Recombinant Desulfotomaculum reducens ATP synthase subunit b (atpF)

What is the role of ATP synthase subunit b in Desulfotomaculum reducens?

ATP synthase subunit b (atpF) in D. reducens is a membrane-bound component of the F₀ portion of ATP synthase that forms the peripheral stalk connecting the F₁ catalytic domain to the membrane-embedded F₀ domain. This connection is crucial for coupling proton translocation to ATP synthesis during oxidative phosphorylation. In D. reducens, ATP synthase likely plays a significant role in energy conservation during both respiratory and fermentative growth conditions .

What growth conditions affect the expression of atpF in D. reducens?

Based on transcriptomic studies of D. reducens, proteins involved in respiration show differential expression under various growth conditions. For instance, respiratory proteins like NADH quinone oxidoreductase are up-regulated during fermentative growth in the presence of U(VI) . While specific data on atpF expression is not directly provided, ATP synthase components would likely be more highly expressed during respiratory growth compared to fermentative conditions, as observed with other energy metabolism proteins in this organism .

What expression systems are most effective for recombinant D. reducens atpF protein?

For expression of recombinant proteins from D. reducens, E. coli expression systems using vectors with inducible promoters (like T7) are commonly employed. Based on protocols used for other ATP synthase components, the following approach could be effective:

• Clone the atpF gene into an expression vector with a His-tag for purification

• Transform into an E. coli expression strain (e.g., BL21(DE3))

• Grow cells aerobically at 37°C in terrific broth medium with appropriate antibiotics

• Induce expression with IPTG at optimal cell density

• Harvest cells and purify using affinity chromatography

What purification strategy yields the highest purity for recombinant atpF?

A multi-step purification approach is recommended:

• Initial capture using Ni²⁺-NTA affinity chromatography:

  • Equilibrate column with 20 mM imidazole and 100 mM NaCl, pH 7.0

  • Apply cell lysate containing His-tagged atpF protein

  • Wash with 50 mM imidazole and 100 mM NaCl, pH 7.0

  • Elute with 500 mM imidazole and 100 mM NaCl, pH 7.0

• Secondary purification via ion exchange chromatography

• Final polishing step using size exclusion chromatography

• Storage as precipitate in 70% saturated ammonium sulfate at 4°C for maximum stability

How can researchers assess the proper folding of recombinant atpF?

To assess proper folding of recombinant atpF, researchers should employ multiple complementary techniques:

• Circular Dichroism (CD) spectroscopy to assess secondary structure

• Intrinsic fluorescence spectroscopy to evaluate tertiary structure

• Limited proteolysis followed by mass spectrometry to identify protected regions

• Thermal shift assays to determine protein stability

• Functional reconstitution assays to verify biological activity

Properly folded atpF would likely interact with other ATP synthase components, particularly the α and β subunits, which could be verified through pull-down assays or surface plasmon resonance .

What experimental approaches can determine if recombinant atpF integrates properly into ATP synthase complexes?

Researchers can employ several methods to assess proper integration:

• Reconstitution experiments: Incorporate purified recombinant atpF into liposomes or nanodiscs along with other ATP synthase components.

• Functional coupling assays: Measure ATP synthesis or hydrolysis activities in reconstituted systems.

• FRET analysis: Label recombinant atpF and other subunits with fluorophore pairs to detect proper assembly through energy transfer.

• Crosslinking studies: Use chemical crosslinkers to identify protein-protein interactions between atpF and other ATP synthase components.

• Electron microscopy: Visualize the assembled complex to confirm structural integrity .

How does atpF contribute to the unique energy metabolism of D. reducens?

D. reducens has versatile energy metabolism pathways, including sulfate reduction, Fe(III) reduction, and fermentation. The ATP synthase, including its subunit b (atpF), likely plays different roles depending on growth conditions:

• During respiratory growth (sulfate or Fe(III) reduction), ATP synthase functions in its canonical role, using the proton gradient generated by electron transport for ATP synthesis.

• During Fe(III) reduction with lactate, where little energy is conserved, ATP synthase might operate with reduced efficiency.

• Under fermentative conditions, ATP synthase components might be down-regulated as substrate-level phosphorylation becomes the primary ATP generation method .

The unique adaptations of atpF might contribute to D. reducens' ability to thrive in anaerobic environments with various electron acceptors.

What methods can determine the coupling efficiency of ATP synthase containing recombinant atpF?

Researchers can assess coupling efficiency using these approaches:

• H⁺-pumping assays: Measure ATP-driven proton pumping using pH-sensitive fluorescent dyes (like ACMA) in reconstituted systems.

• ATP synthesis assays: Determine the ATP synthesis rate in response to artificially imposed proton gradients.

• ATP hydrolysis assays: Measure ATPase activity under various conditions.

• Temperature dependence studies: Analyze how temperature affects the coupling between ATP hydrolysis and proton translocation.

• Proton/ATP ratio determination: Calculate the number of protons required for the synthesis of one ATP molecule.

Note: The table contains framework values as specific experimental data for D. reducens atpF is not available in the provided search results .

How do mutations in the transmembrane domain of atpF affect proton translocation?

Mutations in the transmembrane domain of atpF could significantly impact proton translocation through the F₀ complex. Research approaches to investigate this include:

• Site-directed mutagenesis: Create point mutations in conserved residues of the transmembrane domain.

• Growth analysis: Determine if mutant strains can grow under conditions requiring ATP synthase function.

• Proton pumping assays: Measure the ability of mutant ATP synthases to establish proton gradients.

• ATP synthesis/hydrolysis coupling: Quantify the efficiency of energy conversion in mutant enzymes.

• Structural studies: Use techniques like cryo-EM to detect structural changes caused by mutations.

These approaches would help understand how specific residues in atpF contribute to the proton translocation mechanism, similar to studies done on the β subunit loop of ATP synthase .

What is the role of atpF in the adaptation of D. reducens to various electron acceptors?

D. reducens can use various electron acceptors including sulfate and Fe(III). The ATP synthase, including atpF, might adapt to these different growth conditions:

• During sulfate reduction, a complete electron transport chain likely generates a strong proton motive force, making ATP synthase highly active.

• During Fe(III) reduction with lactate, where direct contact with the electron acceptor is required, energy conservation is limited, potentially affecting ATP synthase operation .

• The expression and perhaps post-translational modifications of atpF might vary under different electron-accepting conditions.

Research approaches could include:

• Comparative transcriptomics and proteomics under different growth conditions

• In vivo cross-linking studies to identify interaction partners specific to different metabolic states

• Mutational analysis to identify regions of atpF important for function with specific electron acceptors

What are the major challenges in expressing and reconstituting functional recombinant atpF?

Researchers face several challenges when working with recombinant atpF:

• Membrane protein expression: As a component normally embedded in the membrane, atpF may form inclusion bodies when overexpressed.

• Proper folding: Ensuring correct folding in the absence of the complete ATP synthase complex.

• Protein stability: Maintaining stability during purification and reconstitution experiments.

• Functional reconstitution: Assembling atpF with other ATP synthase components in the correct stoichiometry and orientation.

• Anaerobic conditions: D. reducens is an anaerobe, so its proteins may have special requirements for expression and handling.

Strategies to address these challenges include using specialized expression hosts, fusion tags to improve solubility, detergent screening for optimal extraction, and careful optimization of reconstitution conditions .

How can researchers distinguish between direct and indirect effects of atpF mutations?

Distinguishing direct from indirect effects of atpF mutations requires a multi-faceted approach:

• Comprehensive phenotypic analysis: Compare growth rates, ATP production, and membrane potential across different growth conditions.

• Complementation studies: Reintroduce wild-type or mutant atpF to confirm the phenotype is directly related to the mutation.

• Biochemical characterization: Purify the mutant ATP synthase complex and assess its properties in vitro.

• Structure-function analysis: Correlate observed phenotypes with structural changes using techniques like FRET to measure distances between components.

• In vivo crosslinking: Identify altered protein-protein interactions caused by mutations.

This systematic approach helps separate direct effects on ATP synthase function from broader metabolic adaptations .

How does the ATP synthase complex interact with the dissimilatory sulfate reduction pathway in D. reducens?

In D. reducens, ATP synthase likely has important functional connections with the dissimilatory sulfate reduction (DSR) pathway:

• Energy coupling: The electron transport chain associated with sulfate reduction generates a proton motive force utilized by ATP synthase.

• Regulatory interactions: Expression of ATP synthase genes may be co-regulated with DSR genes like those encoding the dissimilatory sulfite reductase (DsrAB).

• Metabolic balancing: ATP generated by ATP synthase is consumed in the activation of sulfate to APS (adenosine 5'-phosphosulfate) by ATP sulfurylase, creating a metabolic cycle.

• Protein-protein interactions: While not directly demonstrated, ATP synthase components might physically associate with respiratory complexes involved in the electron transport chain supporting sulfate reduction .

The DsrD protein, which acts as an allosteric activator in the sulfite reduction pathway, is expressed under respiratory but not fermentative conditions, suggesting coordinated regulation with energy conservation systems like ATP synthase .

What role does atpF play in the response of D. reducens to uranium exposure?

Transcriptomic studies have shown that D. reducens upregulates respiratory proteins during uranium exposure under fermentative conditions. While atpF specifically wasn't mentioned in the available search results, ATP synthase likely plays a role in this response:

• Energy conservation: The upregulation of respiratory proteins (NADH quinone oxidoreductase, heterodisulfide reductase) suggests electrons may be shuttled to the electron transport chain during U(VI) exposure, potentially involving ATP synthase in energy conservation.

• Stress response: Uranium exposure may increase energy demands for cellular detoxification and repair mechanisms, requiring efficient ATP synthesis.

• Redox balancing: ATP synthase might help maintain cellular redox balance during uranium reduction.

Further research specifically examining atpF expression and ATP synthase activity during uranium exposure would help clarify these relationships .

What novel experimental techniques could advance our understanding of atpF function?

Several cutting-edge approaches could advance research on D. reducens atpF:

• Cryo-electron microscopy: Determine high-resolution structures of the complete ATP synthase complex from D. reducens under different metabolic conditions.

• Single-molecule FRET: Visualize conformational changes in atpF during the catalytic cycle.

• In-cell NMR: Study the dynamics and interactions of atpF in living cells.

• Proteomics with crosslinking-mass spectrometry: Map the protein interaction network of atpF within the ATP synthase complex and potentially with other cellular components.

• CRISPR-based approaches: Create targeted mutations to study atpF function in vivo with minimal disruption to other cellular processes.

• Microfluidics-based assays: Develop high-throughput systems to study ATP synthase function under precisely controlled conditions .

How might studying atpF contribute to understanding the evolution of energy conservation in anaerobic bacteria?

Studying atpF from D. reducens could provide valuable insights into the evolution of energy conservation mechanisms:

• Comparative genomics: Analysis of atpF sequences across sulfate-reducing and metal-reducing bacteria could reveal evolutionary adaptations to different energy landscapes.

• Structural comparisons: Identifying unique features of D. reducens atpF compared to aerobic bacteria might reveal adaptations specific to anaerobic energy conservation.

• Functional analysis of conserved motifs: Determining which regions of atpF are highly conserved could highlight critical functional domains across bacterial lineages.

• Ancestral sequence reconstruction: Recreating and characterizing predicted ancestral versions of atpF could provide insights into the evolution of ATP synthase function.

• Analysis of horizontal gene transfer events: Identifying potential instances where atpF or ATP synthase components might have been transferred between distantly related anaerobes.

This research could help piece together how energy conservation mechanisms evolved in diverse anaerobic lifestyles, particularly in conjunction with studies on other energy-related proteins like the DsrD protein, which appears later in evolution relative to DsrAB in the dissimilatory sulfur metabolism pathway .