Recombinant Bartonella henselae ATP synthase subunit b 1 (atpF1)

What is the metabolic role of ATP synthase in Bartonella henselae?

ATP synthase in B. henselae plays a critical role in energy generation through oxidative phosphorylation. Unlike many bacterial pathogens, B. henselae does not derive carbon and energy from glucose catabolism, which aligns with genome data suggesting an incomplete glycolytic pathway . Instead, B. henselae depletes amino acids from culture medium and accumulates ammonia, indicating amino acid catabolism . Analysis of the culture medium throughout the growth cycle reveals that oxygen is consumed and carbon dioxide is generated, suggesting that amino acids are catabolized in a tricarboxylic acid (TCA) cycle-dependent mechanism . Enzymatic assays of whole-cell lysates have confirmed that B. henselae possesses a complete TCA cycle . This unique metabolic profile makes ATP synthase particularly important for energy generation in this organism.

How does B. henselae ATP synthase compare with similar proteins in related species?

While specific structural information on B. henselae ATP synthase subunit b 1 is limited, we can draw parallels from B. quintana, a closely related species. The ATP synthase subunit b 1 (atpF1) in B. quintana consists of 188 amino acids and functions as part of the F₀ sector of ATP synthase . Both B. henselae and B. quintana ATP synthase components have been identified in proteomic analyses, with the alpha (atpA) and beta (atpD) chains being well-characterized . Interestingly, when studying oxidative phosphorylation in intracellular versus extracellular Bartonella, researchers observed downregulation of oxidative phosphorylation genes in intracellular bacteria, suggesting metabolic adaptation during infection .

What growth conditions affect ATP synthase expression and function in B. henselae?

B. henselae growth and metabolism (which directly impacts ATP synthase function) is unexpectedly sensitive to pH. Optimal growth occurs over a very narrow pH range (pH 6.8 to 7.2) . The doubling time in BBH-H medium at pH 7.2 is approximately 3 hours, representing a threefold reduction compared to previously reported growth rates . Growth rates decrease significantly at pH 6.6 and above pH 7.4, with no growth observed at pH 7.6 or higher . This pH sensitivity likely affects ATP synthase function, as this enzyme complex operates using a proton gradient across the membrane. ATP synthase activity may therefore be optimized for this specific pH range.

What expression systems are most effective for producing recombinant B. henselae atpF1?

Based on related recombinant protein studies with Bartonella proteins, E. coli BL21(DE3) expression systems with pET-based vectors have proven effective . When expressing B. henselae Pap31 protein, researchers confirmed successful expression by Sanger sequencing of plasmids isolated from the recombinant E. coli BL21(DE3) clones, verifying correct insertion and reading frame . Similar approaches would be appropriate for atpF1 expression.

For optimal expression, consider these parameters:

• Use strong inducible promoters (T7) with IPTG induction

• Expression temperature of 30°C may help with proper protein folding

• Include solubility tags if expression yields insoluble protein

• Codon optimization may improve expression efficiency

What purification strategies yield functional recombinant B. henselae atpF1?

From studies with other Bartonella proteins, purified recombinant proteins should yield a single band on Coomassie-stained SDS-PAGE and Western blot analysis . For storage, a Tris-based buffer with 50% glycerol at -20°C is recommended, with aliquoting to avoid repeated freeze-thaw cycles .

How can researchers verify the correct folding and function of recombinant atpF1?

To confirm proper folding and function of recombinant B. henselae atpF1:

• Structural integrity assessment:

  • Circular dichroism spectroscopy to evaluate secondary structure

  • Thermal shift assays to determine protein stability

  • Limited proteolysis to assess compact folding

• Functional analyses:

  • Protein-protein interaction studies with other ATP synthase subunits

  • Reconstitution experiments with other ATP synthase components

  • ATP hydrolysis assays with reconstituted complexes

• Binding studies:

  • Similar to studies with ATP binding to BepC's FIC domain, thermal stability assays can determine if nucleotide binding affects atpF1 stability

What techniques are most appropriate for studying atpF1 interactions with other ATP synthase components?

• Blue Native Polyacrylamide Gel Electrophoresis (BN-PAGE):

  • BN-PAGE has been successfully used to resolve ATP synthase complexes

  • Can be combined with in-gel ATPase activity assays to assess functionality

  • 2D BN/BN-PAGE can further separate complex components

• Co-immunoprecipitation:

  • Using antibodies against atpF1 or other subunits to pull down interacting partners

  • Mass spectrometry identification of co-precipitated proteins

• Cross-linking Mass Spectrometry:

  • Chemical cross-linking followed by MS analysis to identify spatial relationships

  • Helps determine the topology of atpF1 within the ATP synthase complex

• Single Particle Electron Microscopy:

  • Similar to analyses performed on ATP synthase from other organisms

  • Can reveal unique structural features of the Bartonella ATP synthase complex

How does ATP synthase activity in B. henselae compare to that in other bacteria?

B. henselae ATP synthase shows several distinctive characteristics compared to other bacterial ATP synthases:

• Inhibitor sensitivity profile:

  • Unusual resistance to classical F₀F₁ ATP synthase inhibitors like oligomycin and sodium azide

  • In contrast, yeast mitochondrial ATPase activity is inhibited 50% by 1 µM oligomycin and 91% by 1 mM sodium azide

• Activation characteristics:

  • Exhibits time- and ATP-dependent activation, as seen in other F₀F₁ ATP synthases/hydrolases

  • Somewhat lower specific ATPase activity compared to yeast

• Metabolic context:

  • Functions in a unique metabolic background where amino acids, not glucose, are the primary carbon source

  • Operates within a narrow pH optimum, suggesting specialized adaptation

How might recombinant B. henselae atpF1 be used in diagnostic applications?

Recombinant B. henselae atpF1 could potentially serve as an antigen for serological diagnostics, similar to other Bartonella proteins:

What is the potential of B. henselae ATP synthase as a therapeutic target?

ATP synthase in B. henselae presents several characteristics that make it a potentially attractive therapeutic target:

• Essential metabolic function:

  • Critical for energy generation in a pathogen with limited metabolic flexibility

  • Downregulation of oxidative phosphorylation genes in intracellular bacteria suggests metabolic adaptation

• Unique inhibitor profile:

  • Resistance to conventional ATP synthase inhibitors suggests structural uniqueness

  • Potential for developing Bartonella-specific ATP synthase inhibitors

• Target validation approach:

  • Gene knockout or knockdown studies to confirm essentiality

  • Structure-based drug design targeting unique features of B. henselae ATP synthase

  • Screening for inhibitors that selectively target B. henselae ATP synthase over human homologs

How does ATP synthase expression change during B. henselae infection?

Studies on Bartonella gene expression during infection provide insights into ATP synthase regulation:

• Downregulation during intracellular phase:

  • Transcriptomic profiles indicate downregulation of oxidative phosphorylation genes in intracellular bacteria

  • This suggests metabolic adaptation to exploit host resources efficiently

• Stringent response connection:

  • The downregulation could be linked to the stringent response, as components like DksA and SpoT are downregulated in intracellular bacteria

  • This may represent an energy conservation strategy during infection

• Implications for bacterial persistence:

  • Metabolic adaptation may contribute to long-term persistence within host cells

  • Understanding these changes could reveal vulnerabilities in the bacterial life cycle

What genetic approaches can be used to study ATP synthase function in B. henselae?

• Gene knockout/knockdown strategies:

  • CRISPR-Cas9 systems adapted for Bartonella

  • Conditional expression systems if atpF1 is essential

  • Antisense RNA approaches for partial inhibition

• Reporter gene fusion systems:

  • Promoter-reporter fusions to study expression regulation

  • Protein-reporter fusions to study localization and complex formation

• Site-directed mutagenesis:

  • Target conserved residues to assess functional importance

  • Create chimeric proteins with subunits from other species to identify species-specific functions

• Complementation studies:

  • Express B. henselae atpF1 in other bacterial species with ATP synthase mutations

  • Assess functional conservation and species-specific adaptations

How can researchers effectively study ATP synthase in the context of B. henselae pathogenesis?

• Cell infection models:

  • Infection of relevant host cells (endothelial cells, erythrocytes)

  • Measurement of ATP synthase expression and activity during infection

  • Assessment of the impact of ATP synthase inhibition on infection

• Integration with virulence factor studies:

  • Investigate potential relationships between ATP synthase and the VirB/VirD4 Type IV Secretion System

  • Examine energetic requirements for secretion of Bartonella effector proteins

• In vivo approaches:

  • Animal models of B. henselae infection to study ATP synthase expression in different tissues

  • Impact of metabolic modulators on infection outcome

• Transcriptomic/proteomic analysis:

  • Compare expression profiles of ATP synthase components under different conditions

  • Correlate with expression of virulence factors and stress response genes

What are the most reliable methods for quantifying B. henselae in experimental systems?

For accurate quantification of B. henselae in experimental systems:

• Quantitative PCR approaches:

  • Target the highly conserved 16S rRNA gene

  • Can detect single copies of the bacterial genome

  • Commercial kits are available with validated primers and probes

• Growth measurement in specialized media:

  • BBH-H medium supports growth to densities of 5×10⁸ to 1×10⁹ CFU/ml

  • Optimal pH range (6.8-7.2) is critical for reliable growth

• Microscopic enumeration:

  • Fluorescent labeling for direct visualization

  • Immunofluorescence with antibodies against B. henselae antigens

• Flow cytometry:

  • Fluorescent labeling of bacteria for high-throughput counting

  • Discrimination between live and dead bacteria using viability dyes

How does ATP synthase from B. henselae compare with homologs in other intracellular pathogens?

• Structural and functional comparison:

  • B. henselae and B. quintana ATP synthase components show high similarity

  • Both species rely on amino acid catabolism rather than glycolysis

• Inhibitor sensitivity profiles:

  • B. henselae ATP synthase shows unusual resistance to oligomycin and sodium azide

  • This differs from many other bacterial ATP synthases, suggesting unique structural features

• Expression regulation during infection:

  • Downregulation of oxidative phosphorylation genes in intracellular bacteria is observed in Bartonella

  • This may be a common adaptation strategy among intracellular pathogens

What evolutionary insights can be gained from studying B. henselae ATP synthase?

The study of B. henselae ATP synthase provides several evolutionary insights:

• Metabolic adaptation:

  • The reliance on amino acid catabolism rather than glucose metabolism represents a specialized adaptation to the host environment

  • The loss of hexokinase and phosphofructokinase genes indicates evolutionary streamlining of metabolism

• Host-pathogen co-evolution:

  • The unusual inhibitor resistance profile suggests evolutionary divergence from other bacterial ATP synthases

  • This may represent adaptation to specific host environments or defense against host-derived inhibitory molecules

• Conservation within Bartonella genus:

  • Comparison of ATP synthase components across Bartonella species could reveal conserved features essential for the genus lifestyle

  • Species-specific variations might indicate adaptation to different mammalian hosts

ATP synthase appears to be part of a broader evolutionary strategy in Bartonella that focuses on conserving energy through downregulation of protein synthesis during intracellular phases while maintaining essential metabolic functions .