Recombinant Prosthecochloris vibrioformis ATP synthase subunit b (atpF)

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

The ATP synthase subunit b in P. vibrioformis is a critical component of the peripheral stalk, connecting the membrane-embedded FO domain to the catalytic F1 domain. Based on comparative analysis with other bacterial F-type ATP synthases, this subunit forms part of the stationary elements that prevent rotation of the catalytic α3β3 hexamer during ATP synthesis or hydrolysis.

How does Prosthecochloris vibrioformis differ from other model organisms for ATP synthase studies?

P. vibrioformis belongs to the green sulfur bacteria (GSB), characterized by their ability to perform anoxygenic photosynthesis and nitrogen fixation . Unlike commonly studied organisms such as E. coli or mitochondria, P. vibrioformis has adapted to thrive in hydrogen sulfide-rich environments, hot spring sediments, and even coral skeletons .

These adaptations have shaped its energy metabolism, including potential modifications to its ATP synthase for operation under anaerobic, sulfide-rich conditions. The nonmotile nature and spherical/ovoid morphology of Prosthecochloris cells may also influence the organization of bioenergetic complexes within their membranes. With a genome of moderate complexity (2,103 protein-coding genes, 52.1% GC content) , P. vibrioformis offers a manageable system for comparative bioenergetics studies.

What expression systems have proven most effective for recombinant P. vibrioformis atpF?

While the search results don't specifically address expression systems for P. vibrioformis atpF, lessons from other membrane protein studies suggest several viable approaches:

For functional studies, co-expression with partner subunits may enhance stability and proper folding, as demonstrated in studies of ATP synthase complexes from other organisms. The inclusion of appropriate lipids during expression and purification is often critical for maintaining native-like behavior of membrane proteins like atpF.

How can researchers verify the correct folding of recombinant atpF?

Verifying proper folding of recombinant atpF requires multiple complementary approaches:

• Biophysical characterization:

  • Circular dichroism (CD) spectroscopy to assess secondary structure

  • Thermal shift assays to determine protein stability

  • Size exclusion chromatography to confirm monodispersity

• Structural integrity:

  • Limited proteolysis to identify well-folded domains resistant to digestion

  • Intrinsic fluorescence spectroscopy to probe tertiary structure

  • Native PAGE to assess oligomeric state

• Functional validation:

  • Binding assays with known interaction partners (e.g., other ATP synthase subunits)

  • Reconstitution with partner subunits to assess complex formation

  • Complementation assays in deletion strains

Similar approaches have been used to verify proper folding of ATP synthase subunits in organisms like Mycobacterium, where subunit interactions were critical for complex stability .

How do the unique ecological adaptations of P. vibrioformis influence the structure-function relationship of its atpF subunit?

P. vibrioformis has adapted to thrive in environments including hydrogen sulfide-rich mud and anaerobic zones of coral skeletons , which likely imposes unique constraints on its ATP synthase. The atpF subunit, as part of the peripheral stalk, may exhibit adaptations to maintain stability and function under these conditions.

Comparative analysis between coral-associated Prosthecochloris (CAP) and non-CAP clades has revealed specialized metabolic adaptations , suggesting that energy-converting complexes like ATP synthase might similarly display habitat-specific modifications. For instance, the presence of sulfide in the natural habitat may necessitate protective mechanisms against sulfide-mediated damage to the ATP synthase complex.

Researchers might investigate:

• Unique residue compositions conferring resistance to reactive sulfur species

• Specific structural elements enhancing stability under low oxygen tensions

• Adaptations facilitating interaction with photosynthetic electron transport components

What experimental approaches can elucidate the interaction between atpF and other ATP synthase subunits in P. vibrioformis?

Understanding subunit interactions requires multiple complementary approaches:

• Co-immunoprecipitation studies:

  • Similar to approaches used with the Rnf complex , develop antibodies against atpF

  • Identify co-precipitating partners through immunoblotting or mass spectrometry

  • Verify specific interactions through reciprocal pull-down experiments

• Cross-linking mass spectrometry:

  • Use chemical cross-linkers of defined length to capture interacting regions

  • Identify cross-linked peptides through LC-MS/MS analysis

  • Map interaction interfaces at residue-level resolution

• Structural biology approaches:

  • Single-particle cryo-EM of reconstituted complexes

  • Co-crystallization of interacting domains

  • Hydrogen-deuterium exchange mass spectrometry to map interaction interfaces

In mycobacterial ATP synthases, critical interactions between the α subunit C-terminal domain and the γ subunit were identified through structural and mutational studies . Similar approaches could reveal the specific interaction network involving atpF in P. vibrioformis.

How might post-translational modifications affect the function of P. vibrioformis atpF?

Although the search results don't specifically address post-translational modifications (PTMs) of P. vibrioformis atpF, membrane proteins in bacteria can undergo various modifications that affect their function:

To investigate the role of PTMs:

• Compare PTM profiles between native and recombinant proteins

• Generate site-directed mutants at modified positions

• Assess the impact on assembly, stability, and activity

In mycobacterial ATP synthases, regulatory mechanisms involving protein-protein interactions have been identified , suggesting that PTMs might similarly play roles in modulating P. vibrioformis ATP synthase activity.

What role might atpF play in the regulation of ATP hydrolysis in P. vibrioformis?

Based on studies of ATP hydrolysis regulation in mycobacteria, where the α subunit C-terminal domain (αCTD) interacts with the γ subunit to inhibit ATP hydrolysis , atpF in P. vibrioformis might contribute to similar regulatory mechanisms.

As part of the peripheral stalk, atpF connects the membrane-embedded FO domain with the catalytic F1 domain, potentially transmitting conformational changes that influence catalytic activity. In mycobacteria, deletion of regulatory elements like αCTD enhanced ATP hydrolysis by 32-fold , demonstrating the importance of structural elements in regulating enzymatic activity.

To investigate regulatory roles of atpF:

• Generate truncation variants to identify domains involved in regulation

• Perform site-directed mutagenesis of residues at potential regulatory interfaces

• Measure ATP synthesis and hydrolysis activities in reconstituted systems

How does the evolutionary relationship between different Prosthecochloris strains reflect in their atpF sequences?

Comparative genomic analysis between coral-associated Prosthecochloris (CAP) and non-CAP clades has revealed specialized metabolic capacities and adaptations to different ecological niches . This evolutionary divergence likely extends to their ATP synthases, including the atpF subunit.

Researchers might examine:

• Sequence conservation patterns across Prosthecochloris strains

• Correlation between atpF sequence variations and habitat-specific adaptations

• Evidence of horizontal gene transfer affecting ATP synthase genes

In the CAP clade, mobile genetic elements (MGEs) have been found to play an important role in evolutionary diversification , suggesting that ATP synthase genes might similarly be influenced by horizontal gene transfer events that contribute to habitat-specific adaptations.

What purification strategies yield the highest purity and stability for recombinant P. vibrioformis atpF?

Purifying membrane proteins like atpF requires specialized approaches:

• Solubilization optimization:

  • Screen multiple detergents (DDM, LMNG, digitonin) at various concentrations

  • Consider native nanodiscs or SMALPs for detergent-free extraction

  • Include stabilizing lipids based on the native membrane composition

• Chromatography strategy:

  • Initial IMAC purification exploiting affinity tags

  • Ion exchange chromatography to remove contaminants

  • Size exclusion chromatography as a final polishing step

• Stability enhancement:

  • Addition of specific lipids based on native membrane composition

  • Inclusion of stabilizing additives (glycerol, arginine, specific salts)

  • Storage at appropriate temperature with cryoprotectants

This systematic approach has proven successful for other membrane proteins and should be optimized specifically for P. vibrioformis atpF.

What are the most reliable methods for assessing atpF integration into functional ATP synthase complexes?

Since atpF functions as part of the ATP synthase complex, assessing its functional integration requires specialized approaches:

• Biochemical methods:

  • Blue native PAGE to visualize intact complexes

  • Co-immunoprecipitation with antibodies against different subunits

  • Size exclusion chromatography to analyze complex formation

• Functional assays:

  • ATP synthesis activity in reconstituted proteoliposomes

  • Proton pumping measured with pH-sensitive fluorescent dyes

  • ATP-dependent proton translocation assays

• Structural validation:

  • Negative-stain electron microscopy of purified complexes

  • Single-particle cryo-EM analysis

  • Cross-linking mass spectrometry to verify subunit interactions

Similar approaches have been used to study ATP synthase complexes from mycobacteria, where the interaction between different subunits was critical for complex stability and function .

How can researchers design effective site-directed mutagenesis experiments to probe atpF function?

Strategic site-directed mutagenesis can provide valuable insights into structure-function relationships:

• Target selection strategies:

  • Conserved residues identified through multiple sequence alignment

  • Charged residues at predicted subunit interfaces

  • Residues in predicted membrane-spanning regions

• Mutation design principles:

  • Conservative substitutions to probe specific interactions

  • Charge reversal to disrupt salt bridges

  • Alanine scanning to identify functionally important residues

• Functional assessment:

  • Complex assembly efficiency

  • ATP synthesis/hydrolysis rates

  • Stability measurements under varying conditions

In mycobacterial ATP synthases, specific residues in the α subunit (αE534, αE536, αK539, αR541, and αK542) interact with the γ subunit (γE207, γE209, and γE213) to regulate ATPase activity . Similar interaction interfaces involving atpF could be identified and characterized through systematic mutagenesis.

What techniques are available for studying the topology and membrane insertion of P. vibrioformis atpF?

Understanding membrane topology is crucial for membrane proteins like atpF:

• Experimental approaches:

  • Cysteine scanning mutagenesis coupled with accessibility assays

  • Fluorescence protease protection assays

  • Site-specific labeling followed by proteolytic digestion

• Protein engineering strategies:

  • Fusion with topology reporter proteins (PhoA, GFP)

  • Introduction of glycosylation sites as topological markers

  • Epitope insertion for antibody accessibility studies

• Computational prediction:

  • Transmembrane segment prediction algorithms

  • Hydropathy analysis

  • Evolutionary conservation mapping

For structural context, researchers can compare with known structures of ATP synthase b subunits from other organisms, while accounting for potential unique features of the P. vibrioformis protein.

What structural biology techniques are most appropriate for studying recombinant P. vibrioformis atpF?

Different structural techniques offer complementary insights:

• Cryo-electron microscopy:

  • Particularly suitable for membrane protein complexes

  • Can capture different conformational states

  • Has successfully resolved ATP synthase structures from various organisms

• X-ray crystallography:

  • Challenging for membrane proteins but possible with appropriate conditions

  • May require lipidic cubic phase or bicelle crystallization

  • Could target soluble domains or engineered constructs

• NMR spectroscopy:

  • Solution NMR applicable to smaller fragments or soluble domains

  • Solid-state NMR suitable for full-length protein in lipid environments

  • Can provide dynamic information not accessible by other methods

• Integrative approaches:

  • Combining low-resolution techniques with computational modeling

  • Cross-linking mass spectrometry to map interaction interfaces

  • Molecular dynamics simulations to probe dynamic behavior

The successful cryo-EM studies of mycobacterial ATP synthases demonstrate the feasibility of this approach for resolving structural details of large membrane protein complexes.

How can molecular dynamics simulations enhance our understanding of atpF function?

Molecular dynamics simulations offer unique insights into dynamic aspects:

• System preparation considerations:

  • Embedding in appropriate lipid bilayer composition

  • Inclusion of interacting subunits for context

  • Proper protonation states based on local pH

• Simulation types and applications:

  • Equilibrium simulations to assess conformational stability

  • Steered MD to investigate mechanical properties of the peripheral stalk

  • Coarse-grained simulations for longer timescales and larger systems

• Analysis approaches:

  • Principal component analysis to identify major motion modes

  • Hydrogen bond and salt bridge analysis

  • Residue interaction networks to identify communication pathways

These computational approaches can provide mechanistic insights into how the peripheral stalk, including atpF, mechanically couples the FO and F1 domains while resisting the torque generated during ATP synthesis.

What experimental designs can assess the impact of lipid environment on atpF structure and function?

The lipid environment critically influences membrane protein behavior:

• Systematic lipid screening:

  • Reconstitution in liposomes of varying composition

  • Assessment of protein stability and activity

  • Identification of specific lipid-protein interactions

• Native-like membrane mimetics:

  • Nanodiscs with controlled lipid composition

  • Bicelles for structural studies

  • Polymer-based systems (SMALP, DIBMA) for native extraction

• Lipid-protein interaction analysis:

  • Thin-layer chromatography of co-purifying lipids

  • Mass spectrometry to identify bound lipids

  • Molecular dynamics simulations to identify lipid binding sites

A systematic approach correlating lipid composition with functional parameters could reveal how P. vibrioformis atpF has adapted to function in its native membrane environment.

How can proteomics approaches be used to study the interactome of P. vibrioformis atpF?

Proteomics offers powerful tools for mapping protein interactions:

• Affinity purification-mass spectrometry:

  • Use tagged atpF as bait protein

  • Identify co-purifying proteins by mass spectrometry

  • Validate interactions through reciprocal pull-downs

• Proximity labeling approaches:

  • Fusion of atpF with BioID or APEX2

  • In vivo biotinylation of proximal proteins

  • Identification of labeled proteins by mass spectrometry

• Cross-linking mass spectrometry:

  • Chemical cross-linking of intact complexes

  • Identification of cross-linked peptides

  • Mapping of interaction interfaces at residue-level resolution

Similar approaches involving co-immunoprecipitation have been used to study subunit interactions in the Rnf complex , demonstrating their applicability to membrane protein complexes.

How does P. vibrioformis atpF compare to homologous subunits in other photosynthetic bacteria?

Comparative analysis can reveal adaptations specific to P. vibrioformis:

• Sequence-based comparisons:

  • Multiple sequence alignment to identify conserved and variable regions

  • Phylogenetic analysis to trace evolutionary relationships

  • Identification of lineage-specific insertions or deletions

• Structural comparisons:

  • Homology modeling based on known structures

  • Superposition to identify structural conservation and divergence

  • Analysis of surface properties and interaction interfaces

• Functional comparisons:

  • ATP synthesis efficiency under different conditions

  • Regulatory mechanisms controlling ATP hydrolysis

  • Stability in different environmental conditions

The specialized adaptations observed in coral-associated Prosthecochloris suggest that their ATP synthases, including atpF, might possess unique features compared to those from other photosynthetic bacteria.

What can be learned from comparing atpF between different Prosthecochloris strains adapted to diverse environments?

Intra-genus comparisons can reveal environment-specific adaptations:

The diverse habitats of Prosthecochloris species (hydrogen sulfide-rich mud, hot spring sediment, coral skeletons) provide natural experiments in adaptation that can inform our understanding of how atpF evolves to maintain function under different environmental constraints.

How have mobile genetic elements influenced the evolution of ATP synthase genes in Prosthecochloris?

Mobile genetic elements (MGEs) appear to play important roles in the evolutionary diversification of Prosthecochloris strains :

• Evidence assessment:

  • Identification of genomic islands near ATP synthase genes

  • Detection of insertion sequences or transposons

  • Analysis of GC content and codon usage as indicators of HGT

• Comparative genomic approaches:

  • Synteny analysis across Prosthecochloris genomes

  • Identification of atypical phylogenetic patterns

  • Detection of gene gain/loss events

• Functional implications:

  • Impact of MGE-mediated changes on protein function

  • Selection pressures maintaining acquired elements

  • Role in adaptation to specific environmental niches

The finding that MGEs or evidence of horizontal gene transfer were found in genomic loci associated with adaptive traits in coral-associated Prosthecochloris suggests similar mechanisms might influence the evolution of ATP synthase components like atpF.