structures of Bartonella ATP synthase with focus on atpB

• Identify unique structural features that distinguish it from mammalian ATP synthase

• Design small molecules targeting the proton channel formed by atpB

• Perform virtual screening followed by experimental validation

Existing ATP Synthase Inhibitors:

• Evaluate efficacy of known inhibitors (oligomycin, venturicidin, diarylquinolines)

• Optimize selectivity for bacterial versus mammalian ATP synthase

• Assess synergy with existing antibiotics used against Bartonella (doxycycline, rifampin)

Peptide-Based Approaches:

• Design peptides that disrupt crucial protein-protein interactions within the ATP synthase complex

• Develop cell-penetrating peptides targeting the cytoplasmic interface of atpB

• Engineer phage display libraries to identify specific binders

Delivery Strategies:
Since Bartonella is an intracellular pathogen , effective therapies require appropriate delivery systems:

• Liposomal formulations to enhance cellular uptake

• Nanoparticle carriers with targeting moieties

• Prodrug approaches leveraging bacterial metabolism

Therapeutic development must consider the complex lifecycle of Bartonella, including persistent infections and the potential for metabolic dormancy during chronic infections. Combination approaches targeting energy metabolism alongside other essential pathways may prove most effective for eradicating persistent infections.

What role might atpB play in the adaptation of Bartonella to new host species?

Understanding atpB's role in host adaptation could provide insights into Bartonella's evolutionary history and emergence as a pathogen:

Evolutionary Analysis:

• Compare atpB sequences across Bartonella species that infect different host species

• Identify signatures of positive selection that correlate with host-switching events

• Conduct ancestral sequence reconstruction to track evolutionary trajectories

• Map adaptive mutations onto structural models to predict functional consequences

Host-Specific Functional Studies:

• Express and characterize atpB variants from Bartonella species adapted to different hosts

• Assess functionality under conditions mimicking different host environments

• Perform reciprocal gene replacement experiments between species

• Monitor bacterial fitness in different host cell models

Parallel Evolution Analysis:
Bartonella has undergone parallel adaptive radiations , making it an excellent model to study convergent evolution. Researchers could:

• Compare atpB adaptations with other Bartonella systems showing adaptive evolution

• Determine if energy metabolism components co-evolved with virulence factors

• Investigate whether similar modifications occurred independently in different lineages

Transmission Cycle Considerations:
Since Bartonella cycles between arthropod vectors and mammalian hosts , researchers should:

• Characterize atpB function across relevant temperature ranges (20-40°C)

• Assess activity under varying oxygen tensions and pH conditions

• Determine if atpB variants show specialized adaptation to particular vector-host combinations

This research could illuminate fundamental aspects of pathogen adaptation and host range determination.

How does ATP synthase function integrate with other Bartonella virulence systems during infection?

The relationship between energy metabolism and virulence deserves systematic investigation:

Interaction with Type IV Secretion Systems:
Bartonella species possess multiple T4SSs (VirB, Vbh, Trw) that are crucial for host interaction. Researchers should explore:

• Energetic requirements for T4SS assembly and function

• Co-regulation of ATP synthase and T4SS genes during infection

• Physical interactions between ATP synthase components and T4SS machinery

• Effects of ATP synthase inhibition on secretion system function

Metabolic Adaptation During Infection Stages:

• Profile ATP synthase activity during different phases of infection

• Investigate metabolic remodeling upon host cell invasion

• Determine if ATP synthase undergoes composition changes during chronic infection

• Assess the role of atpB in supporting long-term persistence

Integration with Stress Responses:

• Characterize the relationship between energy production and stress adaptation

• Investigate whether ATP synthase components participate in stress signaling

• Determine how nutrient limitation affects ATP synthase function and composition

• Explore potential moonlighting functions of atpB beyond ATP synthesis

System-Level Analysis:

• Perform transcriptomic analysis comparing wild-type and atpB mutants during infection

• Use metabolomics to map energy flux changes

• Develop computational models integrating ATP production with virulence factor expression

• Employ interactome studies to identify non-canonical interaction partners

Understanding these integrated functions could reveal novel intervention points that simultaneously target energy production and virulence, potentially overcoming adaptive resistance mechanisms.