Recombinant Bartonella tribocorum ATP synthase subunit b 1 (atpF1)

What is ATP synthase subunit b 1 (atpF1) and its role in Bartonella tribocorum?

ATP synthase subunit b 1 (atpF1) is a critical component of the F0F1-ATP synthase complex in Bartonella species. This membrane-bound protein serves as part of the F0 sector, which forms the proton channel embedded in the bacterial membrane. Based on related species data, B. tribocorum atpF1 likely consists of approximately 188 amino acids with a structure featuring transmembrane regions that anchor the protein in the membrane and cytoplasmic regions that interact with other subunits of the complex . The primary function of atpF1 is to contribute to the structural stability of the ATP synthase complex and participate in the mechanical coupling between proton translocation through F0 and ATP synthesis in F1 .

How does ATP synthase subunit b 1 compare between different Bartonella species?

Comparison between B. quintana and B. henselae atpF1 sequences reveals high similarity with strategic differences:

The sequence of B. quintana atpF1 (MFISSACAQSNEILVEHIKNASEHADRIFPPFDFVHFGSHFFWLAISFGLFYLFISRVIVPRIGDVIETRRDRIASDLDQAMRMKQEADTVVETYERKLAQARSQAHVIAQAAGEEIKQKVELERREIEASLEKKLKDAEKQIAKIRDKAMQNVGSIAEEAALEIVKKMIDVDVSRESAVKAAGY) differs from B. henselae atpF1 (MFISSAYAQNTETSLEHIKNVAERIDRVFPPFDFVHFGSHLFWLAISFGLFYLFISRVIVPRIGGVIETRRDRIASDLDQAMRMKQEADIVVETYERKLAQARSQAHVIAQTASEEIKQKVELERKEIEANLEKKLTDAEKQIAKIRDKAMKSVGSIAEEVALEIVKKLIDVEVSKESVRSAVKATGY) at approximately 23 positions . These differences may reflect host-specific adaptations, as B. quintana primarily infects humans while B. henselae naturally infects cats.

What is the structural organization of the complete F0F1-ATP synthase in Bartonella species?

The F0F1-ATP synthase in Bartonella species, like in other bacteria, consists of two main sectors:

• F1 sector (soluble): Contains five subunits (α, β, γ, δ, and ε) arranged in a specific stoichiometry (α3β3γδε), forming the catalytic portion responsible for ATP synthesis/hydrolysis.

• F0 sector (membrane-embedded): Contains multiple subunits including subunit b (atpF1), forming the proton channel that harnesses the proton motive force.

The complex functions as a rotary nanomotor where proton flow through F0 drives rotation of the central stalk (γ, ε), causing conformational changes in the catalytic sites of F1 that facilitate ATP synthesis . Electron microscopy studies of bacterial F0F1-ATP synthases reveal a mushroom-like structure with F1 extending into the cytoplasm and F0 embedded in the membrane.

What expression systems are optimal for recombinant Bartonella ATP synthase subunits?

Based on published methodologies, two primary expression systems have proven effective:

E. coli expression system:

• Successfully used for B. quintana and B. henselae atpF1

• Advantages: High yield, cost-effective, rapid expression

• Considerations: Codon optimization may be necessary; inclusion body formation common with membrane proteins

Baculovirus expression system:

• Successfully used for B. tribocorum atpA

• Advantages: Enhanced protein folding, suitable for complex proteins, supports post-translational modifications

• Considerations: Higher cost, longer expression time, more complex methodology

The choice between systems should be guided by the specific research application. For structural studies requiring large protein quantities, E. coli systems with solubility tags may be preferable. For functional studies requiring properly folded proteins, the baculovirus system offers advantages .

What purification strategies yield the highest purity and activity of recombinant atpF1?

A multi-step purification strategy is recommended for optimal results:

• Initial capture: Immobilized metal affinity chromatography (IMAC) using His-tagged constructs

  • Buffer optimization: Include mild detergents (0.05-0.1% DDM or LDAO) to maintain solubility

  • pH range: 7.5-8.0 provides optimal stability

• Intermediate purification: Ion exchange chromatography

  • Removes co-purifying bacterial proteins

  • Can separate different oligomeric states

• Polishing step: Size exclusion chromatography

  • Buffer composition: 20 mM Tris-HCl pH 7.5, 150 mM NaCl, 0.03% DDM

  • Confirms homogeneity and oligomeric state

This approach consistently achieves >90% purity as determined by SDS-PAGE . For functional studies, reconstitution into liposomes or nanodiscs may be necessary to maintain native-like membrane environment.

How should recombinant Bartonella ATP synthase subunits be stored to maintain stability?

Based on established protocols for related proteins, the following storage recommendations apply:

Short-term storage (up to 1 week):

• Temperature: 4°C

• Buffer: Tris/PBS-based buffer with 0.03% detergent

• Avoid repeated freeze-thaw cycles

Long-term storage (months to years):

• Temperature: -20°C/-80°C

• Buffer: Add glycerol to 50% final concentration

• Format: Aliquot in small volumes to avoid freeze-thaw cycles

• Lyophilization: Provides enhanced stability with proper reconstitution protocols

For lyophilized protein, reconstitution should be performed in deionized sterile water to a concentration of 0.1-1.0 mg/mL with brief centrifugation prior to opening the vial .

How does ATP synthase function relate to Bartonella pathogenicity and host adaptation?

ATP synthase plays a crucial role in Bartonella pathogenicity through several mechanisms:

• Energy provision for virulence systems: The VirB/VirD4 Type IV Secretion System (T4SS), a key virulence factor in Bartonella, requires substantial energy for assembly and effector protein translocation. ATP synthase likely provides the necessary energy to fuel this system .

• Adaptation to microenvironments: Bartonella species encounter varying environmental conditions during their infection cycle (arthropod vector, mammalian bloodstream, endothelial cells). The ATP synthase may be differentially regulated to optimize energy production under these diverse conditions .

• pH adaptation mechanisms: The BatR/BatS two-component regulatory system in Bartonella functions optimally at physiological blood pH (7.4), unlike homologous systems in other alphaproteobacteria that are activated at acidic pH . This suggests unique adaptation of Bartonella's energy metabolism to its hemotropic lifestyle.

Research exploring potential connections between ATP synthase regulation and expression of virulence factors could reveal important insights into Bartonella pathogenesis mechanisms.

What experimental approaches can assess ATP synthase functionality in Bartonella?

Several complementary approaches can assess functionality:

In vitro biochemical assays:

• ATP synthesis activity measurement using luciferase-based assays

• ATP hydrolysis activity using colorimetric phosphate detection

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

In vivo functional assessment:

• Gene knock-down/knock-out studies with phenotypic analysis

• Complementation experiments with mutant variants

• Metabolic analysis during infection using 13C-labeled substrates

Structural analysis:

• Blue-native PAGE to assess complex integrity

• Cryo-electron microscopy for structural determination

• Hydrogen-deuterium exchange mass spectrometry for conformational dynamics

A study in trypanosomes demonstrated that RNAi silencing of F1 subunits led to decreased ATP production by oxidative phosphorylation while substrate phosphorylation remained largely unaffected . Similar approaches could be applied to Bartonella to assess ATP synthase function.

How might ATP synthase inhibitors be used to study Bartonella pathogenicity?

ATP synthase inhibitors provide valuable tools for investigating energy metabolism in Bartonella:

Classes of inhibitors with research applications:

• F1 inhibitors (e.g., aurovertin B, efrapeptins)

• F0 inhibitors (e.g., oligomycin, venturicidin)

• Coupling inhibitors (e.g., dicyclohexylcarbodiimide, DCCD)

Research applications:

• Determining ATP synthase essentiality in different infection stages

• Investigating metabolic adaptations to energy limitation

• Exploring connections between energy status and virulence factor expression

Experimental design considerations:

• Use sublethal concentrations to avoid non-specific effects

• Include metabolic rescue controls (e.g., fermentable carbon sources)

• Combine with transcriptomic/proteomic analysis to identify compensatory mechanisms

This approach may reveal whether Bartonella species are sensitive to ATP synthase inhibitors during specific phases of infection, similar to observations in other bacterial pathogens.

How does Bartonella ATP synthase compare to that of other alphaproteobacteria?

Comparative analysis reveals both conserved features and unique adaptations:

The adaptation of regulatory systems like BatR/BatS to function optimally at blood pH (7.4) rather than acidic pH represents a significant evolutionary adaptation to Bartonella's hemotropic lifestyle compared to soil-dwelling relatives like Agrobacterium .

What can be learned from comparing ATP synthase subunit b 1 sequences across Bartonella lineages?

Sequence analysis of atpF1 across Bartonella species provides evolutionary insights:

• Conservation patterns: The transmembrane regions show higher conservation than cytoplasmic regions, reflecting functional constraints on membrane integration.

• Lineage-specific adaptations: Different Bartonella lineages show distinct sequence signatures in atpF1, potentially reflecting adaptation to different mammalian hosts. Bartonella has undergone adaptive radiation with at least two parallel radiations identified through genomic analyses .

• Evolutionary rate: Comparison of synonymous vs. non-synonymous substitution rates in atpF1 could reveal whether this protein is under purifying selection or has undergone adaptive evolution during host-switching events.

Such comparative analyses could provide insights into the co-evolution of Bartonella energy metabolism with host adaptation during the genus's evolutionary history.

What are the main challenges in expressing and purifying functional recombinant atpF1?

Several key challenges and their solutions have been identified:

Challenge 1: Membrane protein solubility

• Solution: Optimize detergent selection (DDM, LDAO, OG) through small-scale screening

• Alternative: Use fusion partners (MBP, SUMO) to enhance solubility

• Consideration: Different detergents may affect protein stability and activity differently

Challenge 2: Proper folding and oligomerization

• Solution: Reduce expression temperature (16-20°C) to slow folding process

• Alternative: Co-express with chaperones (GroEL/ES, DnaK/J/GrpE)

• Validation: Circular dichroism to confirm secondary structure elements

Challenge 3: Functional assessment of isolated subunit

• Solution: Reconstitution into liposomes or nanodiscs

• Alternative: Co-expression with partner subunits to form sub-complexes

• Validation: ATP synthesis/hydrolysis assays in reconstituted systems

Proper handling during purification is crucial, with recommended storage in Tris/PBS-based buffer containing 6% trehalose at pH 8.0 .

How can researchers confirm the structural integrity of purified recombinant atpF1?

Multiple complementary techniques provide comprehensive structural validation:

Spectroscopic methods:

• Circular dichroism (CD): Confirms secondary structure integrity

• Fluorescence spectroscopy: Assesses tertiary structure through intrinsic tryptophan fluorescence

• Fourier-transform infrared spectroscopy (FTIR): Particularly valuable for membrane proteins

Hydrodynamic methods:

• Size-exclusion chromatography with multi-angle light scattering (SEC-MALS): Determines oligomeric state

• Analytical ultracentrifugation: Provides detailed information on size, shape, and homogeneity

Structural stability assays:

• Thermal shift assays: Monitors protein unfolding as a function of temperature

• Limited proteolysis: Identifies flexible vs. protected regions

• Hydrogen-deuterium exchange mass spectrometry: Maps solvent-accessible regions

The combination of these techniques provides comprehensive validation of structural integrity before proceeding to functional studies.

What strategies can overcome expression variability between different batches?

Batch-to-batch consistency can be achieved through standardized protocols:

Expression standardization:

• Maintain consistent cell density at induction (OD600 = 0.6-0.8)

• Control induction temperature precisely (±0.5°C)

• Standardize induction time and harvesting protocols

• Use glycerol stocks from the same master culture

Purification standardization:

• Implement automated chromatography methods

• Utilize in-line quality control (UV, light scattering, refractive index)

• Define acceptance criteria for each purification step

• Perform batch certification using activity assays

Quality control metrics:

• SDS-PAGE purity >90%

• Specific activity within 15% of reference standard

• A260/A280 ratio <0.7 (indicating minimal nucleic acid contamination)

• Endotoxin levels <1 EU/mg protein

Implementation of these strategies has been shown to reduce batch-to-batch variability to <10% for similar recombinant proteins.

How might ATP synthase function intersect with the VirB/VirD4 type IV secretion system?

The relationship between ATP synthase and the VirB/VirD4 T4SS represents an exciting frontier:

• Energy coupling hypothesis: The T4SS requires substantial ATP for assembly and function. Research could investigate if there is preferential channeling of ATP from the synthase to the secretion system through protein-protein interactions or membrane microdomains .

• Co-regulation mechanisms: Both systems may be co-regulated in response to environmental cues. The BatR/BatS system has been shown to regulate VirB/VirD4 expression , but its potential influence on ATP synthase expression remains unexplored.

• Spatial organization: Advanced imaging techniques could reveal whether ATP synthase complexes are spatially arranged near T4SS complexes in the bacterial membrane, potentially forming energy-secretion microdomains.

Experimental approaches might include co-immunoprecipitation studies, proximity labeling techniques (BioID, APEX), and high-resolution microscopy to investigate these potential interactions.

What is the potential role of ATP synthase in Bartonella adaptation to different hosts?

ATP synthase may play a critical role in host adaptation through several mechanisms:

• Host-specific energy optimization: Different mammalian hosts present distinct nutritional environments. ATP synthase regulation may be optimized for the specific carbon sources and oxygen tensions encountered in different host species.

• Temperature adaptation: Bartonella species infect mammals with different body temperatures. The ATP synthase complex may contain structural adaptations that optimize function at the specific temperature of the preferred host.

• Immune evasion strategies: ATP synthase components could potentially be recognized by host immune systems. Sequence variations observed between species might reflect immune evasion adaptations.

Comparative studies examining ATP synthase structure, regulation, and function across Bartonella species that infect different hosts (e.g., B. henselae in cats vs. B. quintana in humans) could reveal host-specific adaptations .

Could ATP synthase components serve as potential diagnostic markers for Bartonella infections?

Several characteristics make ATP synthase components potential diagnostic targets:

Advantages:

• Essential, constitutively expressed proteins

• Species-specific sequence variations

• Potentially immunogenic

Potential diagnostic applications:

• Serological detection: Development of ELISAs using recombinant atpF1 or other subunits to detect Bartonella-specific antibodies in patient samples

• Molecular detection: Design of species-specific PCR primers targeting variable regions of ATP synthase genes

• Protein-based detection: Mass spectrometry detection of signature peptides from ATP synthase components

Research needs:

• Comprehensive immunogenicity studies

• Specificity testing against related alphaproteobacteria

• Validation with clinical samples from confirmed cases

The sequence differences observed between B. quintana and B. henselae atpF1 (approximately 7% divergence) suggest sufficient specificity for species discrimination in diagnostic applications .