Recombinant Bordetella petrii ATP synthase subunit a (atpB)

What is the function of ATP synthase subunit a (atpB) in Bordetella petrii?

ATP synthase subunit a (atpB) is a critical membrane-embedded component of the F₀ sector of ATP synthase in Bordetella petrii. This protein forms part of the proton channel that couples proton translocation across the membrane to ATP synthesis. In Bordetella species, the ATP synthase complex plays an essential role in energy metabolism by generating ATP through oxidative phosphorylation. Transcriptional analysis has confirmed the expression of atpB in various conditions, indicating its fundamental importance to cellular bioenergetics . The protein's role extends beyond basic metabolism, as ATPase activity has been shown to be significantly inhibited by DCCD (dicyclohexylcarbodiimide) and ionophores in acid-adapted cells, suggesting regulatory adaptations under stress conditions .

What techniques are most effective for purifying recombinant B. petrii atpB protein?

Purification of recombinant B. petrii atpB presents specific challenges due to its hydrophobic nature as a membrane protein. The most effective purification approach involves:

• Expression system selection: E. coli BL21(DE3) with pET expression vectors containing a C-terminal His-tag has shown good results for membrane proteins from Bordetella.

• Solubilization optimization: Using mild detergents such as n-dodecyl β-D-maltoside (DDM) or lauryl maltose neopentyl glycol (LMNG) at 1-2% concentration effectively solubilizes atpB while preserving its native structure.

• Purification protocol:

  • Initial purification using Ni-NTA affinity chromatography

  • Secondary purification via size exclusion chromatography

  • Final polishing with ion exchange chromatography if needed

• Quality assessment: Verification of protein purity by SDS-PAGE and Western blotting using antibodies specific to the His-tag or to the atpB protein.

This multi-step approach typically yields protein with >90% purity suitable for structural and functional studies. When designing expression constructs, researchers should consider removing potential unstable regions while preserving functional domains.

How can researchers effectively examine the regulation of atpB expression in B. petrii under different environmental conditions?

Investigating atpB expression regulation in B. petrii requires a systematic approach combining transcriptional analysis with physiological studies:

• Transcriptional analysis methodology:

  • Real-time quantitative PCR (RT-qPCR) targeting the atpB transcript under various conditions (pH, temperature, nutrient limitation)

  • RNA-seq for genome-wide transcriptional response analysis

  • 5' RACE to identify transcription start sites and potential regulatory elements

• Reporter system construction:

  • Creation of atpB promoter-reporter fusions (e.g., lacZ, gfp) to monitor promoter activity

  • Site-directed mutagenesis of potential regulatory regions to identify critical regulatory elements

• Environmental condition testing protocol:

  • Acid stress response: Culture adaptation at pH values ranging from 5.0-8.0

  • Metal ion influence: Supplementation with varying concentrations of Mn²⁺, Ca²⁺, and other divalent cations

  • Nutrient limitation: Carbon, nitrogen, and phosphate restriction

• Data analysis approach:

  • Normalization to housekeeping genes (e.g., 16S rRNA, rpoD)

  • Statistical analysis using ANOVA with post-hoc tests

  • Integration with proteomic data for correlation between transcription and translation

Based on patterns observed in related Bordetella species, researchers should pay particular attention to the influence of manganese on gene expression, as manganese has been shown to regulate expression of certain genes in B. pertussis through riboswitch mechanisms . Additionally, the response to acid stress is likely significant, as atpB expression has been linked to acid adaptation mechanisms in related bacteria .

What is the role of B. petrii atpB in bacterial adaptation to manganese exposure?

While direct evidence for B. petrii atpB's role in manganese adaptation is limited, insights from related Bordetella species suggest important connections. In B. pertussis, manganese exposure activates specific genes through riboswitch mechanisms . The ATP synthase complex likely participates in the cellular response to manganese through several mechanisms:

• Energy provision for detoxification: ATP synthase activity provides the energy required for manganese efflux systems, helping maintain appropriate intracellular manganese concentrations.

• Membrane potential maintenance: atpB's role in proton translocation contributes to membrane potential homeostasis, which can be disrupted by excessive manganese.

• Regulatory crosstalk: Transcriptional analysis reveals potential regulatory connections between manganese response elements and atpB expression, suggesting coordinated regulation under metal stress.

Research methodology for investigating this relationship should include:

• Constructing atpB deletion or point mutants and assessing their growth and survival under varying manganese concentrations

• Measuring ATP synthesis rates and proton motive force in wild-type versus mutant strains

• Membrane proteomics to detect changes in ATP synthase complex assembly and stability

When examining atpB expression under manganese exposure, researchers should use a range of Mn²⁺ concentrations (100-800 μM) and assess both immediate responses (60 min exposure) and adaptive responses (24-48 hour exposure) .

How does atpB function interact with nicotinic acid metabolism in Bordetella species?

The interaction between ATP synthase and nicotinic acid metabolism represents an important research area, particularly given Bordetella's auxotrophy for NAD precursors. Bordetella species require nicotinamide, quinolinic acid, or nicotinic acid for NAD biosynthesis, which is essential for energy metabolism . The relationship between atpB and nicotinic acid metabolism involves several interconnected pathways:

• Energetic coupling: ATP generated by ATP synthase provides energy for nicotinic acid uptake and metabolism.

• Regulatory interactions: The nic locus in B. bronchiseptica, which encodes a nicotinic acid degradation pathway, shows regulatory connections to energy metabolism genes.

• Impact on virulence regulation: Dysregulation of the nicotinic acid degradation pathway affects BvgAS-mediated virulence gene regulation, demonstrating that fluctuation of intracellular nicotinic acid pools impacts virulence transitions .

To investigate these interactions, researchers should:

• Construct double mutants affecting both atpB and nicotinic acid metabolism genes

• Measure intracellular NAD+/NADH ratios in wild-type versus atpB mutants under varying nicotinic acid availability

• Assess ATP synthesis capacity in strains with altered nicotinic acid metabolism

A recommended experimental approach involves cultivating B. petrii in media with controlled nicotinic acid concentrations (1-100 μM) and measuring both ATP synthase activity and expression of nicotinic acid metabolism genes to establish correlation patterns.

What structural and functional modifications could enhance the stability of recombinant B. petrii atpB for experimental applications?

Enhancing the stability of recombinant B. petrii atpB requires strategic modifications while preserving its functional integrity:

The most promising approach combines minimal N-terminal truncation (first 10-15 residues) with the addition of a C-terminal thioredoxin fusion and selected surface mutations in loop regions. Researchers should verify that modifications maintain proton translocation function through complementation studies in ATP synthase-deficient strains.

How does the mechanism of B. petrii ATP synthase compare to other bacterial pathogens in terms of adaptation to host environments?

Bordetella petrii ATP synthase, including its atpB subunit, demonstrates distinct adaptations compared to other bacterial pathogens:

• Acid tolerance response: Unlike many enteric pathogens that encounter extreme acid stress, Bordetella species face moderate pH fluctuations in the respiratory tract. Accordingly, B. petrii ATP synthase appears adapted for optimal function at slightly acidic to neutral pH, with ATPase activity significantly inhibited by DCCD and ionophores in acid-adapted cells .

• Metal ion interactions: The complex interplay between metal ions (particularly Mn²⁺ and Ca²⁺) and ATP synthase function reflects adaptation to the metal-restricted host environment. In B. pertussis, manganese exposure induces specific gene expression through riboswitch mechanisms , potentially including genes related to energy metabolism.

• Integration with virulence regulation: The ATP synthase complex likely functions in concert with virulence regulation systems. Research on related Bordetella species indicates that BteA-induced cytotoxicity disrupts calcium homeostasis, leading to mitochondrial dysfunction , suggesting connections between energy metabolism and virulence mechanisms.

To investigate these comparative adaptations, researchers should employ:

• Cross-species complementation studies with atpB from different pathogens

• In vitro reconstitution of ATP synthase complex containing B. petrii atpB under varying conditions

• Computational modeling to identify species-specific structural adaptations

These approaches will illuminate how B. petrii ATP synthase has evolved specific adaptations to its environmental niche, which differs from both highly specialized human pathogens like B. pertussis and environmental bacteria.

What are the optimal conditions for measuring B. petrii ATP synthase activity in membrane preparations?

Accurate measurement of B. petrii ATP synthase activity requires careful preparation and controlled assay conditions:

• Membrane preparation protocol:

  • Harvest cells in late exponential phase

  • Disrupt cells by sonication (10×15s pulses, 40% amplitude) in buffer containing 50 mM Tris-HCl pH 7.5, 10% glycerol, 1 mM DTT, and protease inhibitor cocktail

  • Remove unbroken cells by centrifugation (10,000×g, 10 min)

  • Collect membranes by ultracentrifugation (150,000×g, 1 hour)

  • Resuspend membrane pellet in 50 mM Tris-HCl pH 7.5, 10% glycerol, 5 mM MgCl₂

• ATP synthesis measurement:

  • Establish proton gradient by acidification to pH 5.5 followed by rapid dilution into pH 8.0 buffer

  • Include 5 mM succinate as respiratory substrate

  • Add 200 μM ADP and 5 mM Pi

  • Quantify ATP production using luciferase-based assay

• ATP hydrolysis measurement:

  • Assay buffer: 50 mM Tris-HCl pH 8.0, 5 mM MgCl₂, 100 mM KCl

  • Add 5 mM ATP to initiate reaction

  • Monitor inorganic phosphate release using malachite green assay

  • Include control reactions with 100 μM DCCD to confirm ATP synthase specificity

• Optimal reaction conditions:

  • Temperature: 30°C

  • pH range: 6.8-8.0

  • Mg²⁺ concentration: 5-10 mM

  • KCl concentration: 100-150 mM

Activity measurements should include internal standards and appropriate controls to account for background ATPase activity from other membrane proteins. When testing inhibitors or environmental conditions, pre-incubate membrane preparations for 5-10 minutes before initiating activity measurements.

How can researchers effectively analyze the impact of mutations in the atpB gene on B. petrii physiology?

Comprehensive analysis of atpB mutations requires a multi-faceted approach:

• Mutagenesis strategy:

  • Site-directed mutagenesis targeting conserved residues in proton channel

  • Random mutagenesis with selection for specific phenotypes

  • Construction of chimeric proteins with atpB regions from related species

• Phenotypic characterization protocol:

  • Growth curve analysis in minimal and rich media

  • Determination of doubling times and lag phases

  • Assessment of growth under stress conditions (pH, temperature, oxidative stress)

• Bioenergetic measurements:

  • Membrane potential using fluorescent probes (DiSC3(5))

  • Intracellular ATP levels using luciferase-based assays

  • Oxygen consumption rate measurement

  • pH homeostasis using pH-sensitive fluorescent proteins

• Structural analysis approaches:

  • Protein modeling to predict mutation effects

  • Cross-linking studies to assess protein-protein interactions

  • Membrane insertion efficiency analysis

• Complementation analysis:

  • Expression of wild-type atpB in mutant strains

  • Heterologous expression of mutant atpB in model organisms

What is the relationship between B. petrii atpB function and the bacterial response to oxidative stress?

The relationship between ATP synthase function and oxidative stress response in B. petrii represents an important research area with implications for pathogenesis and environmental adaptation:

• Mechanistic connections:

  • ATP synthase maintains proton motive force needed for antioxidant defense systems

  • ATP production provides energy for repair of oxidative damage

  • Proton translocation affects cytoplasmic pH, which influences ROS formation

• Experimental approach for investigation:

  • Expose wild-type and atpB mutant strains to oxidative stressors (H₂O₂, paraquat)

  • Measure survival rates and morphological changes

  • Assess expression of oxidative stress response genes (catalase, superoxide dismutase)

  • Quantify intracellular ROS levels using fluorescent probes

• Analytical considerations:

  • Control for growth phase effects (exponential vs. stationary)

  • Account for medium composition impacts on ROS generation

  • Use multiple oxidative stressors to distinguish specific response pathways

• Integration with other stress responses:

  • Examine the interplay between acid stress and oxidative stress responses

  • Investigate connections to metal ion homeostasis, particularly manganese, which functions in antioxidant defense

The dual role of ATP synthase in both energy production and maintenance of proton gradients positions it as a central player in stress response networks. Researchers should employ transcriptomic and proteomic approaches to map the regulatory connections between atpB expression/function and oxidative stress response pathways.

How does B. petrii atpB contribute to the proton motive force and pH homeostasis during environmental adaptation?

The atpB subunit plays a central role in proton translocation and pH homeostasis in B. petrii, contributing to adaptation across environmental conditions:

• Proton motive force generation and utilization:

  • atpB forms part of the proton channel through which H⁺ ions flow down their electrochemical gradient

  • This flow drives the conformational changes required for ATP synthesis

  • Under certain conditions, ATP synthase can reverse, hydrolyzing ATP to pump protons and maintain membrane potential

• pH homeostasis mechanisms:

  • Internal pH regulation depends partially on ATP synthase activity

  • When cytoplasmic pH decreases, ATP synthase can shift to favor proton extrusion

  • Transcriptional analysis reveals that atpB expression is modified in acid-adapted cells

• Research methodology for investigation:

  • Measure internal pH using pH-sensitive fluorescent proteins in wild-type vs. atpB mutants

  • Determine proton motive force components (ΔpH and ΔΨ) using appropriate fluorescent probes

  • Analyze expression kinetics of atpB and other ATP synthase genes during acid adaptation

  • Assess the impact of protonophores on growth and survival of wild-type vs. atpB mutants

• Environmental adaptation considerations:

  • Different growth environments will affect the optimal operation of ATP synthase

  • Researchers should examine atpB function across a pH range (pH 5.5-8.0) relevant to B. petrii's environmental niches

  • The relationship between nutrient availability and ATP synthase function should be established through growth in defined media with varying carbon sources

The dual role of ATP synthase in both energy production and pH homeostasis makes it a critical component of B. petrii's adaptability to diverse environments, from soil to opportunistic host associations.

What potential interactions exist between B. petrii atpB and the virulence mechanisms in pathogenic Bordetella species?

Although B. petrii is generally considered an environmental species, research on pathogenic Bordetella provides insights into potential interactions between ATP synthase and virulence mechanisms that may be relevant for B. petrii in opportunistic infections:

Understanding these interactions provides insight into the evolutionary relationships between environmental Bordetella species and their pathogenic relatives, potentially revealing how metabolic systems like ATP synthase have been co-opted or modified during adaptation to pathogenicity.

How can structural modeling aid in understanding the functional domains of B. petrii atpB?

Structural modeling provides valuable insights into atpB function without requiring crystal structures, which are challenging to obtain for membrane proteins:

• Homology modeling approach:

  • Identify suitable templates from related ATP synthase structures (E. coli, Mycobacterium, mitochondrial)

  • Perform sequence alignment with careful attention to transmembrane regions

  • Generate multiple models using different algorithms (SWISS-MODEL, I-TASSER, AlphaFold2)

  • Validate models through Ramachandran plots, QMEAN scores, and ProSA

• Critical structural features to analyze:

  • Transmembrane helices forming the proton channel

  • Arginine residue involved in proton translocation

  • Interface regions with other ATP synthase subunits

  • Potential metal-binding sites

• Functional domain prediction:

  • Map conserved residues onto structural model

  • Identify potential sites for mutagenesis

  • Predict effects of natural variations between Bordetella species

• Molecular dynamics simulation protocol:

  • Embed model in lipid bilayer matching bacterial membrane composition

  • Perform energy minimization and equilibration

  • Run production simulations (100-500 ns) to analyze stability and dynamics

  • Investigate proton translocation pathway using specialized techniques

• Experimental validation strategies:

  • Site-directed mutagenesis of predicted functional residues

  • Cross-linking studies guided by structural predictions

  • Suppressor mutation analysis to validate interaction surfaces

The resulting structural insights can guide experimental design and help interpret phenotypic effects of mutations, advancing understanding of atpB function in B. petrii and related species.

What potential exists for targeting B. petrii atpB in therapeutic or biotechnological applications?

The unique characteristics of B. petrii ATP synthase present several opportunities for research applications:

• Antimicrobial development strategies:

  • While B. petrii is not typically pathogenic, insights from its ATP synthase could inform development of targeted therapies against related respiratory pathogens

  • ATP synthase inhibitors with specificity for bacterial over mitochondrial enzymes represent potential narrow-spectrum antibiotics

  • Structure-based drug design targeting unique features of Bordetella ATP synthase could yield novel compounds

• Biotechnological applications:

  • The unique regulatory features of B. petrii ATP synthase, particularly its response to environmental signals, could be exploited for engineered biosensors

  • ATP synthase components could be incorporated into synthetic biology circuits for energy regeneration

  • The protein could serve as a model for engineering proton pumps with altered specificity or regulation

• Research tool development:

  • Engineered variants of atpB could serve as reporters for environmental conditions

  • The protein's metal-responsive properties could be harnessed for metal detection systems

  • Structural insights could inform the design of membrane protein expression and purification strategies

• Recommended research approaches:

  • High-throughput screening of compound libraries against purified ATP synthase complex

  • Directed evolution to generate atpB variants with enhanced stability or altered function

  • Structural biology combined with computational design for rational engineering

Future research should focus on detailed characterization of the unique properties of B. petrii ATP synthase compared to other bacterial and mitochondrial enzymes to identify exploitable differences.

How can systems biology approaches enhance our understanding of B. petrii atpB in cellular networks?

Systems biology provides a framework for understanding atpB's role within the broader context of cellular metabolism and regulation:

• Multi-omics integration methodology:

  • Combine transcriptomics, proteomics, and metabolomics data from wild-type and atpB mutant strains

  • Generate condition-specific datasets across environmental perturbations

  • Apply computational integration techniques including correlation networks and flux balance analysis

• Regulatory network reconstruction:

  • Identify transcription factors regulating atpB expression

  • Map post-translational modifications affecting ATP synthase function

  • Characterize feedback loops connecting energy status to gene expression

• Metabolic modeling approach:

  • Construct genome-scale metabolic models incorporating ATP synthase function

  • Perform flux balance analysis to predict the impact of ATP synthase perturbations

  • Validate predictions through experimental measurement of metabolic fluxes

• Experimental design considerations:

  • Design experiments with sufficient biological replicates for statistical power

  • Include time-series measurements to capture dynamic responses

  • Incorporate multiple environmental conditions to build comprehensive models

• Data analysis pipeline:

  • Apply machine learning techniques to identify patterns in multi-omics data

  • Use network analysis to identify hub genes and key regulatory connections

  • Develop predictive models for cellular responses to ATP synthase perturbation

Through these approaches, researchers can develop a comprehensive understanding of how atpB function integrates with cellular metabolism, stress responses, and potentially virulence-associated pathways, providing a foundation for both basic research and applied studies.