Recombinant Pseudomonas putida ATP synthase subunit b (atpF)

What is the structure and function of ATP synthase in Pseudomonas putida?

ATP synthase in P. putida functions as the "turbine" of the cell's power plants, producing adenosine triphosphate (ATP), which is the cellular energy currency essential for various metabolic processes. The enzyme operates by coupling the translocation of protons across the cell membrane, along an electrochemical gradient, to the mechanical rotation of subunits that drives ATP synthesis .

The ATP synthase complex consists of two main portions:

• The membrane-embedded F₀ portion (containing subunits a, b, and c)

• The catalytic F₁ portion (containing subunits α, β, γ, δ, and ε)

The b subunit (atpF) is part of the F₀ portion and serves as a critical stator component that connects the F₁ and F₀ portions, maintaining structural integrity during rotational catalysis .

How does ATP synthase contribute to P. putida's energy metabolism?

P. putida has evolved a unique metabolic architecture that allows for efficient energy generation. When growing on glucose, cells generate an ATP surplus, with ATP synthase playing a crucial role in this process. The oxidation pathway significantly contributes to ATP supply through the ATP synthase complex .

A notable characteristic of P. putida metabolism is the periplasmic oxidation steps from glucose to gluconate (GLN) and 2-ketogluconate (2KG), which release electrons that are coupled to ATP generation via the ATP synthase. This allows P. putida to circumvent the direct ATP-costly glucose uptake via the ABC transporter (GtsABCD) system and partially uncouple ATP formation from NADH formation .

Why is P. putida ATP synthase of particular interest for research?

P. putida ATP synthase has gained research interest due to several factors:

• Role in stress tolerance: ATP synthase expression is modulated during adaptation to environmental stresses, particularly solvent exposure .

• Metabolic flexibility: P. putida demonstrates remarkable adaptability to different carbon sources, with ATP synthase playing a key role in energy balance during these transitions .

• Biotechnological applications: Understanding and manipulating ATP synthase can enhance P. putida's utility as a platform organism for various biotechnological applications .

• Energy optimization: ATP synthase regulation contributes to P. putida's natural energy surplus, making it an ideal candidate for metabolic engineering .

How does ATP synthase expression change under different stress conditions in P. putida?

Research has revealed complex regulation of ATP synthase in response to environmental stressors. In solvent-adapted strains of P. putida S12, transcriptomic analysis showed constitutive downregulation of energy-consuming activities, including F₀F₁ATP synthase, alongside flagellar assembly and membrane transport proteins .

During exposure to toluene stress, P. putida DOT-T1E cells exhibit increased expression of certain ABC transporters and inorganic pyrophosphatases involved in providing energetic support for stress response reactions, indirectly affecting ATP metabolism and potentially ATP synthase regulation .

Additionally, when P. putida KT2440 is exposed to repeated glucose shortage (simulating large-scale bioreactor heterogeneity), a stringent response-like transcriptional regulation program is induced. This response appears linked to the intracellular pool of 3-hydroxyalkanoates (3-HA), which are precursors for polyhydroxyalkanoates (PHA) . These metabolic shifts likely involve changes in ATP synthase activity to maintain energy homeostasis.

What approaches have been successful for recombinant expression of ATP synthase components?

While specific protocols for P. putida atpF are not directly detailed in the literature, successful approaches for recombinant expression of ATP synthase components from other organisms provide valuable methodological insights.

For example, the ATP synthase subunit c from spinach chloroplast was successfully produced using the following strategy:

• Gene synthesis: A synthetic gene was constructed by annealing and ligating overlapping oligonucleotides with optimized codon usage .

• Expression vector selection: Multiple vectors were tested, including:

  • pMAL-c2x (New England Biolabs)

  • pET-32a(+) (Novagen)

  • pFLAG-MAC (Sigma-Aldrich)

• Host strain optimization: E. coli T7 Express lysY/Iᵍ cells were used as the expression host .

• Co-expression with chaperones: To increase production of difficult-to-express proteins, co-transformation with plasmids expressing chaperone proteins (DnaK, DnaJ, and GrpE) significantly improved yields .

This multi-vector approach allows for comparing different expression strategies and identifying optimal conditions for producing functional ATP synthase components.

What role does ATP synthase play in P. putida's adaptation to solvent stress?

Research on solvent-tolerant P. putida strains has revealed that ATP synthase regulation is part of a complex adaptive response to organic solvents. In P. putida S12, adaptation to solvent exposure involved multiple genetic changes .

After adaptive laboratory evolution (ALE) to restore solvent tolerance in plasmid-cured P. putida S12, researchers identified specific mutations in:

• The intergenic region and subunits of ATP synthase

• RNA polymerase subunit β′

• Global two-component regulatory system (GacA/GacS)

• A putative AraC family transcriptional regulator (Afr)

Transcriptomic analysis further revealed constitutive downregulation of energy-consuming activities, including F₀F₁ATP synthase. This suggests that modulating energy conservation through ATP synthase regulation is a key component of the solvent tolerance mechanism .

These findings indicate that ATP synthase not only serves as a primary energy generation system but also as a regulatory target during adaptation to environmental stressors.

How can genome editing techniques be applied to study ATP synthase function in P. putida?

A variety of advanced genome editing technologies have been developed for P. putida that can be applied to study ATP synthase subunits:

• CRISPR/Cas9-based technologies:

  • Efficient curing of helper plasmids

  • Counterselection of infrequent mutations created through recombineering

  • CRISPR interference-mediated gene regulation

• I-SceI-based genome editing system:

  • Uses suicide plasmid pEMG with recognition sequences for I-SceI homing endonuclease

  • Conditional expression of I-SceI introduces double-stranded breaks

  • Allows for gene deletion, insertion, and replacement through homologous recombination

• RecET-based markerless recombineering:

  • Enables deletion and integration of large-sized genes and clusters

• Thermoinducible single-stranded recombineering system:

  • Allows for precise, small-scale genomic modifications

These technologies enable precise manipulation of ATP synthase subunit genes to study their role in energy metabolism, stress responses, and potential applications in metabolic engineering.

What expression systems are most effective for producing recombinant P. putida ATP synthase components?

Several expression systems have shown promise for the recombinant production of membrane proteins like ATP synthase components:

For challenging membrane proteins like ATP synthase subunits, co-expression with chaperone proteins (DnaK, DnaJ, and GrpE) has been shown to substantially increase production yields .

When using P. putida itself as the expression host, the Standard European Vector Architecture (SEVA) platform provides modular vectors specifically designed for this organism . This approach may be advantageous for maintaining native conformation and function of ATP synthase components.

What purification strategies yield functional ATP synthase subunits?

Purification of recombinant ATP synthase subunits presents significant challenges due to their hydrophobic nature and membrane association. Based on successful purification of related proteins, the following strategy is recommended:

• Affinity purification using appropriate tags:

  • His-tag for IMAC purification

  • MBP fusion for amylose resin purification

  • FLAG-tag for immunoaffinity purification

• Detergent solubilization optimization:

  • Screen multiple detergents (DDM, LDAO, OG)

  • Test various detergent concentrations

  • Assess different solubilization temperatures and times

• Size exclusion chromatography:

  • Further purification step

  • Assessment of oligomeric state

  • Buffer optimization for stability

• Functional validation:

  • ATP hydrolysis assays

  • Reconstitution into liposomes

  • Interaction studies with other ATP synthase subunits

The choice of detergent is particularly critical for maintaining structural integrity and function of membrane-associated subunits like atpF.

How can genetic modifications of ATP synthase improve P. putida's biotechnological applications?

Strategic modification of ATP synthase genes could enhance P. putida's utility as a biotechnological chassis in several ways:

• Improving solvent tolerance:

  • Based on findings that solvent-adapted strains show altered ATP synthase expression, targeted modifications could enhance tolerance to organic solvents .

  • This would be valuable for bioremediation applications and production of toxic compounds.

• Enhancing energy efficiency:

  • Modulating ATP synthase expression could optimize the cellular energy balance for specific bioprocesses .

  • Studies have shown that P. putida can generate an ATP surplus during growth on glucose, which could be enhanced or redirected through ATP synthase modifications.

• Stress resistance optimization:

  • ATP synthase regulation is linked to various stress responses, including solvent exposure, nutrient limitation, and oxidative stress .

  • Engineered variants could enhance resistance to industrial bioprocess conditions.

• Metabolic pathway optimization:

  • For heterologous production of compounds like prodigiosin and glidobactin A, disruptions in the electron transport chain components (which are functionally linked to ATP synthase) led to improved production .

  • This suggests that strategic ATP synthase modifications could enhance production of valuable biomolecules.

Implementation approach:

• Identify specific ATP synthase variants from adaptive laboratory evolution experiments

• Use CRISPR/Cas9 or recombineering for precise genomic modifications

• Validate engineered strains under relevant bioprocess conditions

What analytical methods are most informative for studying P. putida ATP synthase function?

To comprehensively characterize ATP synthase function in P. putida, a multi-faceted analytical approach is recommended:

For transcriptomic analysis, RNA-seq has been successfully applied to understand ATP synthase regulation in solvent-adapted P. putida strains, revealing downregulation as part of the adaptive response .

Proteomic approaches using two-dimensional gel electrophoresis followed by mass spectrometry have been effective in identifying changes in energy metabolism proteins (including ATP synthase components) in response to environmental stressors like toluene exposure .

How can researchers optimize ATP synthase gene expression for heterologous production?

For optimal expression of ATP synthase genes in heterologous systems, several strategies have proven effective:

• Codon optimization:

  • Adapt the coding sequence to the preferred codon usage of the expression host

  • This is particularly important when expressing P. putida genes (61.5% GC content) in hosts with different GC content

• Promoter selection:

  • For expression in P. putida:

    • The XylS/Pm system (provides tight regulation)

    • The ChnR/PchnB system (offers inducible expression)

  • For expression in E. coli:

    • T7 promoter system for high-level expression

    • tac promoter for moderate expression levels

• Translation optimization:

  • Optimize ribosome binding sites

  • Consider inclusion of translational enhancers

  • Test different N-terminal fusion partners to enhance translation initiation

• Expression conditions:

  • Temperature: Lower temperatures (16-25°C) often yield higher amounts of functional membrane proteins

  • Induction timing: Induction at mid-log phase typically provides optimal balance between biomass and expression

  • Media composition: Rich media for high biomass or defined media for controlled induction

• Co-expression strategies:

  • Co-express with chaperone proteins (DnaK, DnaJ, GrpE) to enhance proper folding

  • Consider co-expression of other ATP synthase subunits for proper complex assembly

These approaches can be systematically tested using the multi-vector strategy described in section 2.2 to identify optimal conditions for producing functional ATP synthase components.

What are the major challenges in studying recombinant P. putida ATP synthase subunits?

Researchers face several significant challenges when working with recombinant ATP synthase subunits:

• Membrane protein expression hurdles:

  • Hydrophobic nature complicates expression and purification

  • Potential toxicity to host cells during overexpression

  • Proper membrane insertion and folding requirements

• Complex assembly considerations:

  • Individual subunits may behave differently outside the context of the complete ATP synthase complex

  • Multi-subunit assembly requires coordinated expression of multiple genes

  • Native lipid environment may be crucial for proper function

• Functional assessment limitations:

  • Difficult to measure activity of individual subunits

  • Complete ATP synthase complex typically required for ATP synthesis activity

  • Reconstitution into artificial membrane systems adds complexity

• Post-translational modifications:

  • Evidence suggests various post-translational modifications of ATP synthase subunits

  • Five different spots identified as TodC1 (another P. putida protein) on 2D gels correspond to different post-translational modifications

  • Similar modifications may occur in ATP synthase subunits, affecting function

How might ATP synthase engineering contribute to P. putida strain improvement?

ATP synthase engineering represents a promising frontier for enhancing P. putida's industrial applications:

• Enhanced bioremediation capabilities:

  • Modulating ATP synthase expression could optimize energy allocation during breakdown of toxic compounds

  • In engineered strains capable of TCP (1,2,3-trichloropropane) degradation, improved intracellular energy charge (ATP/ADP ratio) enhanced biodegradation efficiency

• Optimized heterologous production:

  • Disruption of electron transport chain components, which are functionally linked to ATP synthase, improved production of bioactive compounds like prodigiosin

  • Strategic ATP synthase modifications could further enhance production capacity

• Expanded substrate utilization:

  • ATP synthase regulation is linked to carbon source adaptation

  • Engineering could enhance utilization of non-preferred substrates

  • This would be valuable for valorization of industrial waste streams

• Industrial robustness:

  • Engineered ATP synthase variants could enhance tolerance to industrial conditions

  • Particularly valuable for large-scale heterogeneous bioreactor environments where glucose limitation occurs frequently

Future strain improvement might combine ATP synthase modifications with other beneficial genetic changes, such as deletion of flagella-related genes, which has been shown to improve intracellular energy charge (ATP/ADP ratio) and reducing power (NADPH/NADP+ ratio) .

What are emerging technologies that could advance P. putida ATP synthase research?

Several cutting-edge technologies show promise for advancing ATP synthase research:

• Cryo-electron microscopy (cryo-EM):

  • Enables high-resolution structural analysis of membrane protein complexes

  • Could reveal unique structural features of P. putida ATP synthase

  • May identify structural basis for adaptation to different environmental conditions

• Advanced genome editing tools:

  • CRISPR interference (CRISPRi) for fine-tuned gene regulation

  • Base editing for precise single nucleotide modifications

  • Prime editing for targeted insertions and deletions without double-strand breaks

• Microfluidic systems:

  • Allow for precise control of microenvironments

  • Enable real-time monitoring of single-cell responses

  • Valuable for studying ATP synthase function under dynamic conditions

• Synthetic biology approaches:

  • De novo design of ATP synthase variants with enhanced properties

  • Creation of minimal ATP synthase systems

  • Development of biosensors for ATP production and energy homeostasis

These technologies, combined with the growing synthetic biology toolkit for P. putida, provide unprecedented opportunities for understanding and engineering ATP synthase for various applications.