Recombinant Shewanella halifaxensis ATP synthase subunit delta (atpH)

What is Shewanella halifaxensis and why is it of interest for ATP synthase research?

Shewanella halifaxensis is an obligately respiratory, denitrifying bacterium isolated from marine sediment (215m depth) in the Atlantic Ocean. It was identified as a novel species capable of degrading explosive compounds like hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) . The bacterium utilizes various carbon sources including peptone, yeast extract, amino acids, and several C2 and C3 acids . Its ATP synthase is of particular interest because it represents adaptation to marine environments, potentially exhibiting unique properties related to cold tolerance, salt resistance, and pressure adaptation. The study of S. halifaxensis ATP synthase can provide insights into bioenergetics of marine bacteria and extremophile adaptation mechanisms.

How does S. halifaxensis atpH structure-function relationship differ from other bacterial homologs?

The ATP synthase delta subunit (atpH) in S. halifaxensis likely exhibits adaptations specific to its marine environment, though direct structural comparisons are still emerging in research. As part of the F1F0-ATP synthase complex, the delta subunit serves as a connector between the catalytic F1 portion and the membrane-embedded F0 portion. Based on analyses of other Shewanella species, notable differences may include:

• Cold adaptation features: Higher flexibility in key regions to maintain function at lower temperatures

• Salt-tolerance mechanisms: Modified surface charge distribution to function in marine salt conditions

• Pressure-responsive elements: Structural adaptations allowing functionality at depth (215m)

Biochemical analysis of S. halifaxensis reveals it contains C14:0 (6%), iso-C15:0 (12%), C16:0 (20%), C16:1ω7 (37%), C18:1ω7 (7%), and C20:5ω3 (7%) as major membrane fatty acids, which may influence the lipid environment in which ATP synthase functions . Its respiratory quinones differ from terrestrial bacteria, with Q7 (28.1%) and MK-7 (60.9%) as dominant quinones , potentially affecting electron transport coupling to ATP synthesis.

What expression systems are optimal for producing functional recombinant S. halifaxensis atpH?

For recombinant production of S. halifaxensis atpH, several expression systems can be considered, each with distinct advantages:

Methodology for optimizing expression should include:

• Vector selection: pET series vectors with T7 promoter and appropriate fusion tags (His6, MBP, or SUMO)

• Induction parameters: IPTG concentration (0.1-1.0 mM), induction temperature and duration

• Media optimization: Marine-mimicking supplements may improve folding

• Co-expression with molecular chaperones to enhance proper folding

The choice of expression system should be guided by the specific experimental requirements, balancing yield with protein quality and functional authenticity.

What purification challenges are specific to S. halifaxensis atpH and how can they be overcome?

Purifying recombinant S. halifaxensis atpH presents several challenges related to its marine bacterial origin and structural characteristics:

• Aggregation issues: The protein may form aggregates during expression or purification

  • Solution: Include mild detergents (0.05% DDM or 0.5% CHAPS) in buffers

  • Add osmolytes (glycerol 10-20%, trehalose 50-100 mM) to stabilize native state

• Cold-sensitivity during purification

  • Solution: Maintain constant low temperature (4-10°C) throughout purification

  • Develop cold-adapted chromatography protocols with pre-chilled buffers

• Salt dependency for stability

  • Solution: Incorporate marine-relevant salt concentrations (200-300 mM NaCl)

  • Screen various salt types (KCl, MgCl₂) for optimal stability

• Heterogeneity in preparations

  • Solution: Employ additional polishing steps like ion exchange chromatography

  • Consider hydroxyapatite chromatography to separate conformational variants

A successful purification strategy often involves immobilized metal affinity chromatography (IMAC) followed by size exclusion chromatography in buffers optimized for marine protein stability (e.g., 50 mM Tris-HCl pH 7.5-8.0, 200 mM NaCl, 5% glycerol, 5 mM MgCl₂).

What techniques are most effective for analyzing the structure of S. halifaxensis atpH?

Multiple complementary techniques can provide comprehensive structural insights into S. halifaxensis atpH:

• X-ray crystallography

  • Requires extensive crystallization screening (500+ conditions)

  • Surface entropy reduction mutants may improve crystallization

  • Consider co-crystallization with binding partners to stabilize structure

• Cryo-electron microscopy

  • Particularly valuable for examining atpH in the context of complete ATP synthase

  • Single-particle analysis can reveal conformational states

  • Sample vitrification conditions need optimization for marine proteins

• Hydrogen-deuterium exchange mass spectrometry (HDX-MS)

  • Maps solvent accessibility and conformational dynamics

  • Can identify regions involved in subunit interactions

  • Provides insights into cold adaptation mechanisms through flexibility analysis

• Nuclear magnetic resonance (NMR) spectroscopy

  • Suitable if the isolated atpH is under 25 kDa

  • Provides dynamic information in solution state

  • Requires isotopic labeling (¹⁵N, ¹³C) during expression

• Small-angle X-ray scattering (SAXS)

  • Gives low-resolution envelope in solution

  • Useful for confirming quaternary structure and detecting conformational changes

  • Can be performed under various temperature and salt conditions to mimic native environment

A multi-technique approach combining high-resolution structural data with dynamic and solution-state information would provide the most comprehensive understanding of this protein's structure-function relationship.

How can researchers investigate conformational changes in S. halifaxensis atpH during ATP synthesis?

Investigating the dynamic conformational changes of atpH during ATP synthesis requires methodologies that capture protein dynamics:

• Single-molecule Förster resonance energy transfer (smFRET)

  • Strategic placement of fluorophore pairs at key positions in atpH

  • Real-time monitoring of distance changes during catalytic cycle

  • Can be performed under various substrate concentrations and environmental conditions

• Time-resolved electron paramagnetic resonance (EPR)

  • Site-directed spin labeling at strategic residues

  • Measures distances between labeled sites and their changes during function

  • Can detect subtle conformational shifts during catalysis

• Molecular dynamics (MD) simulations

  • All-atom simulations of atpH in membrane environment

  • Predict conformational responses to different nucleotide binding states

  • Model environmental effects (temperature, salt, pressure) on protein dynamics

• High-speed atomic force microscopy (HS-AFM)

  • Direct visualization of conformational changes at sub-second timescale

  • Can observe ATP synthase in reconstituted membrane systems

  • Correlates structural dynamics with functional states

• Integrated structural biology approach

  • Combine crystallographic/cryo-EM structures of different states

  • Use solution methods (SAXS, HDX-MS) to validate physiological relevance

  • Develop computational models connecting discrete structural states

These methods should be applied using reconstituted systems with controlled proton gradients to mimic the physiological function of ATP synthase. Comparison with mesophilic homologs would highlight adaptations specific to the marine environment of S. halifaxensis.

What assays best measure the functional activity of recombinant S. halifaxensis atpH?

Assessing the functional activity of recombinant atpH requires both isolated subunit analysis and studies within the ATP synthase complex:

• ATP synthase holoenzyme activity assays

  • ATP synthesis measurement using luciferin/luciferase luminescence

  • ATP hydrolysis measured by phosphate release (malachite green assay)

  • Proton pumping monitored with pH-sensitive fluorescent dyes

  • Activities should be measured across temperature range (4-30°C) relevant to marine environments

• atpH-specific functional analyses

  • Binding assays with other ATP synthase subunits (SPR, ITC, or MST)

  • Conformational change monitoring upon complex formation

  • Thermal stability shifts when bound to partner subunits

  • Effects of atpH variants on ATP synthase assembly and activity

• Comparative biochemical characterization

  • Side-by-side assays with atpH from mesophilic bacteria

  • Activity profiles across temperature, salt, and pressure gradients

  • Stability measurements under various environmental stresses

How does S. halifaxensis atpH contribute to the organism's energy metabolism in cold marine environments?

S. halifaxensis atpH likely plays a specialized role in energy metabolism adapted to cold marine conditions:

• Cold adaptation mechanisms

  • Increased flexibility in key regions to maintain catalytic efficiency at low temperatures

  • Modified interaction interfaces maintaining proper complex assembly in cold

  • Potentially unique regulatory properties responding to temperature fluctuations

• Connection to respiratory versatility

  • S. halifaxensis can utilize various electron acceptors including nitrate under anaerobic conditions

  • ATP synthase must couple efficiently to diverse respiratory chains

  • atpH may contain adaptations allowing efficient energy coupling across respiratory modes

• Marine-specific adaptations

  • Function in higher salt environments (seawater composition)

  • Response to hydrostatic pressure at depth (215m)

  • Potential interaction with unique membrane composition (containing high C20:5ω3)

• Energy efficiency strategies

  • Optimized ATP synthesis at lower energy investment

  • Maintenance of proton gradient under limiting conditions

  • Basal activity allowing survival in nutrient-limited environments

Research approaches should include in vivo studies measuring cellular ATP levels under various environmental conditions, comparative genomics with non-marine Shewanella species, and biochemical characterization of the ATP synthase complex under simulated marine conditions.

What mutagenesis strategies reveal critical functional residues in S. halifaxensis atpH?

Several mutagenesis approaches can identify key functional residues in S. halifaxensis atpH:

• Structure-guided site-directed mutagenesis

  • Target residues at predicted subunit interfaces

  • Modify putative cold-adapted regions (increased glycine/alanine content, reduced proline)

  • Alter surface-exposed charged residues potentially involved in salt adaptation

  • Create chimeric proteins with mesophilic homologs to identify critical regions

• Alanine-scanning mutagenesis

  • Systematic replacement of charged and hydrophobic clusters

  • Focus on regions with sequence divergence from mesophilic homologs

  • Target predicted flexible loops and hinges important for conformational changes

• Directed evolution approaches

  • Random mutagenesis libraries with screening for altered temperature sensitivity

  • Selection for variants with enhanced/reduced stability

  • Error-prone PCR followed by functional selection

• Analytical methods for mutant characterization

  • Thermal shift assays to quantify stability changes

  • Binding assays to measure interaction with partner subunits

  • Activity assays in reconstituted systems

  • Structural analysis of successful mutants

These approaches should be combined with computational analysis of sequence conservation and evolutionary covariance to identify potentially important residues before experimental validation.

How can CRISPR-Cas9 gene editing be applied to study atpH function in the native S. halifaxensis?

CRISPR-Cas9 technology offers powerful approaches for studying atpH in its native context:

• Genetic modification strategies

  • Knockout/knockdown studies to assess essentiality

  • Precise point mutations to test specific hypotheses

  • Insertion of reporter tags for localization and expression studies

  • Promoter modifications to alter expression levels

• Methodological considerations for Shewanella

  • Optimization of transformation protocols for marine bacteria

  • Selection of appropriate PAM sites in AT-rich genomic regions

  • Development of delivery systems effective in S. halifaxensis

  • Screening methods compatible with growth requirements

• Experimental designs

  • Creation of conditional mutants if atpH is essential

  • Complementation studies with variant atpH genes

  • Phenotypic characterization under various environmental conditions

  • Comparative growth studies at different temperatures, salinities, and pressures

• Integration with other approaches

  • Transcriptomic analysis of edited strains

  • Metabolomic profiling to assess bioenergetic impacts

  • Proteomic studies to identify compensatory mechanisms

This approach allows examination of atpH function without overexpression artifacts and within its native genomic context, providing physiologically relevant insights into its role in cellular bioenergetics.

What is the relationship between ATP synthase and extracellular electron transfer in Shewanella species?

Shewanella species are known for their remarkable ability to perform extracellular electron transfer (EET), and ATP synthase plays an important role in this process:

• Bioenergetic coupling mechanisms

  • ATP synthesis driven by proton motive force generated during EET

  • Potential reverse electron flow under certain conditions

  • Energy conservation strategies during anaerobic respiration

• Evidence from other Shewanella species

  • Transcriptional analysis of S. oneidensis MR-1 showed differential expression of ATP synthase genes during electrode respiration

  • ATP synthase activity correlates with metal reduction rates

  • Metabolic modeling suggests ATP synthase is critical for energy conservation during EET

• Unique features in S. halifaxensis

  • Adaptation to marine environment may affect EET-ATP synthesis coupling

  • Cold adaptation features might enable efficient energy harvesting at lower temperatures

  • Marine-specific electron acceptors may drive unique respiratory chains

• Research methodologies

  • Membrane potential measurements during EET using fluorescent probes

  • Direct measurement of ATP production with various electron acceptors

  • Correlation of ATP synthase activity with metal reduction rates

  • Genetic studies manipulating atpH expression and monitoring effects on EET

The study of this relationship provides insights into how bacteria optimize energy harvesting from diverse electron acceptors in challenging environments and has implications for biotechnological applications in microbial fuel cells and bioremediation.

How does atpH contribute to the bioenergetics of explosive compound degradation in S. halifaxensis?

S. halifaxensis was initially isolated for its ability to degrade explosive compounds like RDX , and ATP synthase likely plays a critical role in this process:

• Energetic requirements of explosive degradation

  • ATP demands for enzyme expression and cellular maintenance during degradation

  • Energy conservation mechanisms during anaerobic RDX metabolism

  • Potential stress responses requiring ATP during exposure to explosives

• Specialized adaptations of atpH

  • Potential unique regulatory features responding to explosive compounds

  • Efficiency adaptations for energy harvesting during degradation

  • Structural features maintaining function under chemical stress

• Integration with respiratory chains

  • Coupling of ATP synthesis to electron transport during explosive reduction

  • Alternative respiratory pathways activated during explosive compound metabolism

  • Proton gradient maintenance under degradation conditions

• Research approaches

  • Comparative proteomics of ATP synthase components during growth with/without explosives

  • Measurement of cellular ATP levels during explosive degradation

  • Genetic manipulation of atpH and effects on degradation capacity

  • In vitro reconstitution of ATP synthase activity with degradation intermediates

Understanding this relationship has significant implications for environmental bioremediation applications, potentially allowing optimization of S. halifaxensis for enhanced degradation of explosive contaminants in marine environments.

How can structural information about S. halifaxensis atpH inform biomimetic energy systems?

Structural insights into S. halifaxensis atpH can inspire biomimetic approaches for energy technologies:

• Nanoscale rotary motors

  • Design principles from cold-adapted ATP synthase can inform molecular machine engineering

  • Efficiency mechanisms from S. halifaxensis may inspire low-temperature nanomotors

  • Biomimetic rotary devices with improved salt tolerance for marine applications

• Biosensor development

  • atpH conformational changes as sensing elements for environmental monitoring

  • Detection systems for marine pollutants based on ATP synthase activity

  • Energy-generating biosensors for remote deployment

• Cold-adapted bioenergetic systems

  • Artificial photosynthetic systems incorporating design elements from marine ATP synthases

  • Energy conversion systems operating efficiently at low temperatures

  • Biomimetic membranes with optimized proton conductance

• Research methodology

  • High-resolution structural determination under various conditions

  • Computational modeling of energy transduction mechanisms

  • Rational design of peptides mimicking functional domains

  • Reconstitution in artificial membrane systems to test biomimetic designs

The marine origin of S. halifaxensis atpH provides unique design principles for energy technologies operating in challenging environments, including cold, saline, or high-pressure conditions.

What insights can comparative studies between S. halifaxensis atpH and other extremophilic ATP synthases provide?

Comparative analyses between S. halifaxensis atpH and other extremophilic ATP synthases can reveal fundamental adaptations to environmental challenges:

• Adaptation mechanisms across extremes

  • Cold adaptation (psychrophiles) vs. heat adaptation (thermophiles)

  • Pressure adaptation (barophiles) vs. atmospheric pressure adaptation

  • Salt tolerance mechanisms across halophiles and marine organisms

• Conserved vs. variable features

  • Core functional elements preserved across extremophiles

  • Variable regions reflecting specific environmental adaptations

  • Convergent evolution in distantly related extremophiles

• Structural basis of adaptations

  • Surface charge distribution patterns across extremophiles

  • Flexibility/rigidity balance in relation to environmental conditions

  • Subunit interaction interfaces and their environmental modulation

• Research approaches

  • Phylogenetic analysis of atpH across extremophiles

  • Structural comparison of homologs from different extreme environments

  • Chimeric protein construction and functional testing

  • Molecular dynamics simulations under various extreme conditions

Such comparative studies provide fundamental insights into protein adaptation mechanisms and may reveal design principles for engineering proteins with enhanced stability and function under challenging conditions.

How can researchers overcome difficulties in reconstituting functional S. halifaxensis ATP synthase complexes?

Reconstitution of functional ATP synthase complexes presents several challenges that require systematic approaches:

• Component expression and purification

  • Develop co-expression systems for multiple subunits

  • Optimize detergent extraction to maintain native interactions

  • Employ mild purification conditions preserving complex integrity

  • Consider native isolation methods for reference comparisons

• Membrane environment reconstitution

  • Match lipid composition to S. halifaxensis membranes (high C16:1ω7 and C20:5ω3 content)

  • Test various proteoliposome preparation methods

  • Explore nanodiscs with different scaffold proteins

  • Optimize protein-to-lipid ratios for functional reconstitution

• Functional validation methods

  • Develop sensitive ATP synthesis assays for small-scale reconstitutions

  • Monitor proton pumping with pH-sensitive fluorescent dyes

  • Measure rotation directly using single-molecule techniques

  • Assess complex integrity through native gel electrophoresis

• Environmental parameter optimization

  • Test temperature ranges relevant to marine environments (4-20°C)

  • Incorporate appropriate salt concentrations based on natural habitat

  • Consider pressure effects for deep-sea bacteria

Successful reconstitution typically requires iterative optimization, beginning with simplified subcomplexes before attempting full ATP synthase reconstitution.

What approaches help differentiate the specific role of atpH from other ATP synthase subunits?

Isolating the specific contribution of atpH requires sophisticated experimental strategies:

• Selective disruption methods

  • Strategic mutagenesis targeting atpH interaction interfaces

  • Antibodies or nanobodies specifically binding atpH

  • Competitive peptides mimicking atpH interaction surfaces

  • Controlled proteolysis targeting accessible regions of atpH

• Domain swap experiments

  • Replace S. halifaxensis atpH with homologs from different species

  • Create chimeric proteins with domains from different organisms

  • Systematically exchange interface regions to map functional boundaries

  • Test hybrid complexes under various environmental conditions

• Biophysical characterization approaches

  • FRET sensors placed at strategic positions to monitor atpH movement

  • Cross-linking studies to capture transient interaction states

  • Hydrogen-deuterium exchange to map conformational changes

  • Single-molecule analysis of rotation with/without modified atpH

• In silico approaches

  • Molecular dynamics simulations with modified atpH structures

  • Normal mode analysis to identify atpH contributions to global motions

  • Energy landscape calculation for different atpH configurations

These approaches collectively provide a comprehensive understanding of atpH's specific contributions to ATP synthase structure, stability, and function in the unique context of S. halifaxensis.