Recombinant Anaeromyxobacter dehalogenans ATP synthase subunit b (atpF)

What is Anaeromyxobacter dehalogenans and why is its ATP synthase of interest to researchers?

Anaeromyxobacter dehalogenans is a unique bacterium that represents the first identified myxobacteria capable of anaerobic growth. It was isolated from soils and sediments based on its ability to use acetate as an electron donor and 2-chlorophenol as an electron acceptor . This organism exhibits distinctive physiological characteristics, including:

• Capability for facultative anaerobic growth using various electron acceptors including chlorophenols, nitrate, fumarate, and oxygen

• Reduction of nitrate to ammonium (respiratory ammonification)

• N₂O reduction to N₂ despite lacking typical denitrification genes (nirS/nirK)

• Ability to couple Fe(III) reduction with NO₃⁻/NO₂⁻ reduction through linked biotic-abiotic pathways

Its ATP synthase is of particular interest because it functions under diverse metabolic conditions, potentially with unique adaptations for energy conservation during anaerobic respiration. Understanding its subunit b (atpF), which forms part of the stator complex, provides insights into energy transduction mechanisms in metabolically versatile bacteria .

What is the structure and function of ATP synthase subunit b in bacteria?

ATP synthase subunit b (atpF) is a critical component of the F₁F₀ ATP synthase complex, which synthesizes ATP using the energy created by proton electrochemical gradients. Specifically:

• Subunit b forms part of the peripheral stalk (or "stator") of the F₁F₀ ATP synthase

• It connects the membrane-embedded F₀ portion to the catalytic F₁ portion

• It prevents rotation of the α₃β₃ hexamer relative to subunit a during catalysis

• The stator is crucial for stability of the c-ring/F₁ complex

In the ATP synthase complex, the stator and rotor components work together in a mechanical rotary mechanism. The stator components include α₃β₃, a, b, d, F₆, and OSCP, while the rotor consists of the c-ring, γ, δ, and ε subunits . The peripheral stalk formed partly by subunit b is essential for maintaining the structural integrity needed for efficient coupling between proton translocation and ATP synthesis.

What are the recommended expression systems for recombinant A. dehalogenans ATP synthase subunit b?

Based on current research practices with ATP synthase subunits and available recombinant protein production systems, researchers have several options:

What purification challenges are specific to recombinant ATP synthase subunit b from A. dehalogenans?

Purification of recombinant ATP synthase subunit b presents several challenges:

• Hydrophobicity: As part of the peripheral stalk, subunit b contains hydrophobic regions that interact with the membrane, potentially causing aggregation during purification.

• Stability concerns: The isolated subunit may be less stable than when assembled in the complete complex, requiring optimization of buffer conditions.

• Recommended purification strategy:

  • Initial capture using immobilized metal affinity chromatography (IMAC) with a His-tag

  • Intermediate purification with ion exchange chromatography

  • Final polishing with size exclusion chromatography

• Buffer optimization: Buffer systems containing 50 mM Tris-HCl (pH 8.0), 100-300 mM NaCl, and 5% glycerol have proven effective for maintaining stability of isolated ATP synthase subunits .

For functional studies, detergent selection is critical. Mild detergents like n-dodecyl β-D-maltoside (DDM) at 0.05-0.1% are often suitable for membrane protein components while preserving native-like structure.

How does the structure of A. dehalogenans ATP synthase subunit b differ from other bacterial homologs?

Comparative analysis of ATP synthase subunit b across bacterial species reveals both conserved features and distinct characteristics in A. dehalogenans:

• Conserved features: Maintains the core structural elements required for peripheral stalk formation and interaction with other ATP synthase subunits

• Unique aspects of A. dehalogenans atpF:

  • Adaptation to function under both aerobic and anaerobic conditions

  • Potential specialized interactions with other subunits that may reflect the organism's metabolic versatility

  • Possible modifications that facilitate energy conservation during diverse respiratory processes

While detailed structural analysis specific to A. dehalogenans ATP synthase is still emerging, research on other bacterial ATP synthases indicates that variations in subunit b can influence the efficiency of energy coupling and the stability of the enzyme complex under different environmental conditions .

What experimental approaches are recommended for investigating the coupling function of ATP synthase subunit b in A. dehalogenans?

To investigate the coupling function of ATP synthase subunit b, researchers should consider these methodological approaches:

• Site-directed mutagenesis studies:

  • Creating mutations in conserved residues similar to the approach used in the mycobacterial ε subunit study (εR105A,R111A,R113A,R115A)

  • Measuring effects on ATP synthesis, growth rates, and respiratory parameters

• Reconstitution experiments:

  • Incorporating purified recombinant subunit b into liposomes along with other ATP synthase components

  • Measuring proton translocation and ATP synthesis rates in the reconstituted system

• Cross-linking studies:

  • Using chemical cross-linking coupled with mass spectrometry to map interactions between subunit b and other components of the ATP synthase complex

  • Identifying critical residues involved in complex stability

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

  • Mapping flexible regions and protein-protein interaction interfaces, similar to approaches used for other bacterial proteins

  • Identifying conformational changes under different conditions (aerobic vs. anaerobic)

These approaches can provide insights into how subunit b contributes to the coupling efficiency of ATP synthesis in A. dehalogenans, particularly under the diverse respiratory conditions this organism experiences.

How does the ATP synthase in A. dehalogenans contribute to its metabolic versatility under different respiratory conditions?

A. dehalogenans exhibits remarkable metabolic versatility, and its ATP synthase plays a central role in energy conservation across diverse respiratory conditions:

• During anaerobic respiration with chlorophenols:

  • ATP synthase harnesses the proton gradient generated through chlororespiration

  • The F₁F₀ complex must maintain efficient coupling despite lower energy yield compared to aerobic respiration

• During nitrate respiration:

  • A. dehalogenans reduces nitrate to ammonium through respiratory ammonification

  • ATP synthase adapts to utilize the proton gradient established through this process

  • When Fe(II) is present, A. dehalogenans can reduce NO₃⁻ to N₂ through linked biotic-abiotic reactions

• During microaerophilic growth:

  • A. dehalogenans exhibits oxygen-dependent growth with decreasing growth rates at higher oxygen levels

  • The fraction of electrons used for biomass production (fs) decreases from 0.52 at pO₂ of 0.02 atm to 0.19 at higher pO₂ levels

  • ATP synthase likely undergoes regulation to optimize energy conservation under varying oxygen levels

The atpF subunit contributes to maintaining structural integrity of the ATP synthase complex under these diverse conditions, ensuring efficient energy transduction despite changing environmental parameters .

What methodological approaches can detect alterations in coupling efficiency when studying modified forms of ATP synthase subunit b?

Researchers can employ several complementary techniques to assess coupling efficiency changes in modified ATP synthase subunit b:

• Membrane vesicle assays:

  • Preparation of inverted membrane vesicles containing wild-type or modified ATP synthase

  • Measurement of ATP synthesis driven by artificially imposed proton gradients

  • Comparison of ATP synthesis rates between wild-type and modified systems

• Respiration measurements:

  • Oxygen consumption rates using oxygen electrodes

  • Measurement of respiratory control ratios (state 3/state 4 respiration)

  • Assessment of P/O ratios (ATP produced per oxygen consumed)

• Membrane potential measurements:

  • Using fluorescent probes (e.g., DiSC3(5), TMRM) to monitor membrane potential

  • Correlation between membrane potential and ATP synthesis rates

• Direct ATP measurements:

  • Bioluminescence assays measuring ATP levels under different conditions

  • Comparison of ATP/ADP ratios between wild-type and modified systems

• Growth yield determination:

  • Measurement of molar growth yields on different carbon sources

  • Calculation of ATP produced per substrate consumed

  • Comparison between systems with wild-type and modified subunit b

These approaches provide quantitative insights into how modifications to subunit b affect the coupling efficiency of ATP synthesis, which is particularly relevant when studying ATP synthase from metabolically versatile organisms like A. dehalogenans.

How might the unique properties of A. dehalogenans ATP synthase be exploited for bioremediation applications?

A. dehalogenans has significant potential for bioremediation applications, with its ATP synthase playing a key role in energetic efficiency during such processes:

• Chlorinated compound remediation:

  • A. dehalogenans can use chlorophenols as electron acceptors for growth

  • ATP synthase efficiency determines growth rates and bioremediation capacity

  • Understanding subunit b function could help optimize energy conservation during chlororespiration

• Nitrous oxide reduction in agricultural soils:

  • A. dehalogenans belongs to nondenitrifiers with atypical nosZ genes that reduce N₂O to N₂

  • The abundance of Anaeromyxobacter cells in agricultural soils ranges from 10⁵ to 10⁷ cells per gram, similar to complete denitrifiers

  • Energy conservation through ATP synthase supports growth during N₂O reduction

• Post-oxygen intrusion resilience:

  • A. dehalogenans shows increased cell numbers after oxygen intrusion in uranium-contaminated sites

  • Unlike other anaerobes, A. dehalogenans can grow under microaerophilic conditions, providing an advantage in fluctuating redox environments

  • ATP synthase adaptability to different electron acceptors enables this resilience

Research focused on optimizing ATP synthase function through directed evolution or synthetic biology approaches could enhance A. dehalogenans' bioremediation capabilities in contaminated environments.

What are the implications of studying ATP synthase coupling mechanisms in A. dehalogenans for developing new antimicrobial strategies?

Understanding the coupling mechanisms of A. dehalogenans ATP synthase has significant implications for antimicrobial development:

• Novel target identification:

  • Unique structural features of A. dehalogenans ATP synthase subunits could represent selective targets

  • Similar to mycobacterial F-ATP synthase, where disrupting coupling within subunit ε affects growth and cell wall biosynthesis

• Inhibitor development strategies:

  • In silico screening approaches similar to those used for mycobacterial F-ATP synthase inhibitors

  • Structure-based design targeting the unique interfaces between ATP synthase subunits

  • Focus on disrupting coupling rather than catalytic activity may provide selectivity

• Resistance considerations:

  • Understanding the evolutionary conservation of coupling mechanisms across bacterial species

  • Identifying targets with low mutation potential to minimize resistance development

  • Comparative analysis with human ATP synthase to ensure selectivity

• Potential antimicrobial applications:

  • Against A. dehalogenans itself in scenarios where its activity is undesirable

  • Against related bacteria with similar ATP synthase architecture

  • As adjuvants to existing antimicrobials by compromising bacterial energy metabolism

Research in this area could lead to novel antimicrobial strategies that target energy conservation mechanisms in bacteria, potentially addressing the growing challenge of antimicrobial resistance.

How do post-translational modifications affect the function of ATP synthase subunit b in A. dehalogenans under different environmental conditions?

Post-translational modifications (PTMs) likely play significant roles in regulating ATP synthase function in A. dehalogenans, particularly when adapting to changing environmental conditions:

• Potential phosphorylation sites:

  • Similar to phosphorylation of the β subunit in other ATP synthases, which can have distinct effects on complex structure and function

  • Phosphorylation may alter the interactions between subunit b and other components of the stator

• Environmental triggers for PTMs:

  • Transition between aerobic and anaerobic conditions

  • Changes in substrate availability

  • Exposure to environmental stressors

• Functional consequences:

  • Modification of coupling efficiency

  • Alteration of complex stability

  • Regulation of ATP synthase assembly or disassembly

• Methodological approaches to study PTMs:

  • Phosphoproteomics to identify modification sites

  • Site-directed mutagenesis of potential modification sites to generate non-modifiable or phosphomimetic variants

  • Functional assays to assess the impact of modifications on ATP synthesis activity

Understanding how PTMs regulate ATP synthase function in A. dehalogenans could provide insights into adaptation mechanisms employed by this metabolically versatile bacterium when facing changing environmental conditions .

What are the most pressing research questions regarding A. dehalogenans ATP synthase that remain to be addressed?

Several critical research questions regarding A. dehalogenans ATP synthase merit further investigation:

• Structural adaptations:

  • How does the structure of A. dehalogenans ATP synthase differ from other bacterial ATP synthases?

  • What structural features enable it to function efficiently under diverse respiratory conditions?

• Regulatory mechanisms:

  • How is ATP synthase activity regulated during transitions between different electron acceptors?

  • What signaling pathways coordinate ATP synthase function with respiratory chain components?

• Evolution and horizontal gene transfer:

  • Has A. dehalogenans acquired unique ATP synthase features through horizontal gene transfer?

  • How has the ATP synthase complex evolved to support the organism's diverse metabolic capabilities?

• Bioenergetic efficiency:

  • How does the ATP yield per substrate differ when using different electron acceptors?

  • What mechanisms optimize energy conservation during less energetically favorable processes?

These research questions will require interdisciplinary approaches combining structural biology, biochemistry, molecular biology, and systems biology to fully understand the unique characteristics of A. dehalogenans ATP synthase.

What novel experimental techniques might advance our understanding of ATP synthase function in A. dehalogenans?

Emerging techniques that could significantly advance research on A. dehalogenans ATP synthase include:

• Cryo-electron microscopy (cryo-EM):

  • Determination of high-resolution structures of the complete ATP synthase complex

  • Visualization of conformational changes under different conditions

• Single-molecule techniques:

  • Direct observation of ATP synthase rotary motion using fluorescent probes

  • Measurement of torque generation and energy transduction efficiency at the single-molecule level

• In situ structural studies:

  • Cryo-electron tomography of ATP synthase in native membranes

  • Correlative light and electron microscopy to study ATP synthase distribution and dynamics

• Advanced genetic tools:

  • Development of genetic systems specifically for A. dehalogenans

  • CRISPR-Cas9 based genome editing to create precise mutations in ATP synthase genes

• Computational approaches:

  • Molecular dynamics simulations of the complete ATP synthase complex

  • In silico prediction of subunit interactions and energy transduction mechanisms

These advanced techniques will provide unprecedented insights into the structure, function, and regulation of ATP synthase in A. dehalogenans, contributing to our understanding of energy conservation in this metabolically versatile bacterium.