Recombinant Legionella pneumophila ATP synthase subunit delta (atpH)

What is the role of ATP synthase subunit delta (atpH) in Legionella pneumophila metabolism?

ATP synthase subunit delta (atpH) in L. pneumophila is a crucial component of the F1 sector of ATP synthase, forming part of the stalk that connects the F1 catalytic domain to the F0 membrane-embedded domain. This 180-amino acid protein (designated as lpg2985 in the L. pneumophila genome) participates in the coupling mechanism that translates proton movement through the F0 sector into conformational changes in F1, ultimately leading to ATP synthesis.

Transcriptomic analysis reveals that atpH expression is downregulated in water environments (log2 ratio of -1.89 at 2 hours and -2.15 at 6 hours), suggesting reduced energy production during environmental persistence . This reduction in ATP synthase expression appears to be part of a broader metabolic shift when L. pneumophila transitions between different growth phases or environments.

The coordination of atpH with other ATP synthase subunits (including atpA, atpB, atpC, atpD, atpE, atpG, and atpI) is essential for proper energy metabolism in L. pneumophila, which in turn supports various cellular processes including virulence mechanisms required during infection.

How is atpH gene expression regulated in L. pneumophila during different growth phases?

Expression of atpH in L. pneumophila demonstrates significant growth phase-dependent regulation. Transcriptomic data indicates a coordinated downregulation of multiple ATP synthase components (including atpH) when bacteria transition from nutrient-rich to water environments:

This pattern suggests that ATP synthase expression is tightly controlled in response to environmental conditions . The downregulation correlates with reduced metabolic activity during stationary phase or environmental persistence.

The regulatory networks governing atpH expression likely include the LetA/LetS two-component system, which plays a key role in controlling the transition between replicative and transmissive forms of L. pneumophila . This system influences the expression of numerous genes associated with different growth phases and virulence, potentially including metabolic genes like atpH.

How does atpH expression change when L. pneumophila transitions from water environments to intracellular growth?

Transcriptomic data shows significant downregulation of atpH (lpg2985) and other ATP synthase components when L. pneumophila is in water environments, with atpH showing a log2 ratio of -1.89 at 2 hours and -2.15 at 6 hours . This pattern suggests reduced energy metabolism during environmental persistence.

When transitioning to intracellular growth within host cells (amoebae or human macrophages), L. pneumophila must adapt its metabolism to exploit available nutrients and establish a replicative niche. Although specific data on atpH upregulation during infection isn't provided in the search results, the general metabolic pattern suggests ATP synthase components would be upregulated during active intracellular replication.

This transition involves significant metabolic reprogramming, including expression changes in genes regulated by the LetA/LetS two-component system . The upregulation of energy metabolism genes would support the energy requirements for various virulence mechanisms, including the Dot/Icm type IV secretion system essential for establishing the Legionella-containing vacuole .

What experimental approaches can be used to study the interaction between atpH and other components of the ATP synthase complex in L. pneumophila?

Multiple complementary approaches can be employed to study interactions between atpH and other ATP synthase components:

• Co-immunoprecipitation (Co-IP): Using antibodies against tagged recombinant atpH to pull down associated proteins, followed by mass spectrometry identification. This approach can preserve native protein complexes .

• Bacterial two-hybrid systems: These can test specific binary interactions between atpH and other ATP synthase subunits in a cellular context.

• Cross-linking studies: Chemical cross-linkers can capture transient interactions within the ATP synthase complex, followed by proteomic analysis to identify linked components.

• Reconstitution experiments: Purified recombinant ATP synthase components can be combined in vitro to assess complex formation and function. This approach has been used successfully with other L. pneumophila proteins .

• Cryo-electron microscopy: For structural visualization of the complete ATP synthase complex, revealing the position and interactions of atpH within the assembled machinery.

• FRET (Förster Resonance Energy Transfer): By tagging atpH and interacting partners with appropriate fluorophores, interaction dynamics can be studied in living bacteria.

• Surface plasmon resonance (SPR): This can quantitatively measure binding affinities between atpH and other components of the complex.

For all approaches, using properly folded recombinant atpH (>85% purity) with appropriate storage conditions is crucial for maintaining native interactions .

How can recombinant atpH be used to investigate L. pneumophila energy metabolism during intracellular infection?

Recombinant L. pneumophila atpH can be employed in several ways to study energy metabolism during infection:

• Antibody development: Using recombinant atpH to generate specific antibodies for immunofluorescence microscopy to track ATP synthase localization and abundance during different infection stages.

• In vitro reconstitution studies: Combining recombinant atpH with other ATP synthase components to measure ATP synthesis under conditions mimicking the intracellular environment.

• Structure-function analysis: Creating site-directed mutants of recombinant atpH to identify critical residues for ATP synthase activity and testing their effects on bacterial fitness during infection.

• Protein-protein interaction studies: Using recombinant atpH as bait to identify infection-specific binding partners that might regulate ATP synthase activity.

• Comparative biochemistry: Analyzing the properties of L. pneumophila atpH versus host mitochondrial ATP synthase delta subunit to understand pathogen-specific adaptations.

This research is particularly relevant considering that L. pneumophila actively modulates host energy metabolism during infection, as evidenced by the targeting of mitochondrial ADP/ATP translocases (ANTs) by effector proteins Lpg0080 and Lpg0081 , and the secretion of a mitochondrial carrier protein involved in ATP transport .

What are the challenges in purifying functionally active recombinant atpH and how can they be overcome?

Purification of functionally active recombinant L. pneumophila atpH presents several challenges:

• Protein solubility: As part of a multi-subunit complex, atpH may expose hydrophobic surfaces when expressed alone, reducing solubility.

  • Solution: Use solubility-enhancing tags (MBP, SUMO) or optimize buffer conditions with stabilizing agents.

• Proper folding: Ensuring correct tertiary structure is essential for functional studies.

  • Solution: Optimize expression conditions (temperature, induction time) and consider chaperone co-expression systems.

• Aggregation during concentration: atpH may aggregate when concentrated for structural studies.

  • Solution: Include stabilizing agents (glycerol, specific detergents) and use gentle concentration methods.

• Expression system selection: Different systems offer various advantages and limitations.

  • Solution: Mammalian cell expression systems have been successful for L. pneumophila atpH , while yeast systems have worked for homologous proteins from other bacteria .

• Storage stability: Maintaining functional integrity during storage.

  • Solution: Store in deionized sterile water with 5-50% glycerol at -20°C/-80°C as recommended for this specific protein .

• Functional validation: Confirming that purified atpH retains its native activity.

  • Solution: Develop binding assays with other ATP synthase components or activity assays in reconstituted systems.

Aim for >85% purity (as indicated in product specifications ) and validate using multiple techniques (SDS-PAGE, mass spectrometry, circular dichroism) to confirm proper size, identity, and folding.

How does atpH contribute to L. pneumophila virulence and pathogenesis?

While the direct contribution of atpH to L. pneumophila virulence isn't explicitly detailed in the search results, its role can be inferred from energy requirements during infection:

• Energy for virulence mechanisms: The Dot/Icm type IV secretion system, essential for L. pneumophila pathogenesis , requires significant energy for assembly and function. ATP synthase, including atpH, would be critical for generating this energy.

• Metabolic adaptation during infection: L. pneumophila must adjust its metabolism when transitioning from environmental water to the intracellular environment of host cells. This adaptation includes regulation of ATP synthase components, with atpH being downregulated in water environments but likely upregulated during intracellular replication.

• Survival in diverse environments: L. pneumophila must maintain energy homeostasis across various pH conditions. The bacterium shows reduced viability at pH 8 compared to pH 4-7 , which may relate to the function of pH-dependent enzymes including ATP synthase.

• Connection to virulence regulation: The LetA/LetS two-component system regulates both virulence factors and the switch between replicative and transmissive phases . This regulatory network likely influences metabolic gene expression, including ATP synthase components.

The importance of energy metabolism in L. pneumophila pathogenesis is further highlighted by the bacterium's targeting of host energy systems through effector proteins that modify mitochondrial ADP/ATP translocases and inhibit host v-ATPase .

What are the best methodologies for studying atpH-associated protein-protein interactions in L. pneumophila?

Several complementary approaches can be used to study atpH protein interactions in L. pneumophila:

• Co-immunoprecipitation (Co-IP): This method can identify proteins that interact with atpH in their native state:

  • Express tagged atpH in L. pneumophila

  • Lyse cells under non-denaturing conditions with TBS buffer (150 mM NaCl, 50 mM Tris-HCl, pH 7.5) containing 1% Triton X-100

  • Capture atpH complexes using tag-specific antibody-coated beads

  • Wash thoroughly and identify binding partners by immunoblotting or mass spectrometry

• Pull-down assays with recombinant proteins:

  • Immobilize purified recombinant atpH (>85% purity ) on affinity resin

  • Incubate with L. pneumophila lysate

  • Elute and identify specifically bound proteins

  • This approach can be modified using macrodomain proteins like Af1521 to identify specifically modified interaction partners

• Cross-linking coupled with mass spectrometry (XL-MS):

  • Treat intact bacteria or purified complexes with chemical cross-linkers

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

  • This approach can capture transient interactions within the ATP synthase complex

• Bacterial two-hybrid systems:

  • Create fusion proteins with atpH and potential partners

  • Co-express in a bacterial host and measure reporter activation

  • Useful for confirming specific binary interactions

• Microscopy-based approaches:

  • Fluorescence colocalization

  • FRET (Förster Resonance Energy Transfer)

  • BiFC (Bimolecular Fluorescence Complementation)

  • These methods can visualize interactions in living bacteria

Validation through multiple independent methods is essential, as is the inclusion of appropriate controls to distinguish specific from non-specific interactions.

What expression systems are optimal for producing recombinant L. pneumophila atpH?

Several expression systems can be considered for producing recombinant L. pneumophila atpH:

• Mammalian cell expression systems: According to product information, recombinant L. pneumophila atpH has been successfully produced in mammalian cells . Advantages include:

  • Proper protein folding

  • Potential for native-like post-translational modifications

  • Reduced endotoxin contamination

• Yeast expression systems: Used successfully for homologous ATP synthase subunits from other bacteria . Benefits include:

  • Eukaryotic protein processing machinery

  • High yield potential

  • Cost-effective scale-up

  • Suitable for proteins potentially toxic to bacteria

• E. coli expression systems: While not specifically mentioned for L. pneumophila atpH, E. coli remains the most common bacterial expression system due to:

  • High protein yields

  • Rapid growth and simple cultivation

  • Well-established protocols and reagents

  • Various specialized strains for difficult proteins

For optimal results with L. pneumophila atpH:

• Purification tags: His-tag has been used successfully

• Storage conditions: Reconstitution in deionized sterile water at 0.1-1.0 mg/mL with 5-50% glycerol, stored at -20°C to -80°C

• Quality assessment: Aim for >85% purity as verified by SDS-PAGE

The selection of expression system should be guided by the intended application, with mammalian or yeast systems potentially offering advantages for structural or functional studies requiring properly folded protein.

How can researchers generate antibodies against L. pneumophila atpH for immunological studies?

Generating high-quality antibodies against L. pneumophila atpH requires strategic planning:

• Antigen preparation options:

  • Full-length recombinant protein: Using the complete 180-amino acid sequence of atpH provides all potential epitopes

  • Peptide antigens: Selecting 15-20 amino acid sequences from predicted surface-exposed regions

  • Properly folded protein: Essential for applications requiring recognition of native protein conformation

• Antibody production approaches:

  • Polyclonal antibodies:

    • Immunize rabbits or other animals with purified recombinant atpH

    • Purify IgG fraction from serum

    • Advantages: Multiple epitope recognition, robust signal

  • Monoclonal antibodies:

    • Generate hybridomas after immunization

    • Screen for specific antibody production

    • Advantages: Consistent specificity, renewable resource

• Validation strategies:

  • Western blot against recombinant atpH (>85% purity ) and L. pneumophila lysates

  • Immunoprecipitation followed by mass spectrometry

  • Immunofluorescence microscopy with appropriate controls

  • ELISA with recombinant atpH and related proteins to assess cross-reactivity

• Practical considerations:

  • Use removable affinity tags for immunization to avoid tag-directed antibodies

  • Consider cross-reactivity with host ATP synthase components if antibodies will be used in infection studies

  • For detecting native complexes, use mild lysis conditions (TBS with 1% Triton X-100)

Successful antibody generation will provide valuable tools for tracking atpH expression, localization, and interactions during different phases of L. pneumophila growth and infection.

What are the best approaches for assessing ATP synthase activity in relation to atpH function?

To evaluate ATP synthase activity with a focus on atpH function, several complementary methods can be employed:

• ATP synthesis/hydrolysis assays:

  • Reconstituted systems: Purified components including recombinant atpH can be reconstituted in liposomes to measure ATP synthesis upon establishment of a proton gradient

  • Bacterial membrane vesicles: Inverted membrane vesicles prepared from L. pneumophila with wild-type or mutant atpH

  • Colorimetric phosphate release assays: Measuring inorganic phosphate produced during ATP hydrolysis

• Proton translocation measurements:

  • pH-sensitive fluorescent dyes: To monitor proton movement across membranes

  • pH electrode measurements: To directly measure pH changes in real-time

• Structure-function studies:

  • Site-directed mutagenesis: Creating specific mutations in atpH to identify critical residues

  • Deletion analysis: Testing truncated versions to map functional domains

• Complex assembly assessment:

  • Blue Native PAGE: To visualize intact ATP synthase complexes

  • Immunoprecipitation: To detect interactions between atpH and other components

• Comparative analyses:

  • Growth conditions: ATP synthase activity differs significantly between growth phases, with components like atpH downregulated in water environments (log2 ratio of -1.89 at 2hr and -2.15 at 6hr)

  • pH sensitivity: L. pneumophila shows reduced viability at pH 8 compared to pH 4-7 , which may relate to ATP synthase function

These methods can help understand how atpH contributes to ATP synthase function during different phases of the L. pneumophila lifecycle, from environmental persistence to intracellular replication.

How can gene knockout or knockdown studies be designed to investigate atpH function in L. pneumophila?

Effective gene knockout or knockdown studies for atpH in L. pneumophila can be designed using several approaches:

• Complete gene knockout strategies:

  • Homologous recombination: Replace atpH with an antibiotic resistance marker

  • Unmarked deletion methods: Generate clean deletions without antibiotic markers, which "facilitate studies of Legionella pneumophila"

  • RecA-independent recombination: Can be harnessed for genetic engineering of L. pneumophila

• Conditional approaches (if atpH is essential):

  • Inducible promoter systems: Replace the native atpH promoter with an IPTG-inducible one, similar to the approach used for complementation strains in L. pneumophila studies

  • Temperature-sensitive alleles: Create conditional mutants that function at permissive temperatures only

• Knockdown approaches:

  • Antisense RNA: Express RNA complementary to atpH mRNA to inhibit translation

  • CRISPRi: Use catalytically dead Cas9 with guide RNAs targeting atpH

• Phenotypic analysis of mutants:

  • Growth curves: In standard media, water environments, and during infection

  • Transcriptomics: To identify compensatory gene expression changes

  • Infection models: Test replication in amoebae and macrophages at MOI 0.05 with CFU determination at various timepoints

• Complementation studies:

  • Trans-complementation: Express wild-type atpH from a plasmid with IPTG induction (0.2 mM IPTG for 4 hr at 37°C before infection)

  • Site-directed mutant complementation: Express atpH variants to identify critical residues