Recombinant Desulfococcus oleovorans ATP synthase subunit b 1 (atpF1)

What is Desulfococcus oleovorans and why is its ATP synthase of research interest?

Desulfococcus oleovorans strain Hxd3 is a delta-proteobacterium isolated from a northern German oil field. It is scientifically significant as the only known pure culture capable of carboxylating aliphatic hydrocarbons, utilizing C12-C20 alkanes as growth substrates through a unique metabolic pathway . Its ATP synthase, particularly the b subunits, represents an interesting research model for understanding energy metabolism in anaerobic sulfate-reducing bacteria that thrive in hydrocarbon-rich environments.

The ATP synthase from this organism may contain adaptations that enable energy production under the unusual growth conditions required by this bacterium. Research on its atpF1 gene product (subunit b 1) contributes to our understanding of how energy production mechanisms have evolved in specialized environmental niches.

How does D. oleovorans ATP synthase compare to other bacterial ATP synthases?

D. oleovorans ATP synthase shares the fundamental F1FO architecture found in other bacterial ATP synthases but displays certain distinguishing characteristics :

Unlike some specialized ATP synthases (such as from Aquifex aeolicus), the D. oleovorans enzyme does not appear to be Na+-dependent, based on comparative sequence analysis with other characterized ATP synthases .

What expression systems have been successfully used for recombinant production of D. oleovorans ATP synthase subunit b 1?

Several expression systems have been successfully used for producing recombinant D. oleovorans ATP synthase subunit b 1, each with advantages for different research applications :

For functional studies of the entire ATP synthase complex, E. coli has been the predominant system, particularly when co-expressing multiple subunits. Expression vectors typically incorporate T7 promoters and appropriate ribosome binding sites to enhance protein production .

How can I optimize soluble expression of recombinant D. oleovorans ATP synthase subunit b 1 in E. coli?

Optimizing soluble expression of D. oleovorans ATP synthase subunit b 1 in E. coli requires addressing several key challenges inherent to membrane protein expression :

• Codon optimization strategy:

  • Analyze codon usage differences between D. oleovorans and E. coli

  • Optimize rare codons, particularly for the membrane-spanning domains

  • Eliminate problematic secondary structures in mRNA

• Fusion partner selection:

  • MBP (maltose binding protein) fusion increases solubility significantly

  • The MBP-atpF1 fusion approach has been successful for other ATP synthase subunits

• Expression parameters optimization:

  • Lower induction temperature (16-20°C)

  • Reduced IPTG concentration (0.1-0.5 mM)

  • Extended expression time (18-24 hours)

  • Rich media supplemented with glucose

• Membrane protein-specific considerations:

  • Addition of membrane-mimicking detergents post-lysis

  • Co-expression with chaperones (GroEL/GroES, DnaK)

  • Use of C41(DE3) or C43(DE3) E. coli strains specifically developed for membrane protein expression

Based on successful strategies with similar proteins, using pET-based vectors with a cleavable N-terminal tag (His6-MBP) provides the best balance of expression and downstream purification options .

What is the recommended protocol for co-expression of ATP synthase subunits b1 and b2 in E. coli?

For functional studies of the ATP synthase, co-expression of subunits b1 and b2 is crucial. The recommended protocol based on successful expression of other ATP synthase components is :

• Vector construction:

  • Clone atpF1 (b1) and atpF2 (b2) genes into a dual-expression vector

  • Alternatively, use a synthetic operon approach with genes in their natural order

  • Include ribosome binding sites upstream of each gene

  • Example construct: atpF1-RBS-atpF2 in pCL02 vector

• Transformation and culture:

  • Transform into C43(DE3) E. coli strain

  • Grow cells at 37°C to OD600 of 0.6-0.8

  • Induce with 0.5 mM IPTG

  • Shift temperature to 20°C

  • Continue expression for 18 hours

• Verification of co-expression:

  • Prepare membrane fractions by ultracentrifugation

  • Analyze by SDS-PAGE with heat treatment at 95°C for 5 minutes

  • Confirm expression by western blot using antibodies specific to each subunit

  • Verify complex formation by Blue-Native PAGE and mass spectrometry

This approach has been shown to yield stable b1-b2 subcomplexes that can be isolated from E. coli membranes with detergents like DDM or Triton X-100 .

What is the optimal purification strategy for recombinant D. oleovorans ATP synthase subunit b 1?

The optimal purification strategy for recombinant D. oleovorans ATP synthase subunit b 1 combines several techniques to achieve high purity while maintaining protein structure and function :

• Membrane fraction preparation:

  • Cell disruption by French press or sonication

  • Low-speed centrifugation to remove cell debris (10,000 × g, 20 min)

  • Ultracentrifugation to collect membranes (150,000 × g, 1 hour)

  • Membrane washing with high-salt buffer (300 mM NaCl)

• Solubilization:

  • Solubilize membranes in 1% DDM or other mild detergent

  • Include 20 mM imidazole to reduce non-specific binding

  • Incubate with gentle rotation for 1 hour at 4°C

  • Clarify by ultracentrifugation (150,000 × g, 30 min)

• Affinity chromatography:

  • Apply solubilized protein to Ni-NTA column

  • Wash with 20-50 mM imidazole

  • Elute with 250-300 mM imidazole

  • Concentrate using a 30 kDa MWCO concentrator

• Size exclusion chromatography:

  • Apply concentrated protein to Superdex 200 column

  • Use buffer containing 0.05% DDM to maintain solubility

  • Collect fractions corresponding to monomeric or dimeric species

  • Analyze by SDS-PAGE and western blotting

For highest purity, incorporate an ion exchange chromatography step between the affinity and size exclusion steps.

How can the structural integrity of purified D. oleovorans ATP synthase subunit b 1 be assessed?

Assessing the structural integrity of purified D. oleovorans ATP synthase subunit b 1 is critical for functional studies. Several complementary approaches are recommended :

• Circular dichroism (CD) spectroscopy:

  • Measures secondary structure content (α-helical, β-sheet)

  • Typical spectrum should show high α-helical content (minima at 208 and 222 nm)

  • Thermal stability can be assessed by recording spectra at increasing temperatures

• Mass spectrometry approaches:

  • Intact mass analysis to confirm correct primary sequence

  • Peptide mass fingerprinting (PMF) after tryptic digestion

  • Native MS to assess oligomeric state

• Limited proteolysis:

  • Correctly folded protein shows resistance to proteolytic digestion

  • Compare proteolytic patterns of purified protein to predicted fragments

  • Analyze by SDS-PAGE or mass spectrometry

• Blue-Native PAGE:

  • Assess formation of higher-order complexes or subunit interactions

  • Silver staining following electrophoresis

  • Compare to known molecular weight standards

Proper structural integrity is indicated by a predominantly α-helical CD spectrum, correct molecular weight by MS, and discrete bands on Blue-Native PAGE corresponding to monomeric or dimeric species.

What methods can be used to characterize the interaction between subunit b 1 and other ATP synthase components?

Characterizing interactions between ATP synthase subunit b 1 and other components requires specialized techniques for membrane protein complexes :

These approaches provide complementary information about the interaction network within the ATP synthase complex, particularly the critical interactions between the b subunits and the F1 sector.

How can I assess the functionality of recombinantly expressed D. oleovorans ATP synthase subunits?

Functional assessment of recombinant D. oleovorans ATP synthase subunits involves several complementary approaches :

• ATP hydrolysis activity assay:

  • Measure inorganic phosphate release using colorimetric methods (malachite green assay)

  • Monitor ATP hydrolysis with an enzyme-coupled assay (NADH oxidation)

  • In-gel ATP hydrolysis activity using non-denaturing PAGE and lead phosphate precipitation

• Reconstitution into liposomes:

  • Incorporate purified ATP synthase or subcomplexes into liposomes

  • Create proton gradient using acid-base transition or valinomycin/K+

  • Measure ATP synthesis upon energization

  • Use luciferin/luciferase system for real-time ATP detection

• Membrane potential measurements:

  • Use fluorescent probes (ACMA, Oxonol VI) to monitor membrane potential

  • Measure proton translocation coupled to ATP hydrolysis

  • Assess ion specificity using different ions in the buffer

• Inhibitor studies:

  • Test sensitivity to known ATP synthase inhibitors

  • DCCD specifically modifies the essential carboxyl group in subunit c

  • Oligomycin inhibits the FO sector

  • Determine IC50 values and compare to well-characterized ATP synthases

For example, functional ATP synthases typically show ATP hydrolysis rates of 0.5-5 μmol min^-1 mg^-1, with DCCD inhibition of >90% at 100 μM concentration .

What role does the b 1 subunit play in the assembly and function of the complete ATP synthase complex?

The b 1 subunit plays critical roles in ATP synthase assembly and function, which can be experimentally investigated :

• Structural role:

  • Forms part of the peripheral stalk (with b 2 subunit)

  • Connects membrane-embedded FO sector to catalytic F1 sector

  • Provides structural stability to the entire complex

  • Counteracts torque generated during catalysis

• Assembly role:

  • Acts as a scaffold for assembly of other subunits

  • Facilitates correct positioning of the F1 sector

  • Coordinates c-ring formation with other FO components

• Functional role:

  • Participates in energy transfer during catalysis

  • Contributes to elasticity needed for rotary mechanism

  • Maintains proper spacing between FO and F1 sectors

• Experimental approaches to study these roles:

  • Deletion mutants to assess assembly defects

  • Site-directed mutagenesis of key residues

  • Cross-linking studies to identify interaction partners

  • Fusion constructs to probe spatial requirements

How does the ion specificity of D. oleovorans ATP synthase compare to other bacterial ATP synthases?

The ion specificity of D. oleovorans ATP synthase can be analyzed through comparative functional studies :

• Evidence for H+-dependency:

  • Sequence analysis shows conserved carboxyl residues in subunit c

  • DCCD labeling of the essential carboxyl group in subunit c

  • Lack of Na+-binding motifs found in Na+-dependent ATP synthases

• Experimental approaches to determine ion specificity:

  • ATP synthesis/hydrolysis assays in buffers with varying Na+/H+ concentrations

  • pH dependence of enzyme activity

  • Effect of specific inhibitors (EIPA for Na+/H+ exchangers)

  • Isotope exchange experiments with 22Na+ or tritiated water

• Comparative analysis:

  • Unlike Aquifex aeolicus, which shows Na+-dependent ATP synthesis

  • Similar to E. coli F1FO ATP synthase (H+-dependent)

  • Distinct from V-type ATPases in ion translocation mechanism

• Structural basis for ion specificity:

  • Key residues in subunits a and c determine ion specificity

  • Specific distance between essential residues in the ion channel

  • Binding pocket characteristics in the rotor-stator interface

Sequence analysis of D. oleovorans subunit c shows closer similarity to H+-dependent ATP synthases than to Na+-dependent enzymes, suggesting a proton-dependent mechanism despite its adaptation to high-salt environments .

How can recombinant D. oleovorans ATP synthase components be used to study the evolution of energy-coupling mechanisms?

Recombinant D. oleovorans ATP synthase components offer valuable tools for evolutionary studies of energy-coupling mechanisms :

• Hybrid ATP synthases construction:

  • Replace subunits between different species' ATP synthases

  • Create chimeric proteins with domains from multiple species

  • Test functionality of hybrid complexes

• Sequence-structure-function relationships:

  • Identify conserved motifs across diverse species

  • Correlate sequence variations with functional adaptations

  • Map evolutionary conservation onto structural models

• Adaptation to specific environments:

  • Compare ATP synthases from organisms in different ecological niches

  • Identify specific adaptations to high salt or hydrocarbon environments

  • Reconstruct ancestral sequences to test evolutionary hypotheses

• Research design approach:

  • Construct phylogenetic trees of ATP synthase subunits

  • Identify key residue changes during evolution

  • Use site-directed mutagenesis to revert/introduce evolutionary changes

  • Test functional consequences using reconstituted systems

As an anaerobic, sulfate-reducing bacterium from an oil field environment, D. oleovorans may possess unique adaptations in its ATP synthase that provide insights into the evolution of energy metabolism under extreme conditions .

What technical challenges must be overcome when studying membrane proteins like ATP synthase subunits from D. oleovorans?

Studying membrane proteins like ATP synthase subunits presents several technical challenges that require specialized approaches :

• Expression challenges:

  • Toxicity to host cells during overexpression

  • Inclusion body formation

  • Proper membrane insertion

  • Solution: Use specialized expression strains, fusion partners, and controlled induction

• Solubilization difficulties:

  • Finding optimal detergents for extraction

  • Maintaining native structure during solubilization

  • Preventing aggregation

  • Solution: Screen detergent panels, use mild solubilization conditions, add stabilizing agents

• Purification complications:

  • Detergent micelle contribution to apparent size

  • Co-purification of lipids and other membrane proteins

  • Detergent exchange during chromatography

  • Solution: Use specialized purification strategies for membrane proteins, incorporate detergent exchange steps

• Structural analysis limitations:

  • Challenges in crystallization for X-ray crystallography

  • Size limitations for NMR studies

  • Detergent background in mass spectrometry

  • Solution: Use complementary approaches (cryo-EM, HDX-MS, cross-linking)

• Functional reconstitution hurdles:

  • Maintaining proper orientation in liposomes

  • Controlling protein:lipid ratio

  • Ensuring proton/ion tightness

  • Solution: Optimize proteoliposome preparation, use fluorescent assays to verify orientation

Addressing these challenges requires specialized equipment, extensive optimization, and often the development of novel methodological approaches .

How might the study of D. oleovorans ATP synthase inform the development of novel antimicrobial strategies?

The study of D. oleovorans ATP synthase has significant implications for antimicrobial development, particularly against related pathogenic bacteria :

• Structural basis for selective targeting:

  • Identification of unique features not present in human ATP synthases

  • Comparison with mycobacterial ATP synthases already targeted by drugs

  • Structure-based drug design targeting bacterial-specific elements

• Lessons from existing ATP synthase inhibitors:

  • Bedaquiline (TMC207) targets mycobacterial ATP synthase

  • Understanding species selectivity mechanisms

  • Identification of conserved drug-binding pockets

• Potential target sites in ATP synthase:

  • Interface between subunits a and c

  • Species-specific regulatory elements (e.g., C-terminal domains)

  • Peripheral stalk components (b subunits)

  • Unique coupling elements between FO and F1 sectors

• Experimental approaches for inhibitor development:

  • High-throughput screening against reconstituted ATP synthase

  • Fragment-based drug discovery targeting specific subunits

  • Structure-guided modification of known inhibitors

  • Phenotypic screening followed by target validation

• Potential advantages of ATP synthase as a drug target:

  • Essential for energy metabolism

  • Surface-exposed portions accessible to drugs

  • Highly conserved in bacteria but distinct from human counterparts

  • Multiple potential binding sites for different inhibitor classes

While D. oleovorans itself is not pathogenic, the insights gained from studying its ATP synthase could be applied to related pathogenic bacteria where ATP synthase inhibition represents a viable therapeutic strategy .

What are common issues encountered during recombinant expression of ATP synthase subunits, and how can they be resolved?

Researchers frequently encounter several challenges when working with recombinant ATP synthase subunits that require specific troubleshooting approaches :

When expressing ATP synthase subunits, it's particularly important to verify correct membrane insertion using techniques like protease protection assays or fluorescence-based topology assays .

How can researchers validate that recombinantly produced D. oleovorans ATP synthase subunits are correctly folded and functional?

Validating correct folding and functionality of recombinant ATP synthase subunits requires multiple complementary approaches :

• Structural validation:

  • Circular dichroism to confirm secondary structure content

  • Fluorescence spectroscopy to assess tertiary structure

  • Limited proteolysis to verify compact folding

  • Size exclusion chromatography to detect aggregation

• Functional validation:

  • ATP hydrolysis activity using enzyme-coupled assays

  • DCCD binding to essential carboxyl residues

  • Reconstitution into liposomes and proton pumping assays

  • Blue-native PAGE with in-gel activity staining

• Interaction validation:

  • Co-purification with known partner subunits

  • Surface plasmon resonance with purified interaction partners

  • Microscale thermophoresis to measure binding affinities

  • Cross-linking mass spectrometry to map interaction sites

• Comparison with native enzyme:

  • Side-by-side activity measurements

  • Inhibitor sensitivity profiles

  • Thermal stability characteristics

  • Structural parameters from biophysical techniques

Correctly folded and functional recombinant ATP synthase components should exhibit similar properties to the native protein complex, including appropriate secondary structure content, thermal stability, and catalytic activity parameters .

What strategies can be employed to improve stability and storage of purified recombinant ATP synthase subunits?

Maintaining stability of purified ATP synthase subunits is critical for downstream applications. Several effective strategies have been developed :

• Buffer optimization:

  • Include glycerol (20-50%) as a stabilizing agent

  • Maintain pH near physiological range (pH 7.0-8.0)

  • Add specific lipids (0.05-0.1 mg/mL) that co-purify with native enzyme

  • Include reducing agents (DTT or TCEP) to prevent oxidation

• Storage conditions:

  • Store at -80°C for long-term preservation

  • Avoid repeated freeze-thaw cycles

  • Aliquot into single-use volumes before freezing

  • For short-term storage (1 week), keep at 4°C

• Stabilizing additives:

  • Specific detergents above critical micelle concentration

  • Amphipols or nanodiscs for detergent-free storage

  • Sucrose or trehalose (5-10%) as cryoprotectants

  • ATP or non-hydrolyzable analogs for conformational stability

• Preservation methods:

  • Flash freezing in liquid nitrogen

  • Lyophilization with appropriate protectants

  • Reconstitution into proteoliposomes

  • Immobilization on solid supports

Recommended storage buffer: 50 mM Tris-HCl pH 8.0, 100 mM NaCl, 5 mM MgCl2, 0.05% DDM, 50% glycerol, 1 mM DTT. This formulation maintains protein stability for up to 12 months at -80°C with retention of >80% activity .

What emerging technologies could enhance our understanding of ATP synthase structure and function?

Several cutting-edge technologies are poised to transform ATP synthase research :

• Advanced cryo-EM approaches:

  • Time-resolved cryo-EM to capture different conformational states

  • Cryo-electron tomography for in situ structural studies

  • Microcrystal electron diffraction for high-resolution details

  • Implications: Visualizing conformational changes during ATP synthesis/hydrolysis

• Single-molecule techniques:

  • Magnetic tweezers to measure torque generation

  • FRET-based approaches to track subunit movements

  • High-speed AFM to observe rotational dynamics

  • Implications: Directly observing molecular mechanisms of energy conversion

• Computational approaches:

  • Enhanced molecular dynamics simulations of complete ATP synthase

  • Machine learning for predicting functional impacts of mutations

  • Quantum mechanical calculations of proton transfer events

  • Implications: Modeling energetics and dynamics at atomic resolution

• Synthetic biology approaches:

  • De novo design of artificial ATP synthases

  • Incorporation of non-canonical amino acids for specialized functions

  • Creation of hybrid energy-converting enzymes

  • Implications: Engineering novel energy conversion systems with enhanced properties

• In-cell structural biology:

  • Correlative light and electron microscopy (CLEM)

  • In-cell NMR and EPR spectroscopy

  • Proximity labeling approaches (BioID, APEX)

  • Implications: Understanding ATP synthase function in its native environment

These technologies will provide unprecedented insights into the molecular mechanisms of ATP synthesis and the adaptations present in specialized organisms like D. oleovorans .

How might comparative studies of ATP synthases from different organisms enhance our understanding of D. oleovorans atpF1?

Comparative studies of ATP synthases across diverse organisms can provide critical insights into D. oleovorans atpF1 function and evolution :

• Evolutionary analysis approaches:

  • Phylogenetic reconstruction of ATP synthase subunit evolution

  • Identification of conserved versus variable regions

  • Correlation of sequence variations with environmental adaptations

  • Implications: Understanding selective pressures on ATP synthase design

• Structural comparison methodologies:

  • Superposition of ATP synthase structures from different domains of life

  • Mapping of conservation onto structural models

  • Analysis of interfaces between subunits across species

  • Implications: Identifying critical structural features versus adaptive variations

• Functional comparative studies:

  • Side-by-side biochemical analysis of ATP synthases from diverse organisms

  • Characterization under varied conditions (pH, temperature, salt)

  • Inhibitor sensitivity profiles across species

  • Implications: Correlating structural differences with functional adaptations

• Hybrid enzyme approaches:

  • Creation of chimeric ATP synthases with subunits from different species

  • Systematic replacement of domains to map compatibility

  • Directed evolution to enhance specific properties

  • Implications: Identifying functional modules and compatibility requirements

Particularly valuable would be comparisons between D. oleovorans ATP synthase and those from other extremophiles, closely related deltaproteobacteria, and model organisms like E. coli, allowing researchers to identify unique adaptations versus conserved features .

What are the potential applications of engineered ATP synthases containing modified D. oleovorans components?

Engineered ATP synthases incorporating D. oleovorans components have several promising applications in biotechnology and medicine :

• Bioenergy applications:

  • Engineering ATP synthases for enhanced efficiency

  • Creating hybrid energy-harvesting systems

  • Developing biological fuel cells

  • Research approach: Incorporate D. oleovorans ATP synthase components optimized for specific conditions

• Nanomotor development:

  • Utilizing the rotary mechanism for engineered nanomachines

  • Creating ATP-powered molecular devices

  • Developing controllable biological motors

  • Research approach: Modify b subunits to create customized peripheral stalks with altered mechanical properties

• Biosensing platforms:

  • ATP synthase-based sensors for environmental contaminants

  • Detection systems for inhibitory compounds

  • Monitoring of energy metabolism in real-time

  • Research approach: Engineer recognition domains into peripheral subunits

• Drug development platforms:

  • Screening systems for antimicrobial discovery

  • Structure-based drug design targeting bacterial ATP synthases

  • Development of species-selective inhibitors

  • Research approach: Use D. oleovorans components to understand bacterial-specific features

• Synthetic cell development:

  • Integration into artificial cell systems

  • Creation of minimal viable energy-generating systems

  • Development of orthogonal energy metabolism

  • Research approach: Simplify the ATP synthase complex to essential components

These applications build on the unique properties of D. oleovorans ATP synthase, particularly its adaptation to specialized environmental conditions and its distinct subunit characteristics .