Recombinant Shewanella halifaxensis ATP synthase subunit b (atpF)

What is the basic structure and function of Shewanella halifaxensis ATP synthase subunit b (atpF)?

ATP synthase subunit b (atpF) in Shewanella halifaxensis is a key component of the F-type ATP synthase complex. The protein consists of 156 amino acids with the sequence: MSINATLLGQAISFLLFVWFCMKFVWPPLMNAIEERQKKIADGLADAGRAAKDLELAQVKATEQLKDAKATANEIIEQANKRKAQIVDEAKVEADTERAKIIAQGHAEIENERNRVKEDLRKQVAALAIAGAEKILERSIDEAAHSDIVNKLVAEL. The protein is also known by alternative names including ATP synthase F(0) sector subunit b, ATPase subunit I, and F-type ATPase subunit b. Its gene is designated as atpF with the ordered locus name Shal_4298 .

Functionally, ATP synthase subunit b forms part of the membrane-embedded F0 sector of the ATP synthase complex. This complex is central to the cellular energy generation process, utilizing the proton motive force to catalyze the synthesis of ATP. Within this complex, subunit b connects the membrane-embedded F0 portion to the catalytic F1 sector, serving as a critical structural element for the rotational mechanism of ATP synthesis.

How does Shewanella halifaxensis adapt to its cold marine environment, and how might this affect ATP synthase function?

Shewanella halifaxensis is a psychrophilic bacterium isolated from marine sediment near Halifax harbour in Canada. Like other psychrophilic Shewanella species, it has evolved specific genomic and proteomic adaptations for cold marine environments. These adaptations include decreased genome G+C content and reduced alanine, proline, and arginine content in their proteomes, which increases protein structural flexibility at lower temperatures (p-value <0.01) .

For ATP synthase function specifically, these cold adaptations likely manifest as structural modifications that maintain enzymatic activity and protein flexibility at lower temperatures. The ATP synthase complex must remain sufficiently flexible to permit the conformational changes necessary for proton translocation and ATP synthesis in cold environments. Additionally, S. halifaxensis has acquired numerous Na⁺-dependent nutrient transporters to utilize the high Na⁺ content in marine environments as an energy source , which may influence the ionic environment in which the ATP synthase operates.

What are the optimal storage and handling conditions for recombinant Shewanella halifaxensis ATP synthase subunit b (atpF)?

Optimal storage and handling of recombinant Shewanella halifaxensis ATP synthase subunit b requires careful attention to temperature and freeze-thaw cycles. Based on standard protocols for similar recombinant proteins:

• Long-term storage: Maintain at -20°C or preferably -80°C for extended preservation .

• Working solutions: Store aliquots at 4°C for up to one week to minimize protein degradation while maintaining accessibility for experimental work .

• Freeze-thaw management: Repeated freezing and thawing should be strictly avoided as it can lead to protein denaturation, aggregation, and loss of functional activity. Upon initial receipt, the protein should be divided into single-use aliquots before freezing .

• Buffer considerations: Typically, these proteins are stored in Tris-based buffers with 50% glycerol, optimized for protein stability. Similar proteins are stored in Tris/PBS-based buffers with 6% Trehalose at pH 8.0 .

• Reconstitution: Before use, centrifuge vials briefly to ensure all material is at the bottom. Reconstitute lyophilized protein in deionized sterile water to a concentration of 0.1-1.0 mg/mL, and consider adding glycerol (final concentration 5-50%) before aliquoting for long-term storage .

What experimental approaches can be used to study the functional role of ATP synthase subunit b in energy generation?

To investigate the functional role of ATP synthase subunit b in energy generation, researchers can employ several complementary experimental approaches:

What expression systems are most effective for producing recombinant Shewanella halifaxensis ATP synthase subunit b with optimal activity?

For the effective expression of recombinant Shewanella halifaxensis ATP synthase subunit b (atpF), several expression systems can be considered, each with specific advantages:

• E. coli-based expression systems:

  • Most commonly used for recombinant protein production due to rapid growth, high yields, and well-established protocols

  • For membrane proteins like ATP synthase subunits, E. coli strains optimized for membrane protein expression (C41, C43) can significantly improve yields

  • Expression vectors incorporating a His-tag facilitate subsequent purification

  • Consider using cold-shock promoters for the expression of psychrophilic proteins

• Cell-free protein synthesis:

  • Particularly valuable for membrane proteins that may be toxic to host cells

  • Allows direct incorporation into liposomes or nanodiscs

  • Provides greater control over the expression environment, including temperature and pH

• Temperature considerations:

  • Since S. halifaxensis is psychrophilic, lower expression temperatures (15-20°C) may yield properly folded, active protein

  • Extended expression times at lower temperatures can compensate for slower protein synthesis rates

• Codon optimization:

  • Adapting the atpF sequence to the codon usage of the expression host can improve translation efficiency

  • Particularly important when expressing psychrophilic genes in mesophilic expression hosts

• Fusion partners:

  • Solubility-enhancing tags (MBP, SUMO, Trx) can improve folding and stability

  • Cleavable tags allow tag removal after purification while maintaining a minimal tag for detection and purification

What purification challenges are specific to ATP synthase subunit b, and how can they be addressed?

Purification of ATP synthase subunit b presents several challenges due to its membrane association and structural properties. Researchers should consider the following strategies:

• Membrane protein solubilization:

  • Selection of appropriate detergents is crucial; mild detergents like n-dodecyl β-D-maltoside (DDM) or digitonin preserve structural integrity

  • Detergent screening should be performed to identify optimal solubilization conditions

  • Consider detergent-to-protein ratios carefully to avoid protein aggregation or denaturation

• Affinity chromatography optimization:

  • Immobilized metal affinity chromatography (IMAC) using Ni-NTA resins works effectively for His-tagged proteins

  • Low imidazole concentrations in wash buffers minimize non-specific binding

  • Elution with an imidazole gradient rather than step elution can improve purity

• Protein stability during purification:

  • Maintain cold temperatures (4°C) throughout purification

  • Include glycerol (10-20%) in buffers to enhance protein stability

  • Consider adding specific lipids that may be required for protein stability

• Aggregation prevention:

  • Size exclusion chromatography as a final purification step separates monomeric protein from aggregates

  • Dynamic light scattering can monitor aggregation state during purification optimization

• Protein activity assessment:

  • Verify functional activity after purification using ATPase activity assays

  • Reconstitution into liposomes can restore native-like environment for activity assays

How does the structure and function of ATP synthase subunit b differ between psychrophilic Shewanella halifaxensis and mesophilic Shewanella species?

The structural and functional differences in ATP synthase subunit b between psychrophilic S. halifaxensis and mesophilic Shewanella species reflect evolutionary adaptations to different temperature environments:

• Amino acid composition:

  • Psychrophilic S. halifaxensis likely displays reduced alanine, proline, and arginine content in its ATP synthase subunit b, consistent with the general trend observed in psychrophilic Shewanella proteomes

  • These compositional changes increase protein flexibility at lower temperatures, permitting necessary conformational changes during ATP synthesis

  • Increased hydrophilic residues on the protein surface may improve solvent interactions at lower temperatures

• Structural flexibility:

  • The psychrophilic ATP synthase subunit b likely exhibits increased flexibility, particularly in regions involved in subunit interactions

  • Reduced numbers of salt bridges and hydrogen bonds may contribute to this enhanced flexibility

  • Weaker protein-protein interactions may facilitate necessary movement during catalytic cycles at lower temperatures

• Thermal stability tradeoffs:

  • The increased flexibility that enables function at lower temperatures typically results in reduced thermal stability

  • This creates a characteristic shift in the temperature-activity profile toward lower temperatures

  • The activity maxima for psychrophilic ATP synthase complexes would occur at lower temperatures compared to mesophilic homologs

• Genomic adaptations:

  • Lower G+C content in the atpF gene from S. halifaxensis compared to mesophilic species reflects adaptation to cold environments

  • These genomic adaptations influence codon usage and ultimately protein composition

What is the evolutionary significance of ATP synthase structure in Shewanella halifaxensis compared to other marine bacteria?

The evolutionary path of ATP synthase in Shewanella halifaxensis reveals important adaptations to its specific ecological niche:

• Marine environment adaptations:

  • S. halifaxensis has undergone extensive gene exchange with deep-sea bacterial genomes, suggesting horizontal gene transfer played a significant role in its evolution

  • The recruitment of Na⁺-dependent nutrient transporters indicates adaptation to utilize high Na⁺ content in marine environments as an energy source

  • These adaptations may have influenced the ionic environment and energy dynamics in which ATP synthase operates

• Cold adaptation strategies:

  • The decreased genome G+C content and reduced alanine, proline, and arginine content in proteins represent convergent evolutionary strategies for cold adaptation

  • These adaptations suggest strong selective pressure for maintaining ATP synthase function at lower temperatures

  • Similar patterns observed across psychrophilic β-proteobacteria indicate convergent evolution in response to cold environments

• Functional conservation with structural adaptation:

  • Despite environmental adaptations, the core functional architecture of ATP synthase remains conserved

  • Evolutionary changes are primarily in amino acid composition rather than major structural rearrangements

  • This pattern exemplifies "structure conservation with sequence variation," a common evolutionary strategy for maintaining essential functions under diverse environmental conditions

• Ecological niche specialization:

  • S. halifaxensis was isolated from marine sediment and has specialized metabolic capabilities, including RDX degradation

  • The ATP synthase complex may have co-evolved with these specialized metabolic pathways to support energy requirements under specific environmental conditions

How can recombinant Shewanella halifaxensis ATP synthase subunit b be utilized in bioenergetic research?

Recombinant Shewanella halifaxensis ATP synthase subunit b offers valuable opportunities for advancing bioenergetic research:

• Cold-adapted bioenergetics models:

  • As a component from a psychrophilic organism, this protein provides an excellent model for studying energy generation mechanisms at low temperatures

  • Comparative studies with mesophilic counterparts can reveal temperature-dependent bioenergetic adaptations

  • Research using this protein can illuminate how proton motive force generation and utilization are maintained in cold environments

• Reconstituted systems:

  • Incorporation of purified recombinant atpF into liposomes or nanodiscs allows manipulation of the protein's environment

  • These reconstituted systems enable precise measurement of proton translocation and ATP synthesis under controlled conditions

  • Variables such as lipid composition, temperature, and pH can be systematically altered to assess their effects on function

• Structure-function relationship studies:

  • Site-directed mutagenesis of conserved residues can identify critical regions for function

  • Cross-linking studies with other ATP synthase subunits can map interaction surfaces

  • Single-molecule studies can reveal dynamic conformational changes during the catalytic cycle

• Biotechnological applications:

  • Cold-adapted ATP synthase components have potential applications in bioenergetic devices operating at low temperatures

  • Understanding the molecular basis of cold adaptation can inform protein engineering for improved functionality in biotechnological applications

  • Knowledge gained can contribute to the development of energy-harvesting systems based on biological principles

What methodological approaches are most effective for studying the role of ATP synthase in Shewanella halifaxensis' unique metabolic capabilities?

Investigating the connection between ATP synthase and S. halifaxensis' distinctive metabolic properties requires specialized methodological approaches:

What are common challenges encountered when working with recombinant ATP synthase subunits, and how can they be addressed?

Researchers frequently encounter several challenges when working with recombinant ATP synthase subunits. Here are effective strategies to address these issues:

How can researchers effectively analyze the interaction between ATP synthase subunit b and other components of the ATP synthase complex?

To effectively analyze the interactions between ATP synthase subunit b and other components of the complex, researchers can employ multiple complementary methodologies:

• In vitro reconstitution studies:

  • Purify individual ATP synthase components and reconstitute them in controlled environments

  • Monitor assembly using analytical ultracentrifugation or native PAGE

  • Measure functional parameters (ATP synthesis, proton translocation) in the reconstituted system

• Cross-linking coupled with mass spectrometry:

  • Chemical cross-linking can capture transient protein-protein interactions

  • Mass spectrometry analysis of cross-linked peptides identifies specific interaction sites

  • Zero-length cross-linkers versus spacer-containing cross-linkers provide different spatial information

• Cryo-electron microscopy:

  • High-resolution structural determination of the entire ATP synthase complex

  • Visualization of subunit b positioning within the intact complex

  • Comparison of structures under different functional states (e.g., ATP synthesis versus hydrolysis)

• Surface plasmon resonance (SPR) and microscale thermophoresis (MST):

  • Quantitative measurement of binding affinities between subunit b and other components

  • Determination of binding kinetics (association and dissociation rates)

  • Assessment of how mutations affect interaction strength

• Functional complementation assays:

  • In vivo assays where mutated versions of atpF are introduced into cells lacking the native gene

  • Assessment of ATP synthesis restoration provides functional evidence of successful interactions

  • Chimeric proteins combining domains from different species can identify critical interaction regions

What are promising future research directions for studying Shewanella halifaxensis ATP synthase in the context of cold adaptation?

Several promising research directions could significantly advance our understanding of S. halifaxensis ATP synthase in cold adaptation:

• Structural biology approaches:

  • High-resolution cryo-EM structures of the entire ATP synthase complex from S. halifaxensis at different temperatures

  • Comparative structural analysis with mesophilic homologs to identify cold-adaptive features

  • Molecular dynamics simulations to examine temperature-dependent conformational flexibility

• Synthetic biology applications:

  • Engineering chimeric ATP synthases combining cold-adapted components with mesophilic parts

  • Development of minimal ATP synthase models incorporating only essential subunits

  • Creation of hybrid energy-generating systems combining bacterial ATP synthases with artificial components

• Systems biology integration:

  • Global cellular responses to ATP synthase perturbation under different temperature regimes

  • Metabolic modeling to predict energy flux under varying environmental conditions

  • Integration of transcriptomic, proteomic, and metabolomic data to create comprehensive bioenergetic models

• Ecological and environmental applications:

  • Investigation of ATP synthase function in environmental samples containing Shewanella species

  • Study of ATP synthase activity in microbial communities adapting to temperature fluctuations

  • Development of biosensors based on ATP synthase components to monitor environmental conditions

How might understanding ATP synthase structure and function in Shewanella halifaxensis contribute to bioremediation applications?

The distinctive properties of ATP synthase in Shewanella halifaxensis offer significant potential for advancing bioremediation strategies:

• Energy generation during contaminant degradation:

  • S. halifaxensis has demonstrated ability to degrade RDX explosives, with increased cytochrome expression during this process

  • ATP synthase likely plays a crucial role in energy capture during these degradation pathways

  • Understanding how ATP synthase operates during contaminant metabolism could enhance engineered bioremediation systems

• Cold-environment bioremediation:

  • Many contaminated environments requiring remediation are in cold regions

  • S. halifaxensis ATP synthase adaptations for cold environments could inform development of more effective cold-climate bioremediation strategies

  • Potential for engineering other remediation-capable bacteria with cold-adapted ATP synthase components

• Coupling electron transport to contaminant reduction:

  • Shewanella species are known for their diverse respiratory capabilities

  • ATP synthase couples electron transport chain activity to energy capture

  • Understanding this coupling could lead to optimized electron flow during contaminant reduction processes

• Bioelectrochemical systems:

  • Shewanella species are utilized in microbial fuel cells and other bioelectrochemical systems

  • ATP synthase function is integral to energy harvesting in these applications

  • Insights from S. halifaxensis could improve efficiency of bioelectrochemical remediation technologies

• Metabolic engineering for enhanced bioremediation:

  • Modifying ATP synthase expression or structure could potentially enhance energy capture during remediation

  • Engineered strains with optimized ATP synthase could demonstrate improved contaminant degradation rates

  • Cross-species transfer of beneficial ATP synthase characteristics could expand the range of bioremediation organisms