Recombinant Burkholderia vietnamiensis ATP synthase subunit b (atpF)

What is the function of ATP synthase subunit b (atpF) in Burkholderia vietnamiensis?

ATP synthase subunit b (atpF) in B. vietnamiensis is a critical component of the bacterial F-type ATP synthase complex, functioning within the F₀ sector of the enzyme. This protein contributes to the formation of the peripheral stalk that connects the membrane-embedded F₀ portion to the catalytic F₁ portion. The primary function of atpF is to help stabilize the stator portion of the ATP synthase, enabling the rotary mechanism that couples proton translocation across the membrane to ATP synthesis. The protein plays an essential role in energy production through oxidative phosphorylation, specifically in the conversion of proton motive force into ATP, a process vital for bacterial survival .

What is the molecular structure and composition of the recombinant atpF protein?

The recombinant B. vietnamiensis atpF protein consists of 156 amino acids with the following sequence:

MNLNATLFAQMVVFLVLAWFTMKFVWPPLINALDERSKKIADGLAAAEKGKAELDAAHKRVDQELAQARNDGQQRIADAEKRAQAVAEEIKANAQAEAARIVAQAKAEAEQQIVKARETLRGEVAALAVKGAEQILKREVDQTAHAQLLNQLKAEL

The protein has a UniProt ID of A4JA31 and is commonly expressed with an N-terminal His-tag to facilitate purification. The recombinant form maintains structural characteristics that allow it to interact with other ATP synthase components, featuring hydrophobic regions for membrane association and hydrophilic regions for stator assembly. The protein is typically produced as a lyophilized powder with greater than 90% purity as determined by SDS-PAGE .

How does atpF differ from atpD in the ATP synthase complex?

While both are components of the same ATP synthase complex, atpF and atpD serve distinct functions:

The atpD subunit is directly involved in the catalytic mechanism of ATP synthesis, containing conserved motifs critical for proton translocation and ATP synthesis, whereas atpF plays a more structural role in maintaining the integrity of the complex .

What are optimal expression systems for recombinant B. vietnamiensis atpF?

For efficient expression of recombinant B. vietnamiensis atpF, E. coli-based expression systems have proven most effective. The protein can be successfully expressed as a full-length construct (1-156 amino acids) with an N-terminal His-tag for purification purposes . While E. coli is the predominant system, other heterologous expression systems such as baculovirus-infected insect cells may also be considered for specific experimental requirements, similar to what has been observed with the related atpD protein.

For optimal expression in E. coli, consider the following methodological approach:

• Clone the atpF gene (Bcep1808_0111) into a suitable expression vector containing a strong promoter (T7 or tac) and N-terminal His-tag.

• Transform the construct into an E. coli expression strain (BL21(DE3) or derivatives).

• Grow cultures at 37°C until mid-log phase (OD₆₀₀ of 0.6-0.8).

• Induce protein expression with IPTG (0.1-1.0 mM) at reduced temperature (16-25°C) to enhance proper folding.

• Continue expression for 4-16 hours depending on protein stability and yield requirements.

This approach typically yields sufficient recombinant protein for downstream applications and structural studies .

What purification strategies yield the highest purity for recombinant atpF?

Purification of His-tagged recombinant atpF typically follows a multi-step chromatography approach:

• Initial Capture: Immobilized metal affinity chromatography (IMAC) using Ni-NTA or Co-NTA resins is the primary method for capturing His-tagged atpF from cellular lysates.

• Intermediate Purification: Ion exchange chromatography, particularly using Q-Sepharose for anion exchange, further removes contaminants based on charge differences.

• Polishing Step: Size exclusion chromatography (SEC) provides the final purification step to achieve >90% purity as verified by SDS-PAGE .

For membrane-associated proteins like atpF, addition of mild detergents (0.1-0.5% Triton X-100 or n-dodecyl β-D-maltoside) during extraction and early purification steps helps maintain protein solubility and native structure. The purified protein is typically formulated in Tris/PBS-based buffer containing 6% trehalose at pH 8.0 to maintain stability . This purification strategy is similar to methods used for the related atpD protein, which is typically purified using chromatography techniques and stored at -20°C or -80°C to maintain stability.

How should recombinant atpF be stored to maintain stability and activity?

Optimal storage conditions for recombinant atpF include:

• Short-term storage: Aliquots can be maintained at 4°C for up to one week without significant loss of integrity.

• Long-term storage: Store lyophilized powder or protein solutions at -20°C/-80°C.

• Buffer composition: Tris/PBS-based buffer with 6% trehalose at pH 8.0 provides optimal stability .

For reconstitution, the lyophilized protein should be dissolved in deionized sterile water to a concentration of 0.1-1.0 mg/mL. Addition of glycerol (final concentration of 5-50%, with 50% being standard) is recommended prior to aliquoting for long-term storage at -20°C/-80°C. Repeated freeze-thaw cycles should be avoided as they can significantly compromise protein structure and function .

How can recombinant atpF be utilized in structural biology studies?

Recombinant atpF serves as a valuable tool for structural biology investigations of the ATP synthase complex through several methodological approaches:

• Cryo-electron Microscopy (Cryo-EM): Purified atpF can be reconstituted with other ATP synthase components for structural determination of the intact complex, providing insights into stator assembly and stability.

• X-ray Crystallography: While challenging due to the partially hydrophobic nature of atpF, crystallographic studies can reveal atomic-level details of protein-protein interfaces within the stator region.

• NMR Spectroscopy: For studying dynamic interactions between atpF and other subunits, as well as conformational changes during ATP synthesis.

• Cross-linking and Mass Spectrometry: These techniques can map interaction surfaces between atpF and other ATP synthase components, helping elucidate the assembly mechanism of the complex.

These structural investigations are particularly valuable for understanding how the stator components resist the torque generated during the rotary catalytic mechanism, which is fundamental to ATP synthesis and hydrolysis processes .

What roles does atpF play in bacterial pathogenicity and potential antimicrobial targets?

The ATP synthase complex, including atpF, represents a potential target for antimicrobial development due to its essential role in bacterial energy metabolism. Several research avenues include:

• Virulence Connection: While not directly established for atpF, studies with related ATP synthase components suggest links to pathogenicity. For instance, mutations in homologs of the related atpD have been linked to resistance against aminoglycosides and fluoroquinolones in B. cepacia isolates.

• Inhibitor Development: Compounds that specifically target bacterial ATP synthase components could potentially disrupt energy metabolism. Drawing parallels from studies on mitochondrial ATP synthase, where compounds like (+)-epicatechin selectively inhibit ATP hydrolysis without affecting ATP synthesis , similar approaches could be explored for bacterial targets.

• Functional Assays: Recombinant atpF can be incorporated into functional assays to screen for compounds that disrupt ATP synthase assembly or stability, potentially leading to novel antimicrobial strategies targeting energy production in pathogenic Burkholderia species.

These applications are particularly relevant for B. vietnamiensis, which belongs to the B. cepacia complex (BCC) known to cause severe infections in cystic fibrosis patients.

How can atpF be used in studying bacterial bioenergetics?

Recombinant atpF provides researchers with a valuable tool for investigating bacterial energy transduction mechanisms through several methodological approaches:

• Reconstitution Studies: Purified atpF can be combined with other ATP synthase components in liposomes to study proton translocation and ATP synthesis in a controlled environment.

• Site-Directed Mutagenesis: Strategic mutations in atpF can help identify critical residues involved in stator assembly and function, providing insights into the coupling mechanism between proton flow and ATP synthesis.

• Comparative Bioenergetics: atpF can be used in comparative studies across different bacterial species to understand adaptive variations in ATP synthase structure and function.

• Bioenergetic Applications: The protein's role in proton translocation makes it relevant for bioenergy applications, such as optimizing microbial fuel cells or developing novel antimicrobial strategies targeting bacterial energy production.

These approaches contribute to our fundamental understanding of bacterial energy metabolism, which remains critical for identifying new therapeutic targets in pathogens like B. vietnamiensis.

How can researchers verify the functional integrity of recombinant atpF?

Verifying the functional integrity of recombinant atpF requires multiple complementary approaches:

• Structural Integrity Assessment:

  • Circular dichroism (CD) spectroscopy to verify secondary structure content

  • Thermal shift assays to assess protein stability

  • Limited proteolysis to confirm proper folding resistance

• Functional Verification:

  • Binding assays with other ATP synthase components (particularly the α and δ subunits)

  • In vitro reconstitution with other purified subunits to form partial or complete ATP synthase complexes

  • Proteoliposome reconstitution to measure ATP-dependent proton pumping activity

• Activity Validation:

  • ATP hydrolysis assays of reconstituted complexes containing atpF

  • Proton pumping assays using pH-sensitive fluorescent dyes

  • Complementation studies in atpF-deficient bacterial strains

This multi-faceted approach ensures that the recombinant protein maintains both structural and functional properties necessary for its biological role as part of the ATP synthase complex.

What are common challenges in expressing recombinant atpF and how can they be addressed?

Expression of recombinant atpF can present several challenges that researchers should anticipate and address:

Additionally, for proteins that prove particularly challenging, alternative expression systems such as baculovirus-infected insect cells (as used for the related atpD protein) may be considered . Implementing these strategies can significantly improve the quantity and quality of recombinant atpF obtained for downstream applications.

What controls are essential when studying atpF interactions with other ATP synthase components?

Robust experimental design for studying atpF interactions requires several critical controls:

• Negative Interaction Controls:

  • Non-interacting proteins of similar size/charge to rule out non-specific binding

  • Mutant atpF variants with disrupted binding interfaces

  • Competitively block interactions with peptides derived from interaction sites

• Positive Interaction Controls:

  • Known interaction partners (such as the δ subunit) with validated binding

  • Previously characterized protein-protein interactions within the ATP synthase complex

• Technical Controls:

  • Tag-only constructs to identify tag-mediated artifacts

  • Buffer-only conditions to establish baseline measurements

  • Concentration-matched samples to ensure comparable signal intensities

• Validation Through Multiple Methods:

  • Combine biophysical techniques (SPR, ITC, MST) with biochemical approaches (pull-downs, cross-linking)

  • Validate in vitro findings with in vivo approaches when possible

Implementing these controls ensures that observed interactions represent genuine biological phenomena rather than experimental artifacts, particularly important when reconstituting complex multi-protein assemblies like the ATP synthase.

How conserved is atpF across Burkholderia species and what does this reveal about evolutionary pressure?

Comparative analysis of atpF sequences across Burkholderia species reveals patterns of conservation that provide insights into evolutionary pressure on ATP synthase components:

The atpF gene has been used as a marker in phylogenetic analyses to distinguish B. vietnamiensis from other Burkholderia species, with its sequence divergence aiding in identifying pathogens such as members of the B. cepacia complex (BCC). This suggests sufficient variability to be taxonomically informative while maintaining functional constraints.

Conservation analysis typically reveals:

This evolutionary pattern makes atpF valuable for both taxonomic identification and functional studies across the Burkholderia genus, particularly for distinguishing closely related species within the clinically important B. cepacia complex.

Can atpF be used as a phylogenetic marker for bacterial identification?

The atpF gene has significant potential as a phylogenetic marker for bacterial identification, particularly within the Burkholderia genus:

• Taxonomic Resolution: The sequence divergence in atpF aids in distinguishing B. vietnamiensis from other Burkholderia species, making it useful for identifying pathogens within the B. cepacia complex (BCC).

• Methodological Approach:

  • PCR amplification of atpF using genus-specific primers

  • Sequence analysis and comparison to reference databases

  • Phylogenetic tree construction to determine species relationships

  • Combination with other marker genes (e.g., 16S rRNA, atpD) for multi-locus sequence typing

• Advantages Over Single-Gene Markers:

  • More discriminatory power than 16S rRNA for closely related species

  • Essential housekeeping function reduces likelihood of horizontal gene transfer

  • Evolutionary rate suitable for species-level resolution

• Applications in Environmental and Clinical Microbiology:

  • Identification of B. vietnamiensis strains in environmental samples

  • Discrimination between beneficial environmental isolates and clinically relevant strains

  • Tracking of Burkholderia species in plant growth-promoting rhizobacteria applications

This approach is particularly valuable for differentiating between beneficial environmental Burkholderia strains (like those with plant growth-promoting properties) and pathogenic isolates that cause infections in vulnerable populations.