Recombinant Yersinia pestis ATP synthase subunit b (atpF)

What is the ATP synthase subunit b (atpF) in Yersinia pestis and what is its role in bacterial metabolism?

ATP synthase subunit b is a critical component of the F₀F₁-ATP synthase complex in Y. pestis, the causative agent of plague. This protein serves as part of the peripheral stalk (or stator) that connects the membrane-embedded F₀ domain to the catalytic F₁ domain. The primary function of subunit b is to prevent rotation of the α₃β₃ hexamer during ATP synthesis, thus enabling the rotational catalysis mechanism that converts the proton motive force into chemical energy.

In Y. pestis metabolism, ATP synthase plays an essential role in energy production, particularly during aerobic respiration. The bacterium must adapt to diverse environmental conditions (26°C in the flea vector and 37°C in mammalian hosts), requiring flexible energy metabolism. The ATP synthase complex also contributes to maintaining intracellular pH homeostasis, critical for the function of numerous cellular processes during infection.

How does the structure of Y. pestis atpF relate to homologous proteins in other systems?

Research has established striking homology between components of the ATP synthase complex and the bacterial flagellar motor (BFM). Specifically, the ATP synthase subunit b (atpF product) shows significant homology to FliH of the Type 3 Secretion System (T3SS) export apparatus . This homology extends beyond sequence similarity to include conserved structural features and interaction patterns.

Most notably, gene order (synteny) is remarkably conserved between these systems. The gene order of fliHIJ in flagellar systems precisely matches the F-ATPase gene order of b-δ-α-γ . This deep conservation appears to date back billions of years, potentially predating the Last Universal Common Ancestor (LUCA) . The conservation suggests fundamental functional constraints that have maintained these relationships throughout bacterial evolution.

The structural similarities between atpF and FliH provide compelling evidence for their evolutionary relationship and suggest functional parallels between ATP synthesis and the protein export mechanisms of the flagellar system.

What experimental evidence supports the homology between atpF and flagellar export apparatus components?

Several lines of experimental evidence support the homology between Y. pestis atpF and components of the flagellar export apparatus:

• Sequence analysis: Computational studies have identified significant sequence similarities between atpF and FliH across diverse bacterial species .

• Structural similarities: Both proteins form elongated structures with similar domain organization, despite functioning in different cellular contexts.

• Interaction patterns: The interactions between atpF and other ATP synthase components mirror those between FliH and other flagellar proteins. For example, FliH interacts with FliI (homologous to F₁-α/β) and FliJ (homologous to F₁-γ) .

• Gene synteny: Perhaps the most compelling evidence is the conservation of gene order. The fliHIJ gene order in flagellar systems matches the b-δ-α-γ order in F-ATPase systems . This synteny has been maintained over vast evolutionary distances, suggesting functional significance.

• Yeast two-hybrid studies: Protein-protein interaction studies using the yeast two-hybrid system have identified similar interaction networks between these homologous components .

These multiple lines of evidence collectively provide robust support for the evolutionary relationship between these seemingly distinct molecular machines.

What expression systems are most effective for recombinant Y. pestis atpF production?

While specific protocols for Y. pestis atpF expression are not widely documented, several systems have proven effective for similar membrane proteins and other Y. pestis recombinant proteins:

• Plant-based expression systems: A deconstructed tobacco mosaic virus (TMV)-based system in Nicotiana benthamiana has demonstrated "very rapid and extremely high levels of expression" for Y. pestis antigens F1, V, and F1-V, achieving yields of 1-2 mg/g of fresh leaf weight . This approach represents an "inexpensive and scalable alternative to common expression systems" .

• E. coli expression systems: For membrane proteins like atpF, specialized E. coli strains such as C41(DE3) or C43(DE3) are often preferred. These strains are engineered to tolerate membrane protein overexpression.

• Cell-free expression systems: These can be advantageous for membrane proteins, allowing direct incorporation into nanodiscs or liposomes during synthesis.

For optimal expression, sequence optimization may be necessary, as was implemented for other Y. pestis proteins where 21.5% of native codons were changed to host-preferred codons . Additional optimizations might include removing potential methylation sites, putative splicing sites, polyadenylation signals, and mRNA destabilizing sequences .

What purification strategy yields the highest purity and functional integrity of recombinant atpF?

A multi-step purification approach is recommended for obtaining high-purity, functionally intact Y. pestis atpF:

For Y. pestis F1 and V antigens expressed in plants, a purification scheme including ammonium sulfate precipitation, hydrophobic interaction chromatography, and anion exchange chromatography yielded >90% purity . Similar multi-step approaches would be applicable to atpF, with modifications for membrane protein handling.

Throughout purification, maintaining an appropriate detergent concentration above the critical micelle concentration is essential for preventing aggregation and preserving native structure. Final preparation should be stored with stabilizing agents such as glycerol to maintain functional integrity.

What analytical methods best confirm the structural integrity of purified recombinant atpF?

Multiple complementary analytical techniques should be employed to verify the structural integrity of purified recombinant Y. pestis atpF:

• Circular Dichroism (CD) Spectroscopy: Provides information on secondary structure content to confirm proper folding.

• Fluorescence Spectroscopy: Intrinsic tryptophan fluorescence can indicate tertiary structure integrity.

• Thermal Shift Assays: Measures protein stability and can be used to optimize buffer conditions.

• Size Exclusion Chromatography coupled with Multi-Angle Light Scattering (SEC-MALS): Determines oligomerization state and homogeneity.

• Mass Spectrometry:

  • Intact mass analysis to confirm correct processing

  • Peptide mapping to verify sequence

  • Hydrogen-deuterium exchange to assess structural dynamics

• Functional Assays:

  • ATP synthase reconstitution to measure function

  • Binding assays with interaction partners (e.g., δ subunit)

• Negative Stain Electron Microscopy: Visualizes protein shape and aggregation state.

• Native PAGE: Assesses homogeneity and oligomeric state under non-denaturing conditions.

These methods collectively provide a comprehensive assessment of structural integrity at different levels of protein organization, ensuring that the recombinant atpF maintains its native conformation suitable for subsequent structural and functional studies.

How can structural studies of Y. pestis atpF contribute to understanding ATP synthase assembly and function?

Structural studies of Y. pestis atpF can provide several critical insights into ATP synthase assembly and function:

Appropriate methodologies include cryo-electron microscopy for whole-complex studies, X-ray crystallography or NMR for domain-specific analyses, and molecular dynamics simulations to investigate dynamic aspects of function.

What methodologies best examine the functional relationship between atpF and the flagellar protein FliH?

To investigate the functional relationship between atpF and FliH, researchers should employ these methodological approaches:

• Complementation Studies: Genetic experiments where atpF is expressed in fliH mutants (or vice versa) can test functional interchangeability. This approach can identify whether these proteins retain functional overlap despite evolutionary divergence.

• Domain Swapping Experiments: Creating chimeric proteins that combine domains from atpF and FliH can determine which regions retain functional equivalence and which have evolved specialized roles.

• Protein-Protein Interaction Analysis:

  • Yeast two-hybrid screening to compare interaction partners

  • Pull-down assays with tagged recombinant proteins

  • Surface plasmon resonance to measure binding kinetics

• Comparative Structural Biology:

  • Hydrogen-deuterium exchange mass spectrometry to identify structurally similar regions

  • Cross-linking mass spectrometry to map interaction interfaces

  • Comparative modeling based on experimental structures

• Evolutionary Analysis:

  • Synteny mapping across diverse bacterial phyla

  • Phylogenetic analyses to reconstruct the evolutionary history

  • Identification of co-evolving residue networks

These approaches can collectively reveal whether functional parallels exist in how these proteins interact with their respective systems, potentially identifying conserved mechanistic principles that span ATP synthesis and protein export processes.

What implications does the evolutionary relationship between ATP synthase and flagellar components have for bacterial physiology?

The evolutionary relationship between ATP synthase and flagellar components has profound implications for understanding bacterial physiology:

• Conservation of Energy Coupling Mechanisms: The homology suggests ancient and fundamental mechanisms for coupling energy (ATP hydrolysis/synthesis) to mechanical work (rotation/protein export) that have been conserved across diverse bacterial functions .

• Co-regulation Possibilities: The conserved gene order (synteny) between fliHIJ and b-δ-α-γ suggests potential for co-regulation or coordinated expression, which could allow bacteria to simultaneously modulate energy production and motility in response to environmental conditions.

• Shared Chaperone Functions: Both systems involve protein assembly processes, suggesting potential overlap in chaperone functions or quality control mechanisms.

• Evolutionary Adaptation: The divergence of these systems demonstrates how bacteria can repurpose fundamental molecular machinery for new functions while maintaining core mechanistic principles.

• Drug Target Implications: Understanding these relationships might enable development of dual-targeting antimicrobials that simultaneously affect both energy metabolism and pathogenicity functions.

• Assembly Mechanisms: The structural similarities suggest conserved principles in how complex multi-protein machines are assembled in bacterial systems.

This relationship represents one of the most compelling examples of how complex molecular machines have evolved from common ancestral components, providing insight into the modular nature of bacterial molecular evolution.

How does atpF contribute to Y. pestis pathogenesis and virulence?

While atpF is not a classical virulence factor, it contributes significantly to Y. pestis pathogenesis through several mechanisms:

• Energy Production for Virulence Factor Expression: ATP synthesis is critical for powering the expression and function of established virulence determinants such as the Yersinia outer proteins (Yops) and the Type III Secretion System (T3SS).

• Adaptation to Host Environments: During infection, Y. pestis transitions between different host environments (flea vector at 26°C and mammalian host at 37°C). ATP synthase activity is crucial for adapting to these changing energy demands.

• Stress Response: During infection, Y. pestis encounters various stressors including nutrient limitation, oxidative stress, and host immune responses. Efficient energy metabolism supported by ATP synthase becomes critical for bacterial survival under these conditions.

• pH Homeostasis: ATP synthase contributes to maintaining intracellular pH, which is essential for the function of numerous virulence-associated proteins.

• Relationship to T3SS Components: The homology between ATP synthase components and the flagellar/T3SS apparatus suggests potential functional overlaps that may be significant for pathogenesis, as the T3SS is essential for Y. pestis virulence.

Understanding these contributions is important for comprehensively mapping the metabolic requirements for Y. pestis pathogenesis.

Can recombinant atpF serve as a diagnostic marker for Y. pestis infection?

Recombinant Y. pestis atpF has potential utility as a diagnostic marker, though with important considerations:

Advantages as a diagnostic target:

• Present in all Y. pestis strains due to its essential metabolic function

• Relatively conserved sequence allows for specific detection

• Expression likely maintained during different stages of infection

Methodological approaches for diagnostic applications:

• Antibody-based detection:

  • ELISA using anti-atpF antibodies to detect bacterial components in clinical samples

  • Immunohistochemistry for tissue samples

  • Lateral flow assays for point-of-care diagnostics

• Nucleic acid-based detection:

  • PCR amplification of atpF gene sequences

  • LAMP (Loop-mediated isothermal amplification) for field-deployable diagnostics

  • Multiplex assays combining atpF with established targets like caf1 (F1 antigen gene)

• Mass spectrometry:

  • Targeted identification of atpF peptides in clinical samples

Limitations and considerations:

• Lower abundance compared to capsular antigens like F1

• Not secreted, requiring bacterial lysis for detection

• Potential cross-reactivity with ATP synthase components from other bacteria

• Current diagnostic approaches for plague focus on established markers like F1 antigen

For optimal diagnostic value, atpF would likely serve best as part of a multi-target approach rather than as a standalone marker.

What structural features of atpF could be exploited for developing targeted antimicrobials?

Several structural features of Y. pestis atpF present potential opportunities for targeted antimicrobial development:

• Protein-Protein Interaction Interfaces: The interaction between atpF and other ATP synthase components (particularly the δ subunit) represents a potential target. Small molecules or peptides that disrupt these interactions could inhibit ATP synthase assembly and function.

• Membrane-Association Domains: Compounds that interfere with the membrane association of atpF could destabilize the entire ATP synthase complex.

• Species-Specific Structural Elements: Detailed structural analysis may reveal Y. pestis-specific features that could be selectively targeted to minimize effects on host ATP synthase.

• Dynamic Regions: Areas of atpF that undergo conformational changes during ATP synthesis could be locked in non-functional states by appropriate inhibitors.

• Dual-Targeting Potential: Given the homology between ATP synthase and flagellar/T3SS components , there may be opportunities to design molecules that simultaneously target both systems, potentially increasing efficacy and reducing resistance development.

Drug development approaches could include:

• Structure-based virtual screening against identified target sites

• Fragment-based drug discovery to identify initial chemical scaffolds

• Peptide mimetics designed to compete with natural binding partners

• Allosteric inhibitors that alter conformational dynamics

Challenges include achieving selectivity against mammalian ATP synthase and ensuring sufficient membrane permeability to reach the target.

What are the critical considerations when designing experiments to study atpF interactions with other ATP synthase components?

When studying atpF interactions with other ATP synthase components, researchers should address these critical considerations:

• Protein Expression and Purification:

  • Expression systems must maintain the native structure of membrane proteins

  • Detergent selection is crucial as it replaces the natural lipid environment

  • Consider co-expression of interacting partners to stabilize complexes

  • Purification conditions must preserve weak or transient interactions

• Interaction Detection Methods:

  • In vitro methods: Surface plasmon resonance, isothermal titration calorimetry, and microscale thermophoresis require purified components but provide quantitative binding parameters

  • Cellular methods: FRET, BiFC, and PLA can detect interactions in cellular contexts but may have lower resolution

  • High-throughput methods: Yeast two-hybrid can screen multiple interactions but may produce false positives

• Experimental Conditions:

  • pH and ionic strength significantly affect membrane protein interactions

  • Temperature conditions should reflect physiological relevance (26°C for flea environment, 37°C for mammalian host)

  • Lipid composition may influence membrane protein association

• Controls and Validation:

  • Include both positive controls (known interactions) and negative controls

  • Validate interactions using multiple independent methods

  • Confirm specificity with competition experiments

• Structural Considerations:

  • Account for conformational changes that may occur during ATP synthesis

  • Consider dynamic versus static interaction interfaces

  • Evaluate potential effects of tags or fusion proteins on interactions

These considerations help ensure reliable and physiologically relevant results when investigating the complex interaction network of ATP synthase components.

What genetic approaches are most effective for studying atpF function in Y. pestis?

Several genetic approaches offer effective strategies for studying atpF function in Y. pestis:

Challenges specific to Y. pestis include biosafety considerations (requiring BSL-3 facilities for virulent strains) and the temperature-dependent expression of virulence factors, which may necessitate comparing phenotypes at both 26°C and 37°C.

How can researchers effectively study the impact of atpF mutations on Y. pestis virulence?

To effectively study the impact of atpF mutations on Y. pestis virulence, researchers should employ a comprehensive approach:

• Strategic Mutation Design:

  • Focus on residues conserved across Y. pestis strains but divergent from host homologs

  • Target regions implicated in protein-protein interactions

  • Create mutations with varying severity (conservative substitutions to deletions)

  • Consider temperature-sensitive mutations to study function during host transition

• In Vitro Phenotypic Characterization:

  • Growth curves under various conditions (temperature, pH, nutrient limitation)

  • ATP synthesis assays to quantify functional impact

  • Stress response to relevant host conditions (oxidative stress, antimicrobial peptides)

  • Type III secretion system function, as this is critical for virulence

• Cellular Infection Models:

  • Macrophage infection and survival assays

  • Assessment of immune response modulation

  • Monitoring of Y. pestis intracellular trafficking

  • Human monocyte response, as these cells differentiate into dendritic cells upon Y. pestis infection

• Animal Models with Appropriate Controls:

  • Mouse pneumonic and bubonic plague models

  • Monitoring of bacterial dissemination and tissue burden

  • Survival curves and time-to-death analyses

  • Complementation with wild-type atpF to confirm phenotype specificity

• Immune Response Evaluation:

  • Cytokine profiles during infection

  • Neutrophil recruitment and function

  • T cell responses to Y. pestis antigens

  • Antibody production against bacterial components

• Combination with Other Virulence Factor Mutations:

  • Assess potential synergistic effects with established virulence factor mutations

  • Create double mutants to uncover functional relationships

These approaches provide complementary insights into how atpF function contributes to the complex pathogenesis of Y. pestis, while appropriate controls ensure that observed phenotypes are specifically attributable to atpF mutations rather than secondary effects.