Recombinant Staphylococcus carnosus ATP synthase subunit a (atpB)

How is recombinant S. carnosus atpB typically expressed and purified?

Recombinant S. carnosus atpB is typically expressed in E. coli expression systems with an N-terminal His-tag to facilitate purification . The standard expression and purification protocol follows these methodological steps:

• Gene synthesis or PCR amplification of the atpB coding sequence

• Cloning into an expression vector containing an N-terminal His-tag

• Transformation into appropriate E. coli strains optimized for membrane protein expression

• Culture growth and protein expression induction

• Cell harvest and membrane isolation

• Membrane solubilization using appropriate detergents

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

• Optional additional purification steps (size exclusion chromatography, ion exchange)

• Concentration and storage in stabilizing buffer conditions

The purified protein is typically verified for purity using SDS-PAGE, with expected purity greater than 90% . Being a membrane protein, special attention must be paid to maintaining proper detergent concentrations throughout the purification process to prevent aggregation.

What are the recommended storage conditions for recombinant atpB protein?

Based on established protocols, the following storage conditions are recommended for maintaining the stability and functionality of recombinant S. carnosus atpB protein:

• Store the lyophilized powder at -20°C to -80°C upon receipt

• Reconstitute in deionized sterile water to a concentration of 0.1-1.0 mg/mL

• Add glycerol to a final concentration of 50% for long-term storage (this prevents ice crystal formation that can damage protein structure)

• Store in Tris/PBS-based buffer with 6% trehalose at pH 8.0

• Aliquot to avoid repeated freeze-thaw cycles

• For working solutions, store at 4°C for up to one week

It is critical to note that repeated freezing and thawing should be avoided as it can lead to protein denaturation, aggregation, and loss of functional activity. Researchers should centrifuge the vial briefly before opening to bring contents to the bottom of the tube .

What is the role of ATP synthase in Staphylococcus species?

ATP synthase in Staphylococcus species serves several essential functions beyond its canonical role in energy production:

• Energy Metabolism: The primary function is synthesizing ATP through oxidative phosphorylation, utilizing the proton motive force across the membrane.

• Biofilm Formation: In S. aureus, ATP synthase components significantly impact biofilm architecture and stability. Mutations in ATP synthase genes result in more diffuse biofilm structures that are more permissive to immune cell infiltration .

• Immune Response Modulation: ATP synthase influences host-pathogen interactions by affecting bacterial toxin and protease production. Disruption of ATP synthase function (specifically in the alpha subunit) results in increased production of proinflammatory cytokines including IL-12p70, TNF-α, and IL-6 by immune cells .

• Bacterial Persistence: Functional ATP synthase contributes to bacterial persistence in biofilm-associated infections by modulating both bacterial metabolism and host immune responses .

While much of this research has been conducted in S. aureus rather than S. carnosus specifically, the high conservation of ATP synthase across species suggests similar functional roles likely exist in S. carnosus.

How does ATP synthase structure-function relationship influence bacterial persistence in Staphylococcus infections?

The relationship between ATP synthase structure-function and bacterial persistence in Staphylococcus infections is complex and multifaceted:

• Biofilm Architecture: Studies in S. aureus demonstrate that ATP synthase mutations (specifically in the alpha subunit, atpA) result in altered biofilm architecture characterized by a more diffuse structure. This architectural change increases susceptibility to immune cell infiltration and antimicrobial agents .

• Metabolic Adaptation: ATP synthase facilitates adaptation to the unique metabolic environment within biofilms, where oxygen and nutrient gradients exist. Specific structural features of ATP synthase components like atpB allow for fine-tuning of energy production under these challenging conditions.

• Immunomodulatory Effects: The structural components of ATP synthase influence toxin and protease production profiles, which directly impact host immune responses. When ATP synthase function is compromised, bacteria elicit stronger proinflammatory cytokine responses (IL-12p70, TNF-α, IL-6) from immune cells like macrophages and myeloid-derived suppressor cells (MDSCs) .

• Autolysis Regulation: ATP synthase function appears to influence cell lysis processes, as the enhanced inflammatory response elicited by ATP synthase mutants is cell lysis-dependent .

These findings suggest that structural features of ATP synthase components, potentially including atpB, have evolved not only for optimal energy production but also to support pathogenesis and persistence through immunomodulatory functions.

What methodological approaches are most effective for analyzing atpB interactions with other ATP synthase components?

Analyzing interactions between atpB and other ATP synthase components requires sophisticated methodological approaches:

• Cross-linking Mass Spectrometry:

  • Chemical cross-linking of intact ATP synthase complex

  • Digestion and LC-MS/MS analysis

  • Identification of cross-linked peptides to map interaction interfaces

• Förster Resonance Energy Transfer (FRET):

  • Site-specific labeling of atpB and potential interaction partners

  • Measurement of energy transfer efficiency

  • Determination of proximity and orientation relationships

• Co-immunoprecipitation with Targeted Mutations:

  • Systematic mutation of potential interaction surfaces

  • Co-IP using antibodies against partner subunits

  • Western blot analysis to quantify interaction strength

• Surface Plasmon Resonance (SPR):

  • Immobilization of purified atpB on sensor chips

  • Flowing potential interaction partners over the surface

  • Real-time measurement of association/dissociation kinetics

• Hydrogen-Deuterium Exchange Mass Spectrometry (HDX-MS):

  • Exposure of individual proteins and complexes to deuterium

  • Analysis of differential deuterium uptake

  • Identification of protected regions indicating interaction surfaces

These approaches can be complemented with computational methods such as molecular docking and molecular dynamics simulations to develop comprehensive interaction models.

How can recombinant S. carnosus atpB be effectively reconstituted into liposomes for functional studies?

Reconstitution of recombinant S. carnosus atpB into liposomes is essential for functional studies and requires careful methodological consideration:

• Preparation of Proteoliposomes:

  Step	Method	Critical Parameters
  Lipid Selection	Mixture of phosphatidylcholine, phosphatidylethanolamine (70:30)	Lipid composition affects protein insertion and activity
  Liposome Formation	Thin film hydration followed by extrusion	Uniform size distribution (100-200 nm optimal)
  Protein Incorporation	Detergent-mediated incorporation	Protein:lipid ratio (1:100 to 1:1000)
  Detergent Removal	Bio-Beads adsorption or dialysis	Rate of removal affects insertion efficiency

• Quality Control Assessment:

  • Freeze-fracture electron microscopy to visualize protein insertion

  • Dynamic light scattering to confirm vesicle size distribution

  • Sucrose density gradients to separate proteoliposomes from empty liposomes

  • Protein quantification to determine reconstitution efficiency

• Functional Characterization:

  • Proton translocation assays using pH-sensitive fluorescent dyes (ACMA or pyranine)

  • Membrane potential measurements using voltage-sensitive dyes

  • ATP synthesis activity when co-reconstituted with other ATP synthase components

  • Patch-clamp electrophysiology for single-channel recordings

• Orientation Analysis:

  • Protease accessibility assays to determine protein orientation

  • Antibody labeling of accessible epitopes

  • Functional assays with sidedness-specific inhibitors

This reconstitution approach provides a controlled membrane environment that mimics native conditions, allowing for detailed functional characterization of atpB's proton translocation activity.

What experimental evidence links ATP synthase function to biofilm formation in Staphylococcus species?

Recent experimental evidence has established significant connections between ATP synthase function and biofilm formation in Staphylococcus species:

• Genetic Evidence:

  • Transposon mutagenesis identified atpA (ATP synthase alpha subunit) as a factor influencing biofilm formation

  • ATP synthase mutants show altered growth kinetics in both planktonic and biofilm conditions

• Structural Analysis:

  • Confocal laser scanning microscopy demonstrates that ATP synthase mutants form biofilms with diffuse architecture that permits increased leukocyte infiltration

  • This structural change likely contributes to increased susceptibility to host immune clearance

• Immunological Impact:

  • Co-culture experiments show that ATP synthase-deficient biofilms elicit significantly increased production of proinflammatory cytokines (IL-12p70, TNF-α, IL-6) from immune cells

  • This enhanced inflammatory response is associated with improved biofilm clearance

• Mechanism Analysis:

  • The inflammatory response triggered by ATP synthase mutants is cell lysis-dependent

  • ATP synthase mutants show reduced production of toxins and proteases that normally suppress immune responses

  • These findings suggest ATP synthase influences virulence factor production

• In Vivo Confirmation:

  • In a mouse model of prosthetic joint infection, ATP synthase mutants showed decreased ability to establish persistent infection

  • Infections with ATP synthase mutants had decreased myeloid-derived suppressor cells and increased monocyte/macrophage infiltrates

While these studies focused primarily on the alpha subunit (atpA), the integral nature of ATP synthase function suggests that atpB likely plays a similarly important role in these processes.

What expression systems are optimal for producing functional recombinant S. carnosus atpB?

Selecting the optimal expression system for S. carnosus atpB requires balancing protein yield, functionality, and experimental feasibility:

• E. coli Expression Systems:

  • Advantages: Well-established protocols, high yields, simple culturing

  • Specialized strains: C41(DE3) and C43(DE3) designed for membrane proteins

  • Optimal vectors: pET series with T7 promoters for controlled expression

  • Expression conditions: Induction at lower temperatures (16-18°C) with reduced IPTG concentrations (0.1-0.5 mM)

• Yeast Expression Systems:

  • Advantages: Eukaryotic folding machinery, post-translational modifications

  • Pichia pastoris: Particularly suitable for membrane proteins with high biomass yield

  • Expression strategy: Methanol-inducible promoters with careful induction protocols

  • Processing: Proper signal peptide selection critical for membrane targeting

• Cell-Free Expression Systems:

  • Advantages: Avoids toxicity issues, direct incorporation into nanodiscs or liposomes

  • Formats: E. coli extracts supplemented with lipids or detergents

  • Optimization: Requires careful adjustment of reaction components

  • Scale: Smaller scale but higher success rate for difficult membrane proteins

• Insect Cell Expression:

  • Advantages: Superior folding for complex membrane proteins

  • Baculovirus system: High expression levels with proper membrane targeting

  • Timeline: Longer production cycle but potentially better functionality

  • Purification: Similar downstream processing as other systems

For S. carnosus atpB specifically, E. coli expression with an N-terminal His-tag has been successfully implemented , but researchers should consider alternative systems if functional studies indicate improper folding or reduced activity.

What purification strategies maximize yield and purity of functional recombinant atpB?

Purification of membrane proteins like atpB requires specialized approaches to maintain structural integrity while achieving high purity:

• Membrane Preparation and Solubilization:

  • Gentle cell lysis (French press or sonication with protease inhibitors)

  • Membrane isolation by ultracentrifugation

  • Screening of detergents (DDM, LMNG, digitonin) for optimal solubilization

  • Critical parameters: detergent:protein ratio, temperature, incubation time

• Affinity Chromatography:

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

  • Careful optimization of imidazole concentration in wash and elution buffers

  • Addition of glycerol (10%) and detergent (above CMC) in all buffers

  • Consideration of on-column detergent exchange if needed

• Secondary Purification Steps:

  • Size exclusion chromatography to remove aggregates and improve homogeneity

  • Ion exchange chromatography for separating oligomeric states

  • Affinity purification with ATP synthase-specific ligands

• Quality Control Assessments:

  • SDS-PAGE analysis with target purity >90%

  • Western blotting for identity confirmation

  • Mass spectrometry for sequence verification

  • Dynamic light scattering for aggregation analysis

• Stabilization Strategies:

  • Addition of lipids to maintain native-like environment

  • Inclusion of 6% trehalose as stabilizing agent

  • Buffer optimization (typically Tris/PBS-based at pH 8.0)

  • Immediate aliquoting and flash-freezing to prevent degradation

This systematic approach maximizes both yield and functional integrity of the purified atpB protein, providing material suitable for downstream structural and functional studies.

What methods are most effective for analyzing the membrane topology of S. carnosus atpB?

Determining the membrane topology of integral membrane proteins like S. carnosus atpB requires multiple complementary approaches:

• Computational Prediction Methods:

  • Hydropathy analysis using multiple algorithms (TMHMM, HMMTOP, Phobius)

  • Consensus topology mapping from multiple prediction tools

  • Comparative analysis with homologous proteins of known structure

• Biochemical Mapping Techniques:

  • Substituted cysteine accessibility method (SCAM)

    • Sequential replacement of residues with cysteines

    • Treatment with membrane-impermeable sulfhydryl reagents

    • Identification of protected vs. accessible positions

  • Limited proteolysis

    • Digestion of intact membrane vesicles or proteoliposomes

    • Mass spectrometry analysis of protected fragments

    • Mapping of cleavage sites to protein sequence

• Fluorescence-Based Methods:

  • Site-directed fluorescence labeling

    • Introduction of fluorescent probes at specific positions

    • Quenching studies with water-soluble and membrane-soluble quenchers

    • Measurement of fluorescence lifetimes and accessibility

  • FRET analysis

    • Dual labeling with donor/acceptor fluorophores

    • Distance measurements between labeled positions

    • Triangulation to determine relative positions in membrane

• Structural Biology Approaches:

  • Cryo-electron microscopy of reconstituted complexes

  • NMR spectroscopy of isotopically labeled protein

  • X-ray crystallography (challenging for membrane proteins)

• Genetic Fusion Approaches:

  • Reporter fusion strategy

    • Fusion of reporters (PhoA, GFP, LacZ) at different positions

    • Activity/fluorescence indicates cellular localization

    • Systematic analysis to map topology

These methods together provide a comprehensive picture of how atpB traverses the membrane, identifying transmembrane segments, loop regions, and their orientation relative to the membrane.

What functional assays can confirm proper folding and activity of recombinant S. carnosus atpB?

Verifying the proper folding and functional activity of recombinant S. carnosus atpB requires specialized assays that address both structural integrity and functional capacity:

• Structural Integrity Assays:

  • Circular Dichroism (CD) Spectroscopy

    • Assessment of secondary structure content (alpha-helical content expected to be high)

    • Thermal stability measurements

    • Comparison with predicted structural characteristics

  • Intrinsic Tryptophan Fluorescence

    • Measurement of emission spectra to assess tertiary structure

    • Quenching studies to determine accessibility of tryptophan residues

    • Denaturation curves to evaluate stability

  • Limited Proteolysis Profiles

    • Digestion patterns compared to correctly folded standards

    • Mass spectrometry analysis of fragments

    • Resistance to proteolysis indicates compact folding

• Functional Activity Assays:

  • Proton Translocation Measurements

    • Reconstitution into liposomes with pH-sensitive dyes (ACMA, pyranine)

    • Measurement of pH gradient formation/dissipation

    • Effect of specific inhibitors (DCCD, oligomycin)

  • ATP Synthesis Coupling (with complete ATP synthase)

    • Co-reconstitution with other ATP synthase subunits

    • Measurement of ATP production upon establishment of proton gradient

    • Comparison with native enzyme activity

  • Binding Assays with Partner Subunits

    • Surface plasmon resonance with other F0 components

    • Co-immunoprecipitation studies

    • Chemical cross-linking followed by mass spectrometry

• Comparative Benchmarking:

  • Comparison with wild-type protein characteristics

  • Activity relative to homologous proteins from other species

  • Structure-function relationships based on known ATP synthase mechanisms

These assays collectively provide a comprehensive assessment of whether the recombinant atpB protein has folded correctly and maintains its functional capabilities, which is essential before proceeding to detailed mechanistic or structural studies.

How can S. carnosus surface display systems be utilized for expressing functional atpB derivatives?

S. carnosus offers significant potential as a platform for surface display of atpB derivatives with various research and biotechnological applications:

• Surface Display Expression System Design:

  • Vector Construction: Fusion constructs can be created utilizing the S. carnosus surface display system, which typically employs a signal peptide (e.g., from S. hyicus lipase), the target protein, and cell wall anchoring domains

  • Membrane Topology Preservation: Careful design of fusion points to maintain critical transmembrane domains and functional regions

  • Expression Control: Utilization of promoters suitable for controlled expression in S. carnosus

• Methodological Approaches for Verification:

  • Immunological Detection: Surface-displayed proteins can be verified using antibodies against atpB or incorporated epitope tags

  • Functional Assays: Colorimetric assays can be developed to assess functionality of displayed proteins

  • Electron Microscopy: Immunogold labeling allows visualization of surface-displayed proteins

• Research Applications:

  • Structure-Function Analysis: Systematic exposure of different atpB domains for accessibility studies

  • Protein Engineering: Generation of variant libraries with improved properties

  • Interaction Studies: Analysis of binding with other ATP synthase components in a controlled environment

• Biotechnological Applications:

  • Vaccine Development: Surface display of atpB epitopes for immunization against pathogenic Staphylococcus species

  • Biosensor Development: Creation of whole-cell sensors for ATP synthesis inhibitors

  • Biocatalysis: Engineering of modified atpB variants with novel functions

The advantages of using S. carnosus as an expression host include its non-pathogenic nature, absence of protein A and exotoxins, and robust growth characteristics . These features make it particularly suitable for applications requiring safe handling and stable expression.

What potential exists for targeting ATP synthase in antimicrobial development against Staphylococcus species?

ATP synthase represents a promising target for novel antimicrobial development against Staphylococcus species, with several strategic approaches:

• Rationale for Targeting ATP Synthase:

  • Essential Function: ATP synthase is critical for energy metabolism and bacterial survival

  • Biofilm Connection: ATP synthase influences biofilm formation and persistence

  • Immune Modulation: ATP synthase affects host-pathogen interactions

  • Structural Differences: Bacterial ATP synthases differ from mammalian counterparts

• Inhibition Strategies:

  • Small Molecule Inhibitors:

    • Targeting the proton channel formed by a-subunit (atpB)

    • Disrupting rotational coupling between F0 and F1 sectors

    • Interfering with assembly of the complex

  • Peptide-Based Inhibitors:

    • Designed based on interface regions between subunits

    • Mimicking natural protein-protein interaction surfaces

    • Enhanced delivery using cell-penetrating peptides

  • Immunological Approaches:

    • Antibodies targeting exposed epitopes of ATP synthase

    • Vaccines based on conserved regions of ATP synthase components

    • Immunomodulators to enhance host response against ATP synthase mutants

• Therapeutic Potential:

  • Biofilm Disruption: Compounds that mimic ATP synthase mutation effects could increase biofilm susceptibility to immune clearance

  • Combination Therapy: ATP synthase inhibitors could potentiate existing antibiotics

  • Anti-virulence Strategy: Modulating ATP synthase to reduce virulence factor production without directly killing bacteria

• Challenges and Considerations:

  • Selectivity: Ensuring specific targeting of bacterial over human ATP synthase

  • Delivery: Getting inhibitors across bacterial cell envelope

  • Resistance Development: Understanding potential resistance mechanisms

The connection between ATP synthase function and biofilm persistence makes this target particularly promising for addressing biofilm-associated infections, which are notoriously difficult to treat with conventional antibiotics.

How does the structure-function relationship of atpB influence bacterial adaptation to environmental stresses?

The structure-function relationship of atpB plays a critical role in bacterial adaptation to various environmental stresses:

• Metabolic Adaptation Mechanisms:

  • Proton Gradient Regulation:

    • atpB's proton channel structure allows modulation of proton flow

    • Structural features permit adaptation to varying pH conditions

    • Conformational changes can adjust ATP synthesis rates to match metabolic demands

  • Energy Conservation:

    • Structural elements of atpB contribute to preventing proton leakage

    • Maintaining membrane integrity during energy limitation

    • Specialized domains may allow for reversible ATP synthase activity (ATP hydrolysis)

• Response to Environmental Challenges:

  • Acid Stress:

    • atpB structure influences bacterial survival in acidic environments

    • Specific residues in transmembrane domains may buffer proton flow under acidic conditions

    • Conformational adaptations can protect against excessive proton influx

  • Oxidative Stress:

    • Structural features may provide resistance to oxidative damage

    • Specific amino acid residues serve as oxidation targets or protectors

    • Interaction with other membrane components to maintain function during stress

  • Antimicrobial Exposure:

    • Conformational changes in response to membrane-active compounds

    • Structural adaptations that maintain ATP synthesis during antibiotic challenge

    • Potential role in energy-dependent resistance mechanisms

• Biofilm-Specific Adaptations:

  • Structural elements of atpB likely contribute to the specialized energy metabolism within biofilms

  • Potential conformational states optimized for the low-oxygen environment of biofilm interiors

  • Structural interactions that influence biofilm matrix production and architecture

• Evolution of Structural Variations:

  • Comparative analysis across Staphylococcus species reveals evolutionary adaptations

  • Species-specific structural features likely reflect ecological niches

  • Conserved domains indicate fundamental functional requirements

Understanding these structure-function relationships provides insights into bacterial persistence mechanisms and may reveal new approaches for controlling Staphylococcal infections.