Recombinant Pelodictyon luteolum ATP synthase subunit b 2 (atpF2)

How is recombinant Pelodictyon luteolum atpF2 typically expressed and purified?

The recombinant P. luteolum atpF2 protein is typically expressed in E. coli expression systems with an N-terminal His-tag to facilitate purification . The methodological approach involves:

• Cloning: The atpF2 gene sequence (corresponding to amino acids 1-175) is cloned into a bacterial expression vector with an N-terminal His-tag.

• Expression: Transformation into E. coli expression strain followed by induction of protein expression under optimized conditions.

• Purification:

  • Bacterial cell lysis using mechanical disruption or chemical methods

  • Immobilized metal affinity chromatography (IMAC) using the His-tag

  • Size exclusion chromatography for further purification if needed

  • Validation of purity by SDS-PAGE (>90% purity is typically achieved)

• Lyophilization: The purified protein is often provided as a lyophilized powder to enhance stability during storage .

What are the optimal storage conditions for recombinant atpF2 protein?

For optimal stability and activity of recombinant P. luteolum atpF2, the following storage conditions are recommended:

It's important to note that repeated freeze-thaw cycles should be avoided to maintain protein integrity. After reconstitution, the protein should be centrifuged briefly before opening to bring contents to the bottom of the vial .

How does P. luteolum atpF2 differ from other bacterial ATP synthase b subunits?

While P. luteolum atpF2 shares functional similarity with other bacterial ATP synthase b subunits, it has several distinctive features:

• Sequence characteristics: The P. luteolum atpF2 contains distinctive hydrophobic N-terminal regions for membrane anchoring and charged C-terminal regions for interaction with other subunits of the ATP synthase complex .

• Copy number in the complex: Unlike some bacteria that have a single copy of subunit b, P. luteolum contains two forms (atpF2 being the second form), suggesting specialized roles in the ATP synthase complex or differential regulation .

• Genomic organization: The atpF2 gene (designated as Plut_2096) is found in proximity to atpB2 (Plut_2098), suggesting a coordinated expression of these components .

The distinct characteristics of atpF2 may reflect adaptations to the environmental conditions experienced by P. luteolum as a green sulfur bacterium.

What methodologies can be used to study the assembly of ATP synthase complexes using recombinant atpF2?

Investigating ATP synthase assembly using recombinant atpF2 requires sophisticated methodological approaches:

• Blue Native-PAGE (BN-PAGE):

  • Mix recombinant atpF2 with other purified ATP synthase subunits at controlled ratios

  • Analyze the formation of subcomplexes and full complexes using BN-PAGE

  • Confirm assembled complexes using in-gel activity assays with ATP hydrolysis measurements

• Time-resolved assembly studies:

  • Add fluorescently-labeled atpF2 to partially assembled complexes

  • Track incorporation using FRET-based assays or single-molecule fluorescence

  • Identify assembly intermediates and kinetics of integration

• Cryo-electron microscopy (cryo-EM):

  • Reconstitute atpF2 with other subunits to form assembled complexes

  • Perform cryo-EM analysis to visualize assembly intermediates

  • Generate 3D models of assembly states at different time points

• Cross-linking mass spectrometry:

  • Introduce chemical cross-linkers during assembly process

  • Identify interaction interfaces using mass spectrometry

  • Map the temporal sequence of protein-protein interactions during assembly

Research suggests that the assembly of ATP synthase follows a specific path: the F1-c8 complex with peripheral stalk components (including homologs of atpF2) forms a template for insertion of membrane-encoded subunits, followed by association of additional components to stabilize the complex .

How can P. luteolum atpF2 be functionally reconstituted into liposomes for bioenergetic studies?

Functional reconstitution of P. luteolum atpF2 into liposomes for bioenergetic studies involves several critical steps:

• Preparation of proteoliposomes:

  • Prepare liposomes from phospholipids (typically a mixture of phosphatidylcholine, phosphatidylethanolamine, and cardiolipin)

  • Add recombinant atpF2 together with other ATP synthase subunits in detergent

  • Remove detergent gradually using Bio-Beads or dialysis

  • Confirm incorporation by density gradient centrifugation

• Functional validation:

  • Assess ATP hydrolysis activity using enzyme-coupled assays (e.g., pyruvate kinase/lactate dehydrogenase system)

  • Measure proton pumping using pH-sensitive fluorescent dyes (e.g., ACMA)

  • Evaluate ATP synthesis driven by artificially imposed ΔpH

• Electrophysiological measurements:

  • Incorporate proteoliposomes into planar lipid bilayers

  • Record ion conductance under different conditions (pH, membrane potential, presence of inhibitors)

  • Assess the effect of Ca²⁺ on membrane permeability

One study demonstrated that when purified ATP synthase was incorporated into liposomes, Ca²⁺ could dissipate the H⁺ gradient generated by ATP hydrolysis, suggesting a dual role of ATP synthase in both energy conservation and dissipation under certain conditions .

What approaches can be used to study the phosphorylation of ATP synthase b subunits and its impact on function?

While specific phosphorylation of P. luteolum atpF2 has not been directly reported, studies on ATP synthase β subunit phosphorylation provide valuable methodological insights applicable to investigating potential atpF2 phosphorylation:

• Identification of phosphorylation sites:

  • In silico analysis to predict potential phosphorylation sites

  • Mass spectrometry-based phosphoproteomic analysis

  • ³²P labeling experiments using γ³²P-ATP to detect phosphorylation events

• Site-directed mutagenesis approaches:

  • Generate phospho-mimetic mutations (S/T→D/E) and non-phosphorylatable mutations (S/T→A)

  • Express and purify mutant proteins

  • Assess impact on structure and function

• Functional impact assessment:

  • Measure ATPase activity of phospho-mutants

  • Assess complex assembly using BN-PAGE

  • Examine supercomplex formation

One study on ATP synthase β subunit demonstrated that phosphorylation can significantly impact enzyme function. For example, a phospho-mimetic mutation at T262 (T262E) abolished ATPase activity, while the non-phosphorylatable mutant (T262A) maintained wild-type activity levels:

This demonstrates how phosphorylation at specific sites can serve as a regulatory mechanism for ATP synthase function .

How can fluorescent ATP sensors be used to study P. luteolum ATP synthase activity in reconstituted systems?

Advanced fluorescent ATP sensors provide powerful tools for studying ATP synthase activity in real-time:

• Application of genetically encoded ATP sensors:

  • The recently developed iATPSnFR2 sensor (a circularly permuted GFP inserted between ATP-binding helices of the ε-subunit of bacterial F₀-F₁ ATPase) offers 5-6 fold improvement in dynamic range compared to previous sensors

  • Affinity variants are available with Kd values ranging from 4 μM to 500 μM

  • Chimeric versions fused to HaloTag provide ratiometric readout

• Experimental setup for ATP synthase activity monitoring:

  • Reconstitute P. luteolum ATP synthase containing atpF2 into liposomes

  • Include purified ATP sensor proteins in the liposomal lumen

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

  • Monitor real-time ATP production via fluorescence changes

• Inhibitor studies:

  • Examine effects of specific inhibitors like oligomycin on ATP production

  • Test the impact of atpF2 mutations on inhibitor sensitivity

  • Investigate the role of Ca²⁺ in modulating ATP synthase function

This approach allows for quantitative assessment of ATP production rates and reveals how structural alterations in atpF2 or other subunits affect the catalytic efficiency of the complete ATP synthase complex.

What role does atpF2 play in ATP synthase dimerization and higher-order organization?

ATP synthase dimerization and oligomerization are critical for mitochondrial cristae formation, though less is known about this process in bacterial systems like P. luteolum:

• Investigation of dimerization interfaces:

  • Crosslinking studies to identify contact points between adjacent ATP synthase complexes

  • Cryo-EM analysis of dimeric/oligomeric forms

  • Mutagenesis of potential interface residues in atpF2 to assess impact on dimerization

• Functional implications of dimerization:

  • Compare ATP synthesis/hydrolysis rates between monomeric and dimeric forms

  • Assess proton conductance in reconstituted systems

  • Examine calcium-induced channel formation in dimers vs. monomers

Research on eukaryotic ATP synthase suggests that dimers and oligomers, but not monomers, can form calcium-activated channels that may be involved in cell death mechanisms. This raises interesting questions about whether bacterial ATP synthases containing atpF2 might have similar properties .

Studies of human ATP synthase assembly have shown that dimerization occurs late in the assembly process, after incorporation of mitochondrially-encoded subunits. A similar sequential assembly might occur in bacterial systems, with atpF2 potentially playing a role in stabilizing interactions between adjacent complexes .

How can CRISPR-based approaches be used to study the function of ATP synthase genes in their native context?

While CRISPR-based genome editing of P. luteolum has not been specifically reported, general methodological approaches applicable to studying atpF2 function include:

• CRISPR-Cas9 genome editing strategies:

  • Design guide RNAs targeting the atpF2 gene

  • Prepare repair templates for introducing specific mutations

  • Optimize transformation protocols for P. luteolum or related green sulfur bacteria

  • Screen for successful genome modifications using PCR and sequencing

• CRISPR interference (CRISPRi) for gene knockdown:

  • Express catalytically inactive Cas9 (dCas9) with guide RNAs targeting atpF2

  • Titrate expression levels to achieve partial knockdown

  • Monitor effects on ATP synthesis and bacterial growth

  • Compare with knockdown of other ATP synthase components

• Rescue experiments with recombinant protein:

  • Generate atpF2 knockout strains

  • Complement with recombinant wildtype or mutant versions

  • Assess restoration of ATP synthase function

  • Identify critical residues for in vivo function

These approaches can provide insights into the function of atpF2 in its native cellular context that complement in vitro studies with the recombinant protein.

What is the impact of temperature on ATP synthase activity and how can this be studied using recombinant atpF2?

Temperature significantly affects ATP synthase activity, and recombinant atpF2 can be used to investigate these effects:

• Temperature-dependent activity assays:

  • Reconstitute ATP synthase complexes containing recombinant atpF2

  • Measure ATP synthesis and hydrolysis rates across temperature range (15-40°C)

  • Assess oxygen consumption rates in parallel

  • Generate Arrhenius plots to determine activation energies

• Thermostability studies:

  • Use differential scanning calorimetry (DSC) or thermal shift assays

  • Compare wildtype atpF2 with thermostable mutants

  • Identify temperature-sensitive regions within the protein

• Structural changes with temperature:

  • Apply circular dichroism (CD) spectroscopy to monitor secondary structure

  • Use hydrogen-deuterium exchange mass spectrometry to identify flexible regions

  • Compare thermal behavior of isolated atpF2 with assembled complexes

AP Biology data showed that temperature significantly impacts both oxygen consumption and ATP synthesis rates in toad liver cells:

This data demonstrates the bell-shaped curve relationship between temperature and ATP synthase activity, with activity peaking around 30°C but decreasing at higher temperatures due to protein denaturation .

How does the assembly of ATP synthase containing atpF2 compare to the assembly pathway of human mitochondrial ATP synthase?

Assembly of ATP synthase is a complex, stepwise process that differs between species:

• Comparative assembly analysis:

  • Express fluorescently tagged atpF2 and human homologs

  • Monitor incorporation into nascent complexes

  • Identify key intermediate complexes using BN-PAGE

  • Compare assembly factors required in each system

• Role of assembly factors:

  • The human ATPAF2 (ATP12) protein serves as an assembly factor for the F1 component

  • Investigate whether P. luteolum has analogous assembly factors

  • Test cross-species complementation of assembly pathways

• Assembly pathway comparison:

  • Human ATP synthase assembly involves:

    • Formation of F1-c8 complex inhibited by IF1

    • Attachment of peripheral stalk with subunits e, f, and g

    • Insertion of mitochondrially-encoded ATP6 and ATP8

    • Stabilization by the 6.8 proteolipid

    • Final dimerization and oligomerization

  • P. luteolum assembly likely follows similar principles but with bacterial-specific features

Human ATPAF2 mutations can cause mitochondrial Complex V deficiency, characterized by lactic acidosis, encephalopathy, and developmental delays. This highlights the critical importance of proper ATP synthase assembly for cellular function .