Recombinant Parabacteroides distasonis ATP synthase subunit b (atpF)

What is the basic structure and function of P. distasonis ATP synthase subunit b (atpF)?

The ATP synthase subunit b (atpF) from Parabacteroides distasonis is a critical component of the F-type ATPase complex responsible for ATP production in this anaerobic gut bacterium. The protein consists of 166 amino acids with the sequence starting with "MSLLTPDSGLL..." and contains distinct hydrophobic and hydrophilic domains . The hydrophobic N-terminal region anchors the protein in the membrane, while the hydrophilic portion extends into the cytoplasm to interact with other ATP synthase components. Functionally, atpF serves as part of the peripheral stator stalk that connects the F₁ catalytic domain to the membrane-embedded F₀ motor domain, preventing rotation of the α₃β₃ hexamer during ATP synthesis .

How does P. distasonis atpF differ from other bacterial ATP synthase b subunits?

P. distasonis atpF shares structural similarities with other bacterial b subunits but contains unique sequence features reflecting its evolutionary adaptation within the Bacteroidota phylum. Comparative analysis shows that while the core function remains conserved, P. distasonis atpF exhibits distinct amino acid compositions particularly in the C-terminal region where it interacts with the delta subunit . Unlike some other bacterial species, P. distasonis ATP synthase appears to utilize a Na⁺-dependent mechanism rather than solely H⁺-dependent ATP synthesis based on homology to other Bacteroidetes ATP synthases . This adaptation may reflect the anaerobic gut environment where P. distasonis typically resides and potentially influences its energy metabolism under varying ion gradients.

What are the optimal expression systems for producing recombinant P. distasonis atpF?

Several expression systems have been successfully employed for recombinant production of P. distasonis atpF, each with specific advantages:

• Baculovirus expression system: Provides high yields of properly folded protein with minimal endotoxin contamination. This system has been used commercially to produce research-grade atpF protein with >85% purity .

• E. coli expression systems: Modified strains such as T7 Express lysY/Iq have been used for membrane protein expression. For optimal results, the atpF gene should be codon-optimized for E. coli expression and potentially fused to solubility-enhancing partners such as MBP (maltose-binding protein) to prevent inclusion body formation .

• Co-expression with chaperones: When expressing in E. coli, co-transformation with plasmids expressing chaperone proteins (DnaK, DnaJ, and GrpE) has been shown to substantially increase yields of difficult-to-express membrane proteins like ATP synthase components .

For challenging membrane protein expression, a comparative approach testing multiple expression vectors and conditions is recommended, with systematic optimization of induction temperature (typically 15-30°C), inducer concentration, and expression duration.

What purification strategies yield the highest purity and functional activity for recombinant atpF?

A multi-step purification protocol is recommended to obtain high-purity recombinant P. distasonis atpF suitable for structural and functional studies:

• Initial extraction: For membrane proteins like atpF, detergent-based extraction is essential. Common detergents include n-dodecyl-β-D-maltoside (DDM), Triton X-100, or CHAPS at concentrations just above their critical micelle concentration.

• Affinity chromatography: If expressed with affinity tags (His6, FLAG, or MBP), corresponding affinity chromatography provides effective initial purification. For MBP-fusion constructs, amylose resin has been effective, with elution using maltose-containing buffers .

• Ion exchange chromatography: Following initial purification, ion exchange chromatography (typically anion exchange using Q-Sepharose) further removes contaminants.

• Size exclusion chromatography: A final polishing step using size exclusion provides highest purity, separating monomeric protein from aggregates.

Throughout purification, maintaining the protein in buffers containing appropriate detergents and potentially phospholipids (POPC or E. coli total lipid extract) helps preserve native conformation and function. Protein quality should be assessed by SDS-PAGE (>85% purity) and potential activity assays such as reconstitution into liposomes followed by ATP hydrolysis/synthesis measurements .

How can researchers troubleshoot common issues in recombinant atpF production?

Experimental validation of troubleshooting approaches is essential using analytical techniques such as circular dichroism to assess secondary structure, size exclusion chromatography to evaluate oligomeric state, and reconstitution assays to verify functional activity .

How can recombinant P. distasonis atpF be used in structural biology studies?

Recombinant P. distasonis atpF provides valuable material for various structural biology approaches:

• X-ray crystallography: Highly purified atpF (>95%) can be used for crystallization trials, typically in the presence of lipids or detergent micelles to stabilize the hydrophobic regions. Molecular replacement using homologous structures from other bacterial ATP synthases can facilitate structure determination.

• Cryo-electron microscopy: atpF can be reconstituted with other ATP synthase components to study the complete complex structure. This approach is particularly valuable for membrane proteins as it avoids the need for crystallization.

• NMR spectroscopy: Isotopically labeled atpF (¹⁵N, ¹³C) can be produced in minimal media for solution NMR studies of the soluble domains or solid-state NMR of the full-length protein in membrane mimetics.

• Cross-linking studies: Chemical cross-linking combined with mass spectrometry can identify interaction interfaces between atpF and other ATP synthase subunits, particularly with subunit delta (atpH) .

When designing structural experiments, researchers should consider that the membrane-spanning N-terminal region may require specialized approaches compared to the soluble C-terminal domain, potentially warranting separate expression of these domains for certain applications .

What approaches can be used to study the ion specificity and energy transduction mechanisms involving P. distasonis atpF?

To investigate whether P. distasonis ATP synthase operates with Na⁺ or H⁺ specificity:

• Reconstitution studies: Purified recombinant atpF can be incorporated with other ATP synthase subunits into liposomes with controlled internal and external ion concentrations. ATP synthesis rates can be measured under varying Na⁺/H⁺ gradients to determine ion specificity .

• Site-directed mutagenesis: Key residues predicted to be involved in ion coordination can be mutated, and the effects on ion-dependent ATP synthesis/hydrolysis measured. This approach has been successful in other F-type ATP synthases to identify critical ion-binding residues.

• Isothermal titration calorimetry (ITC): This technique can measure binding affinities of different ions to the purified ATP synthase complex or subunits, providing thermodynamic data on ion preference.

• Electrophysiology techniques: Reconstituting the ATP synthase in planar lipid bilayers allows direct measurement of ion currents through the complex under varying conditions.

Given that P. distasonis inhabits the gut environment where ion concentrations may vary significantly, understanding its ATP synthase ion specificity could provide insights into how this organism adapts energetically to different microenvironments and how this might relate to host-microbe interactions in health and disease states .

How can researchers investigate the potential role of P. distasonis atpF in host-microbe interactions?

The ATP synthase components of P. distasonis may play roles beyond energy metabolism, particularly in host-microbe interactions:

• Immunological studies: Purified recombinant atpF can be used in stimulation assays with immune cells (dendritic cells, macrophages) to assess its immunomodulatory properties. Research has shown that bacterial ATP synthase components can sometimes act as pathogen-associated molecular patterns (PAMPs) or antigens recognized by the host immune system .

• Cross-reactivity analysis: The phenomenon observed where pre-existing antibodies target SARS-CoV-2 S2 protein has been linked to structural similarities with gut microbiota proteins. Similar approaches can investigate whether atpF shares epitopes with host proteins that might contribute to autoimmunity .

• Metagenomic association studies: Correlations between P. distasonis ATP synthase gene variants and host disease states can be analyzed using patient-derived metagenomic data, particularly in inflammatory bowel disease and Crohn's disease cohorts .

• In vivo colonization models: Wild-type versus ATP synthase-mutant P. distasonis strains can be compared for their ability to colonize gnotobiotic mice, providing insights into the importance of energy metabolism for gut colonization and persistence .

Research designs should account for potential functional differences between laboratory reference strains (like ATCC 8503) and patient-derived isolates, as genomic and functional heterogeneity within P. distasonis has been demonstrated .

What evidence exists for horizontal gene transfer involving P. distasonis atpF and related ATP synthase components?

Genomic analyses have revealed significant evidence of horizontal gene transfer (HGT) involving P. distasonis, including genes encoding energy metabolism components:

• DNA "bombardment" pattern: Comparative genomic analyses have demonstrated a striking pattern described as "systematic bombardment of Bacteroides DNA" into P. distasonis genomes. This includes exchange of numerous genetic elements, potentially affecting energy metabolism genes including ATP synthase components .

• Insertion analysis: Studies of P. distasonis isolates from patients with Crohn's disease identified distinctive genomic insertions shared with Bacteroides fragilis. These insertions were found in multiple independent clinical isolates, indicating their potential functional significance and transmission between gut bacteria .

• Phylogenetic incongruence: By constructing phylogenetic trees based on ATP synthase genes versus whole-genome data, researchers can identify instances where atpF and other ATP synthase genes show evolutionary histories inconsistent with species phylogeny, suggesting HGT events.

The organization of the ATP synthase operon in P. distasonis (rnfBCDGEA pattern) mirrors that found in several other Bacteroidetes species including Bacteroides vulgatus, Chlorobium species, and Porphyromonas uenonis, supporting the concept of conserved gene transfer within this bacterial group . These evolutionary events may contribute to functional adaptations of P. distasonis in different host environments.

How does P. distasonis atpF compare structurally and functionally across different clinical isolates?

Emerging research indicates significant strain variation among P. distasonis isolates that extends to energy metabolism components:

• Clade differentiation: Analysis of P. distasonis isolates from patients with digestive diseases has revealed the existence of at least two distinct clades of P. distasonis based on differences in carbohydrate surface composition and genomic features .

• Functional implications: These structural variations potentially impact ATP synthase components and may influence energy metabolism, affecting how different P. distasonis strains function as either commensals or pathobionts in the human gut .

• Comparative proteomics approach: To systematically investigate atpF variation, researchers can employ:

  • Multiple sequence alignment of atpF sequences from diverse isolates

  • Structural modeling to predict functional impacts of sequence variations

  • Recombinant expression of variant proteins to assess functional differences in ATP synthesis rates, ion specificity, and protein-protein interactions

The laboratory reference strain ATCC 8503 (commonly used for recombinant protein production) may not fully represent the diversity of clinically relevant P. distasonis strains. Researchers should consider including multiple clinical isolates when studying ATP synthase function in relation to disease associations .

What can sodium versus proton specificity in P. distasonis ATP synthase tell us about bacterial adaptation to the gut environment?

The ion specificity of ATP synthase represents an important adaptive feature for bacteria in different environments:

• Environmental adaptation: While most bacterial ATP synthases use H⁺ as the coupling ion, some bacteria, particularly those adapted to sodium-rich or anaerobic environments, have evolved Na⁺-dependent ATP synthases. The gut environment, where P. distasonis resides, has fluctuating ion concentrations that may favor adaptable energy metabolism systems .

• Experimental approach to determine specificity:

  • Purified recombinant atpF and other ATP synthase components can be reconstituted into liposomes

  • ATP synthesis/hydrolysis rates can be measured under varying Na⁺/H⁺ concentrations and gradients

  • Site-directed mutagenesis of predicted ion-coordinating residues can confirm the molecular basis of ion specificity

• Comparative analysis: Researchers should compare the putative ion-binding sites in P. distasonis atpF with those of well-characterized Na⁺-dependent ATP synthases (like that of Ilyobacter tartaricus) and H⁺-dependent ATP synthases (like E. coli). Key residues in the c-ring and a-subunit typically determine ion specificity .

Understanding the ion specificity of P. distasonis ATP synthase provides insights into how this organism has adapted to the gastrointestinal environment and may inform the development of targeted antimicrobials or probiotics that modulate gut microbiota energy metabolism .

How might P. distasonis ATP synthase components contribute to inflammatory bowel disease pathophysiology?

Emerging evidence suggests potential roles for P. distasonis ATP synthase components in inflammatory bowel disease (IBD) through several mechanisms:

• Immunogenic potential: Bacterial ATP synthase components can trigger immune responses. Studies have detected cross-reactive antibodies between gut microbiota proteins and viral proteins, suggesting that molecular mimicry involving bacterial proteins (potentially including ATP synthase components) may play a role in aberrant immune responses .

• Metabolic reprogramming: In Crohn's disease-associated fistulous tracts, clonal P. distasonis exhibits distinctive metabolic adaptations, potentially involving altered energy metabolism. The ATP synthase complex is central to energy production and may be involved in adaptation to the inflammatory environment .

• Experimental approaches to investigate this connection:

  • Compare ATP synthase gene expression and protein levels between P. distasonis strains from healthy individuals versus IBD patients

  • Assess immunogenicity of recombinant atpF in peripheral blood mononuclear cells from IBD patients versus healthy controls

  • Develop mouse models with colonization by wild-type versus ATP synthase-modified P. distasonis to assess effects on intestinal inflammation

The two distinct clades of P. distasonis identified in clinical studies may differ in their ATP synthase characteristics, potentially explaining differential associations with disease states versus protective effects .

What is the relationship between P. distasonis energy metabolism and its therapeutic effects in metabolic disorders?

P. distasonis has shown therapeutic potential in metabolic disorders, with its energy metabolism potentially playing a key role:

• Bile acid metabolism connection: P. distasonis has been linked to the production of non-12OH bile acids (like UDCA and LCA), which promote increased energy expenditure and thermogenesis. The ability of P. distasonis to produce these metabolites depends on its energy metabolism capabilities, in which ATP synthase plays a central role .

• Weight regulation effects: Studies have shown that depletion of P. distasonis and associated non-12OH bile acids results in reduced energy expenditure in weight-rebound mice. Supplementation with P. distasonis ameliorated weight regain by promoting thermogenesis .

• Mechanistic investigation approaches:

  • Compare ATP synthase activity and expression between P. distasonis in normal versus metabolically diseased states

  • Assess how manipulation of atpF and other ATP synthase genes affects P. distasonis metabolite production

  • Investigate correlations between ATP synthase gene variants and metabolic functions in clinical isolates

These findings suggest that the energy metabolism of P. distasonis, facilitated by its ATP synthase complex, is integrally linked to its beneficial effects on host metabolism, potentially through the production of specific bile acid metabolites that influence host energy expenditure .

How can recombinant P. distasonis atpF be used to develop targeted interventions for microbiome modulation?

Recombinant P. distasonis atpF has potential applications in developing targeted microbiome interventions:

• Diagnostic marker development: Antibodies against specific P. distasonis ATP synthase components could be developed to quantify and track this beneficial bacterium in patient samples. This would enable personalized microbiome assessments focusing on functional bacterial components rather than just taxonomic profiles .

• Targeted prebiotic development: Understanding the energy metabolism of P. distasonis, particularly its ATP synthase characteristics, could inform the development of prebiotics specifically designed to promote the growth of beneficial P. distasonis strains while limiting growth of pathogenic species .

• Vaccine adjuvant potential: Recombinant bacterial proteins, including ATP synthase components, have been investigated as potential vaccine adjuvants. P. distasonis atpF could be explored for its immunomodulatory properties to enhance vaccine responses or develop microbiota-based immunotherapies .

• Experimental design considerations:

  • Structure-function studies to identify immunologically active versus enzymatically functional domains

  • Animal models to assess safety and efficacy of atpF-based interventions

  • In vitro gut models to evaluate effects on complex microbial communities

Researchers should note that the aerotolerant nature of P. distasonis (unusual for an anaerobe) may be related to its energy metabolism adaptations, potentially involving its ATP synthase components. This characteristic may make P. distasonis particularly suitable for probiotic development, as it may survive better during production and delivery processes compared to strict anaerobes .

What mass spectrometry approaches are most effective for studying post-translational modifications of P. distasonis atpF?

Advanced mass spectrometry techniques provide powerful tools for characterizing post-translational modifications (PTMs) of recombinant and native P. distasonis atpF:

• Sample preparation optimization:

  • Filter-aided sample preparation (FASP) protocol using devices like Microcon PL-10 filters

  • Reduction with 10 mM DTT at 37°C for 30 minutes followed by alkylation with 30 mM iodoacetamide at 25°C for 45 minutes in darkness

  • Digestion with trypsin at a 1:50 enzyme-to-protein ratio at 37°C for 12 hours after buffer exchange

• MS/MS analysis approaches:

  • High-resolution LC-MS/MS using instruments such as Orbitrap or QTOF systems

  • Multiple reaction monitoring (MRM) for targeted quantification of specific modified peptides

  • Electron transfer dissociation (ETD) or electron capture dissociation (ECD) fragmentation methods which better preserve labile PTMs compared to collision-induced dissociation

• Data analysis strategies:

  • Open search approaches to identify unexpected modifications

  • Site-specific quantification using extracted ion chromatograms of modified versus unmodified peptides

  • Comparison of PTM profiles between recombinant protein and native protein isolated from P. distasonis cultures

These techniques can reveal modifications that affect atpF function, stability, or interactions with other ATP synthase components, providing insights into regulatory mechanisms affecting bacterial energy metabolism under different environmental conditions .

What advanced biophysical methods can characterize the interactions between atpF and other ATP synthase components?

Several sophisticated biophysical techniques can elucidate the molecular interactions within the ATP synthase complex:

• Surface plasmon resonance (SPR):

  • Immobilize purified recombinant atpF on a sensor chip

  • Measure binding kinetics with other purified ATP synthase subunits in real-time

  • Determine association/dissociation rates and binding affinities under varying conditions (pH, ion concentrations)

• Hydrogen-deuterium exchange mass spectrometry (HDX-MS):

  • Map protein-protein interaction interfaces by identifying regions with decreased deuterium uptake when complexed with binding partners

  • Follow conformational changes in atpF under different functional states of the ATP synthase complex

  • Requires no modification of proteins and can be performed under near-native conditions

• Förster resonance energy transfer (FRET):

  • Engineer atpF and potential interaction partners with appropriate fluorophores

  • Measure energy transfer efficiency to determine proximity and orientation of proteins within the complex

  • Can be performed in reconstituted systems or potentially in live bacterial cells

• Native mass spectrometry:

  • Analyze intact protein complexes under non-denaturing conditions

  • Determine stoichiometry and stability of subcomplexes involving atpF

  • Characterize the complete assembly pathway of the ATP synthase complex

These methods provide complementary information about the structural organization and dynamic interactions within the ATP synthase complex, helping to elucidate how P. distasonis optimizes its energy metabolism for survival in the competitive gut environment .

How might genetic manipulation of P. distasonis atpF advance our understanding of its role in health and disease?

Genetic engineering approaches offer promising avenues to elucidate atpF function:

• CRISPR-Cas9 genome editing:

  • Development of targeted mutation systems for P. distasonis

  • Introduction of point mutations in key functional residues of atpF

  • Creation of conditional knockdown strains to study atpF essentiality

• Reporter systems:

  • Fusion of fluorescent or luminescent reporters to atpF to monitor expression and localization

  • Development of biosensors to measure ATP synthase activity in live cells

  • Analysis of atpF expression under different environmental conditions relevant to the gut microenvironment

• Heterologous expression:

  • Complementation studies in other bacterial species with atpF mutations

  • Expression of modified versions of atpF to assess functional conservation

  • Investigation of chimeric proteins combining domains from different bacterial ATP synthases

• In vivo colonization models:

  • Colonization of germ-free mice with wild-type versus atpF-modified P. distasonis

  • Assessment of competitive fitness in complex microbial communities

  • Analysis of host physiological responses to altered P. distasonis energy metabolism

These approaches would provide mechanistic insights into how P. distasonis ATP synthase contributes to bacterial fitness in the gut and influences host physiology in health and disease contexts .

What are the emerging research questions regarding P. distasonis ATP synthase in the context of microbiome-based therapeutics?

Several critical research questions emerge at the intersection of P. distasonis ATP synthase biology and therapeutic applications:

• Strain-specific functional variations:

  • How do ATP synthase components vary between beneficial versus potentially pathogenic P. distasonis strains?

  • Can specific atpF variants serve as biomarkers for functionally distinct P. distasonis populations?

  • Do genetic variations in ATP synthase genes correlate with therapeutic efficacy in metabolic disorders?

• Environmental adaptation mechanisms:

  • How does P. distasonis ATP synthase activity respond to changing gut conditions (pH, oxygen tension, nutrient availability)?

  • What regulatory mechanisms control ATP synthase expression in different microenvironments?

  • How do interactions with host factors or other microbiota influence P. distasonis energy metabolism?

• Translational research opportunities:

  • Can small molecule modulators of P. distasonis ATP synthase selectively promote beneficial strains?

  • How might dietary components influence P. distasonis ATP synthase activity and associated metabolite production?

  • Could engineered P. distasonis with modified ATP synthase serve as next-generation probiotics with enhanced therapeutic properties?

Addressing these questions will require interdisciplinary approaches combining microbiology, biochemistry, structural biology, and systems biology in the context of host-microbe interactions .

What systems biology approaches could integrate ATP synthase function with broader P. distasonis metabolic networks?

Comprehensive systems biology approaches can contextualize ATP synthase function within P. distasonis metabolism:

These systems-level approaches would provide a comprehensive understanding of how ATP synthase functions within the broader metabolic network of P. distasonis and how this relates to its roles in maintaining gut homeostasis and influencing host health .

Understanding these complex interactions would enable more rational design of microbiome-based interventions targeting P. distasonis for therapeutic applications in gastrointestinal and metabolic diseases .