Recombinant Opitutus terrae ATP synthase subunit b (atpF)

What is the structure and function of Opitutus terrae ATP synthase subunit b (atpF)?

The ATP synthase subunit b (atpF) from Opitutus terrae is a peripheral stalk component that connects the membrane-embedded F0 sector to the catalytic F1 sector of the ATP synthase complex. According to sequence data, it consists of 185 amino acids with the following sequence: mLPLFLAAAEAHVAEPGLVAELVEKFGLDPKYILIQTFSFLIVLGILYRFAIKPTIAAMEERAEKVGAGLKYAEEMQAKLAAAAQQESAAIVKKSQVEASRIVDEARRTAKDYLDKQTQEAAAKASETIAKAQQAIELEHRKmLADARTEIARLVVITTERVLAQKLSDSDRAAYNASATRELTNV .

Functionally, subunit b is essential for the structural integrity of the ATP synthase complex, providing stability during the rotational catalysis. It serves as part of the stator structure that prevents rotation of specific components while allowing others to rotate during ATP synthesis or hydrolysis. In bacterial ATP synthases, which are simpler than their mitochondrial counterparts, the subunit b plays a crucial role in the enzyme's ability to perform its core functions of ATP synthesis driven by transmembrane proton motive force .

What is known about the gene organization and expression of atpF in Opitutus terrae?

The atpF gene in Opitutus terrae is identified by the locus name Oter_0879 in its genome . While specific information about the gene organization in O. terrae is limited, in most bacteria, ATP synthase genes are typically organized in operons. The expression region of the recombinant protein has been identified as amino acids 1-185, representing the full-length protein .

What expression systems are optimal for producing recombinant Opitutus terrae ATP synthase subunit b?

Based on general practices for bacterial ATP synthase components and the information available for similar proteins, Escherichia coli represents an optimal expression system for recombinant O. terrae ATP synthase subunit b. E. coli has been successfully used to express ATP synthases from other bacterial species, such as Bacillus PS3 .

A methodological approach would involve:

• Gene synthesis or PCR amplification of the atpF gene from O. terrae genomic DNA

• Cloning into an expression vector with an appropriate promoter (T7 is commonly used)

• Adding a purification tag (His-tag or GST) if desired

• Transformation into an E. coli expression strain (BL21(DE3) or derivatives)

• Optimizing expression conditions (temperature, IPTG concentration, duration)

Expression may be enhanced by using codon-optimized sequences for E. coli and considering specialized strains for membrane-associated proteins if the hydrophobic regions of subunit b cause expression difficulties.

What purification strategies yield the highest purity and activity of recombinant Opitutus terrae ATP synthase subunit b?

Purification of recombinant O. terrae ATP synthase subunit b should consider its physical-chemical properties. Based on successful purification of other ATP synthase components, a multi-step purification process is recommended:

• Affinity chromatography: If expressed with a His-tag, immobilized metal affinity chromatography (IMAC) using Ni-NTA resin would be the first step

• Ion exchange chromatography: Based on the predicted isoelectric point of the protein

• Size exclusion chromatography: As a polishing step to remove aggregates and impurities

The purification buffer should be optimized to maintain protein stability. For storage, a Tris-based buffer containing 50% glycerol has been reported as suitable for the recombinant protein . Throughout purification, it's advisable to monitor protein purity by SDS-PAGE and activity by reconstitution into liposomes if functional studies are planned.

How should recombinant Opitutus terrae ATP synthase subunit b be stored to maintain structural integrity?

According to product information, recombinant O. terrae ATP synthase subunit b should be stored in a Tris-based buffer supplemented with 50% glycerol . For short-term storage, 4°C is suitable for up to one week. For extended storage, temperatures of -20°C or -80°C are recommended .

To avoid protein degradation:

• Aliquot the purified protein to avoid repeated freeze-thaw cycles

• Include protease inhibitors in storage buffers if degradation is observed

• Ensure sterile conditions to prevent microbial contamination

• Consider flash-freezing in liquid nitrogen before transferring to -80°C for long-term storage

It's important to note that repeated freezing and thawing is not recommended as it can lead to protein denaturation and loss of activity .

How can recombinant Opitutus terrae ATP synthase subunit b be used in structural studies?

Structural studies of recombinant O. terrae ATP synthase subunit b can be approached through several complementary techniques:

• Cryo-electron microscopy (cryo-EM): This technique has been successfully applied to ATP synthases, revealing atomic models in different rotational states . For studying the O. terrae subunit b specifically, it could be incorporated into reconstituted ATP synthase complexes for structural analysis.

• X-ray crystallography: While challenging due to the partially hydrophobic nature of the protein, crystallography could provide high-resolution structural information if suitable crystals can be obtained.

• Nuclear Magnetic Resonance (NMR): For studying specific domains or interactions, particularly for the soluble portions of the protein.

• Small-angle X-ray scattering (SAXS): To obtain low-resolution structural information in solution.

The methodological workflow would involve:

• Expression and purification of the protein with high purity

• Biochemical characterization (size, oligomeric state)

• Optimization of buffer conditions for structural studies

• Application of the chosen structural technique

• Data collection and processing

• Model building and refinement

What functional assays can be used to study recombinant Opitutus terrae ATP synthase subunit b?

While subunit b itself does not possess enzymatic activity, its functional role can be assessed through:

• Reconstitution assays: Incorporating recombinant subunit b into ATP synthase complexes lacking this component to restore function. This could be performed using purified subunits or in membrane reconstitution systems.

• Protein-protein interaction studies:

  • Pull-down assays to identify binding partners

  • Surface plasmon resonance (SPR) to measure binding affinities

  • Cross-linking studies to map interaction interfaces

• ATP synthesis/hydrolysis assays after reconstitution:

  • ATP synthesis can be measured in reconstituted liposomes by applying artificial driving forces (proton or sodium gradients)

  • Rates can be quantified in nmol·min⁻¹·mg protein⁻¹

A useful experimental approach would be to reconstitute ATP synthase with wild-type or mutant subunit b variants and measure ATP synthesis rates under various conditions to assess the impact of specific residues or domains on function.

How can site-directed mutagenesis be applied to study Opitutus terrae ATP synthase subunit b?

Site-directed mutagenesis represents a powerful approach for structure-function studies of O. terrae ATP synthase subunit b. Based on the provided amino acid sequence , several strategies can be employed:

• Identification of target residues:

  • Conserved residues through multiple sequence alignment with other bacterial species

  • Charged residues potentially involved in protein-protein interactions

  • Hydrophobic residues that might contribute to membrane association

• Types of mutations to consider:

  • Alanine scanning to assess the importance of specific side chains

  • Conservative substitutions to test the role of particular chemical properties

  • Introduction of cysteine residues for cross-linking or fluorescent labeling

• Methodological workflow:

  • PCR-based site-directed mutagenesis

  • Verification by sequencing

  • Expression and purification of mutant proteins

  • Functional characterization through reconstitution assays

  • Structural analysis of the effects of mutations

How does the structure of Opitutus terrae ATP synthase subunit b relate to its role in the stator complex?

The structure-function relationship of O. terrae ATP synthase subunit b in the stator complex requires advanced structural biology approaches. While specific structural data for the O. terrae protein is not available, insights can be gained from homology modeling and comparative analysis with related proteins.

Methodological approach:

• Generate a homology model based on the known structures of bacterial ATP synthase subunit b proteins

• Analyze the model for:

  • Hydrophobic regions that may interact with the membrane

  • Coiled-coil domains that might interact with other stator components

  • Regions that interact with the F1 sector

The sequence analysis suggests potential structural features. For example, the N-terminal region (mLPLFLAAAEAHVAEPGLVAELVEK...) contains hydrophobic residues that might anchor the protein in the membrane, while later segments show patterns consistent with coiled-coil structures that could interact with other subunits .

Cross-linking studies combined with mass spectrometry could experimentally validate these predictions by identifying interaction partners and specific contact points within the ATP synthase complex.

What is the role of proton/sodium translocation in ATP synthases containing Opitutus terrae components?

The mechanism of ion translocation in ATP synthases is fundamental to their function. While specific information about the ion specificity of O. terrae ATP synthase is not provided in the search results, methodological approaches to investigate this question would include:

• Reconstitution experiments:

  • Incorporation of recombinant O. terrae ATP synthase components into liposomes

  • Measurement of ATP synthesis under varying ion gradients (H⁺ vs. Na⁺)

  • Assessment of coupling efficiency under different conditions

• Site-directed mutagenesis of key residues:

  • Identification of potential ion-binding sites through sequence analysis

  • Mutation of these residues and functional testing

  • Measurement of ion selectivity changes

• Structural analysis focused on the ion channel:

  • Cryo-EM studies of the assembled complex with focus on the F0 sector

  • Molecular dynamics simulations to understand ion movement

From general ATP synthase research, we know that ion translocation occurs through the membrane-embedded F0 sector and drives the rotation of the central stalk, which in turn drives conformational changes in the F1 sector leading to ATP synthesis . The specific pathways and residues involved in O. terrae ATP synthase would be a valuable research target.

How can cryo-EM contribute to understanding the dynamics of ATP synthases with Opitutus terrae components?

Cryo-electron microscopy (cryo-EM) has revolutionized our understanding of ATP synthases by enabling visualization of these complexes in different rotational states at near-atomic resolution . For studying ATP synthases containing O. terrae components, cryo-EM offers several advantages:

• Methodological approach for structural studies:

  • Expression and purification of O. terrae ATP synthase components

  • Reconstitution of functional complexes

  • Sample vitrification and data collection

  • Image processing to identify different conformational states

  • Model building and refinement

• Potential insights from cryo-EM studies:

  • Visualization of different rotational states (similar to the three states observed in Bacillus PS3 ATP synthase)

  • Understanding of how subunit b contributes to the stator function

  • Identification of unique structural features compared to other bacterial ATP synthases

  • Insights into the mechanism of coupling proton translocation to ATP synthesis

• Technical considerations:

  • Use of detergent or nanodisc reconstitution to stabilize the membrane domain

  • Application of classification methods to sort different conformational states

  • Focused refinement on specific regions of interest

Such studies could reveal how the O. terrae subunit b contributes to the architecture of the membrane region and how the enzyme performs its core functions .

How to address issues with protein solubility and stability during recombinant expression?

Recombinant expression of membrane-associated proteins like ATP synthase subunit b often presents solubility challenges. Based on the sequence characteristics of O. terrae ATP synthase subunit b and general principles for membrane protein expression, the following methodological approaches are recommended:

• Addressing poor expression:

  • Optimize codon usage for the expression host

  • Test different E. coli strains (C41/C43 specifically designed for membrane proteins)

  • Evaluate different induction temperatures (16-30°C)

  • Consider fusion partners (MBP, SUMO) to enhance solubility

• Improving protein solubility:

  • Test different detergents for extraction (DDM, LDAO, Triton X-100)

  • Consider expressing only the soluble domain for certain applications

  • Evaluate the effect of additives like glycerol or specific ions

  • Test different pH and salt concentrations in extraction buffers

• Enhancing stability:

  • Include protease inhibitors during purification

  • Maintain cold temperatures throughout the process

  • Add stabilizing agents in storage buffers (glycerol as recommended for this protein)

  • Consider storage in smaller aliquots to avoid freeze-thaw cycles

When working specifically with O. terrae ATP synthase subunit b, the recommended storage in Tris-based buffer with 50% glycerol at -20°C or -80°C should be followed to maintain stability .

What strategies can overcome challenges in reconstituting ATP synthase complexes with Opitutus terrae subunit b?

Reconstitution of functional ATP synthase complexes represents a significant challenge. Based on successful approaches with other ATP synthases, the following methodological strategies are recommended:

• Component preparation:

  • Ensure high purity of all subunits to be reconstituted

  • Maintain proteins in compatible detergents or buffers

  • Verify individual component integrity before assembly

• Assembly strategies:

  • Sequential addition of components based on known assembly pathways

  • Co-expression of multiple subunits in a single host

  • Test both detergent-based and liposome reconstitution methods

• Specific challenges with ATP synthase reconstitution:

  • Establish correct orientation in liposomes (F1 facing outward)

  • Maintain the integrity of the proton channel

  • Ensure proper assembly of the stator components

• Verification of successful reconstitution:

  • Electron microscopy to verify complex formation

  • ATP synthesis/hydrolysis assays with artificial proton gradients

  • Proton pumping assays with pH-sensitive fluorescent dyes

For ATP synthesis measurements, researchers can apply artificial driving forces through potassium diffusion potential using valinomycin, as demonstrated in studies with other ATP synthases . The reconstituted system can then be tested for ATP synthesis capacity by adding ADP and measuring ATP production rates.

How to troubleshoot experimental inconsistencies in functional assays involving Opitutus terrae ATP synthase?

Functional assays with reconstituted ATP synthases can yield variable results due to multiple factors. A systematic troubleshooting approach should include:

• Addressing variable ATP synthesis rates:

  • Verify the integrity of the proton/sodium gradient

  • Ensure consistent protein:lipid ratios in reconstitution

  • Control for temperature fluctuations during measurements

  • Verify ATP detection method calibration

• Resolving issues with coupling efficiency:

  • Test for leaky liposomes using ion-sensitive dyes

  • Verify the orientation of reconstituted complexes

  • Ensure complete assembly of all components

  • Check for inhibitory contaminants

• Improving data reproducibility:

  • Standardize protein preparation methods

  • Use internal controls for each experiment

  • Prepare fresh substrates for each experiment

  • Consider multiple technical and biological replicates

Based on approaches used for other ATP synthases, ATP synthesis can be measured by applying potassium diffusion potential (e.g., 160 mV) combined with ion gradients to generate total driving forces around 230 mV . Rates should be linear for initial periods (approximately 2 minutes) and can be quantified in nmol·min⁻¹·mg protein⁻¹ .