Recombinant Nocardia farcinica ATP synthase subunit b (atpF)

What is the significance of Nocardia farcinica ATP synthase subunit b in bacterial physiology and pathogenicity?

ATP synthase subunit b (atpF) is a critical component of the F0F1 ATP synthase complex in Nocardia farcinica, an opportunistic pathogen that causes nocardiosis in humans and animals. The ATP synthase complex catalyzes the formation of ATP from ADP and inorganic phosphate, serving as one of the most crucial protein complexes in energy metabolism .

In N. farcinica, this protein consists of 186 amino acids with the sequence: MYEYSVLAAESGEDVNPLIPATYDIVWSVVCVAIIAVVFYKYVIPRLTKVLNERADKIEGGIAKAEAAQAEAQQTLEQYQQQLADARLEAARIREDARTQGQQILAQMRAEAQAESDRIVAAGHAQLEAQRQQILTELRSEVGRTAVDLAEKIIGQSVSDEAKQAASIERFLSELDSSDA GIGVGR .

The atpF gene (designated as NFA_10610 in the N. farcinica IFM 10152 genome) produces a protein that functions as part of the membrane-embedded F0 sector of ATP synthase . This protein's role in energy metabolism makes it particularly interesting when studying this pathogen's survival mechanisms both in environmental and host conditions.

What are the optimal methods for recombinant expression of Nocardia farcinica atpF?

The recombinant expression of N. farcinica atpF has been successfully achieved using the following methodological approach:

Expression System Selection:
E. coli is the predominant expression system for producing recombinant N. farcinica atpF protein . This system offers advantages including rapid growth, high protein yields, and well-established protocols.

Expression Construct Design:

• The full-length atpF gene (encoding amino acids 1-186) should be cloned into a suitable expression vector

• Addition of purification tags is recommended - typically an N-terminal His-tag or His-SUMO tag

• The construct should include appropriate promoters (T7 is commonly used) and selection markers

Optimization Parameters:

• Induction conditions: IPTG concentration (typically 0.1-1.0 mM), temperature (often lowered to 16-25°C for membrane proteins), and duration (4-16 hours)

• Growth medium: Rich media (like LB) or minimal media depending on downstream applications

• Codon optimization may be necessary due to the high G+C content (70.8%) of N. farcinica

For extraction of the protein, careful lysis buffer selection is critical since atpF is a membrane protein component. Buffers containing mild detergents such as n-dodecyl-β-D-maltoside (DDM) or Triton X-100 have proven effective for similar membrane proteins.

How can researchers assess the purity and activity of recombinant atpF after purification?

Multiple complementary methods should be employed to thoroughly assess both purity and activity:

Purity Assessment Methods:

• SDS-PAGE: The purity of recombinant atpF can be determined using SDS-PAGE, with expected purity levels of ≥85-90% . The theoretical molecular weight of atpF is approximately 20.3 kDa .

• Western Blot: Using antibodies against the protein itself or the purification tag to confirm identity.

• Mass Spectrometry: For definitive identification and purity assessment. As demonstrated in related ATP synthase purification protocols, MS can identify all components and contaminants .

• Blue-Native PAGE: Particularly useful if studying the protein as part of the complete ATP synthase complex .

Activity Assessment Methods:
While direct activity assays for isolated atpF are challenging since it functions as part of a complex, these approaches can be valuable:

• Reconstitution Experiments: Incorporating purified atpF into liposomes with other ATP synthase components.

• ATP Hydrolysis Assay: If studying the complete ATP synthase complex containing atpF, an ATP hydrolysis assay can be conducted as described in related protocols .

• Binding Studies: Assessing interaction with other ATP synthase subunits using techniques such as surface plasmon resonance or pull-down assays.

What experimental designs are most effective for studying atpF function?

When investigating atpF function, several experimental design approaches can be employed:

Basic Experimental Designs:

• One Factor at a Time (OFAT) Approach:

  • Suitable for preliminary investigations

  • Examines the effect of single variables (e.g., pH, temperature, ion concentration) on atpF function

  • Less efficient but simpler to implement and analyze

• Full Factorial Design:

  • Provides comprehensive analysis of multiple factors and their interactions

  • Useful for initial characterization of atpF functional parameters

  • Requires substantial experimental resources

Advanced Experimental Designs:

• Fractional Factorial Design:

  • More efficient than full factorial designs

  • Can estimate main effects and interactions with reduced experimental runs

  • Resolution V designs maintain ability to estimate main effects and two-way interactions

• Response Surface Method (RSM):

  • Ideal for optimization of conditions affecting atpF function

  • Can model main effects, interactions, and quadratic effects

  • Provides visual representation of optimal conditions

• Definitive Screening Design (DSD):

  • Emerging approach with excellent efficiency

  • With minimal experimental runs ((2 × number of factors) + 1), can define main effects and estimate quadratic effects

  • Best used when studying novel factors with unknown effects

Selection of the appropriate design should be based on:

• The specific research question

• Available resources

• Required precision

• Number of factors to be investigated

For structure-function studies, site-directed mutagenesis experiments focusing on conserved residues would be particularly valuable.

How does atpF structure in Nocardia farcinica compare to homologous proteins in other bacteria?

The ATP synthase subunit b (atpF) in N. farcinica shares structural similarities with homologous proteins in other bacteria, but with some notable distinctions:

Sequence Comparison:
N. farcinica atpF consists of 186 amino acids , which is consistent with atpF proteins from other bacteria in the Actinomycetales family. Homology analysis reveals higher sequence similarity with other mycobacterial species compared to more distant bacterial species.

Structural Features:

• A transmembrane domain at the N-terminus embedded in the membrane

• A cytoplasmic domain that interacts with the F1 sector

• A dimerization interface for forming the b-b subunit dimer

Comparative Table of atpF Proteins Across Selected Bacteria:

Understanding these structural relationships is important for:

• Interpreting experimental results

• Designing structure-based drug targeting strategies

• Predicting functional conservation or divergence

Comparative analysis of atpF across species can provide insights into the evolution of ATP synthase and adaptation mechanisms in different bacterial environments.

What role might atpF play in the drug resistance of Nocardia farcinica?

While atpF itself has not been directly implicated in drug resistance mechanisms of N. farcinica based on the provided search results, several hypotheses can be formulated based on the broader context of ATP synthase involvement in bacterial physiology:

Potential Mechanisms:

• Energy-Dependent Efflux Systems:
  ATP synthase generates ATP that powers membrane efflux pumps, which can expel antibiotics from bacterial cells. Altered ATP synthase function could impact the energy availability for these systems .

• Metabolic Adaptation:
  N. farcinica has demonstrated versatile metabolic capabilities, including diverse metabolic pathway genes and numerous oxygenases . ATP synthase function may be critical for energy provision during metabolic adaptations that confer resistance.

• Membrane Integrity:
  As part of the membrane-embedded F0 complex, atpF might influence membrane properties that affect antibiotic penetration.

Research Context:
N. farcinica has demonstrated resistance to multiple antibiotics, including:

• Rifampin (through an unusual mechanism involving duplicate copies of rpoB genes)

• Erythromycin, cefotaxime, and tobramycin

• Some strains have shown resistance to trimethoprim-sulfamethoxazole

While ATP synthase is not a direct target of these antibiotics, its role in energy metabolism makes it a potential indirect factor in resistance mechanisms, particularly those requiring energy-dependent processes.

Experimental approaches to investigate this relationship could include:

• Controlled expression studies of atpF and correlation with antibiotic susceptibility

• ATP synthesis measurement in resistant versus susceptible strains

• Membrane potential analysis in the context of antibiotic exposure

How can site-directed mutagenesis of atpF contribute to understanding its function?

Site-directed mutagenesis of atpF represents a powerful approach for dissecting the structure-function relationships of this protein:

Key Residues for Mutagenesis:

• Transmembrane Domain Residues:

  • Hydrophobic residues within the sequence "YDIVWSVVCVAIIAVVFYKY"

  • Mutations to more polar amino acids can assess the importance of membrane anchoring

• Interface Residues:

  • Charged and polar residues likely involved in interactions with other ATP synthase subunits

  • The region "GIAKAEAAQAEAQQTLEQYQQQ" contains several charged residues that may form salt bridges

• Conserved Motifs:

  • Residues conserved across bacterial species are prime candidates for functional importance

  • The C-terminal region often contains residues critical for F1 sector interaction

Methodological Approach:

• Design of Mutations:

  • Alanine scanning: Systematically replacing residues with alanine

  • Conservative vs. non-conservative substitutions

  • Deletion or insertion mutations in non-critical structural regions

• Expression Systems:

  • Use of the same E. coli system established for wild-type expression

  • Complementation studies in ATP synthase-deficient strains

• Functional Assays:

  • ATP synthesis/hydrolysis measurements

  • Proton translocation assays

  • Binding studies with other subunits

  • Structural integrity assessment via circular dichroism or thermal stability assays

• Analysis Framework:

  • Comparison to wild-type protein

  • Correlation of structural changes with functional impacts

  • Molecular modeling to interpret results

This systematic approach can reveal:

• Essential residues for catalytic function

• Structural elements required for proper assembly

• Regions involved in subunit interactions

• Potential sites for therapeutic targeting

What methodologies are recommended for studying the interaction of atpF with other ATP synthase subunits?

Investigating the interactions between atpF and other ATP synthase subunits requires a multifaceted approach:

Co-purification Methodologies:

• FLAG-Tag Affinity Purification:
  The use of FLAG-tagged proteins has proven effective for isolating intact ATP synthase complexes. A protocol using 3×FLAG tag fused to the beta subunit demonstrates this approach for obtaining enzymatically active complexes .

  Key steps:

  • Express FLAG-tagged atpF in appropriate system

  • Cell lysis under non-denaturing conditions

  • Capture on anti-FLAG resin

  • Gentle elution using 3×FLAG peptide

  • Analysis of co-purified proteins

• Co-immunoprecipitation:
  As noted in search result , "For co-immunoprecipitation assays, both 0.1 M glycine HCl (pH 3.5) or SDS-PAGE sample buffer can be considered for elution instead of the 3×FLAG peptide used here; in that case the eluted samples can proceed directly to SDS-PAGE, followed by mass spectrometry to identify protein components."

Interaction Analysis Techniques:

• Blue-Native PAGE:
  This technique maintains protein-protein interactions and can visualize intact ATP synthase complexes containing atpF .

• Crosslinking Mass Spectrometry:
  Chemical crosslinkers can capture transient interactions, followed by MS analysis to identify specific interaction sites between atpF and other subunits.

• Surface Plasmon Resonance (SPR):
  For quantitative measurement of binding kinetics between atpF and individual partner subunits.

• Förster Resonance Energy Transfer (FRET):
  When studying dynamics of interactions in real-time.

Advanced Structural Methods:

• Cryo-Electron Microscopy:
  For visualizing the complete ATP synthase structure and determining the exact positioning of atpF within the complex.

• X-ray Crystallography:
  If crystallization of subcomplexes containing atpF is achievable.

Functional Validation:

• Reconstitution Experiments:
  Combining purified components including atpF to restore ATP synthesis activity in liposomes or nanodiscs.

• Mutagenesis of Interface Residues:
  Strategic mutations at predicted interaction sites can validate their importance through disruption of binding or assembly.

How can recombinant atpF be used in diagnostic applications for Nocardia infections?

Recombinant atpF protein from N. farcinica has potential applications in diagnostic tools for Nocardia infections:

Antibody-Based Diagnostics:

• Antigen Production:
  Purified recombinant atpF can serve as an antigen for generating highly specific polyclonal or monoclonal antibodies against N. farcinica.

• Immunoassay Development:

  • ELISA-based detection systems using anti-atpF antibodies

  • Lateral flow assays for point-of-care diagnostics

  • Immunohistochemistry for tissue samples

PCR-Based Diagnostics:

• Species-Specific Detection:
  Similar to the approach used for N. farcinica identification through the 314-bp PCR fragment described in search result , atpF gene sequences could serve as targets for species-specific PCR-based diagnostics.

  The search results describe: "PCR amplification of genomic DNA from 28 N. farcinica isolates with Nf1 and Nf2 generated a single intense 314-bp fragment. The specificity of the assay with these primers was verified, since there were no PCR amplification products observed from heterologous nocardial species (n = 59) or other related bacterial genera (n = 41)."

• Design Considerations:

  • Primers targeting unique regions of the atpF gene

  • Optimization of PCR conditions for clinical samples

  • Validation against related Nocardia species

Metagenomic Approaches:

• Next-Generation Sequencing:
  The search results mention successful identification of N. farcinica infection using metagenomic next-generation sequencing (mNGS) . Similar approaches could incorporate atpF sequences as markers.

Practical Implementation:

When developing such diagnostic applications, researchers should consider:

• Sensitivity and specificity requirements for clinical use

• Sample preparation methods from various clinical specimens

• Validation against gold standard methods

• Integration with existing diagnostic workflows

Early and accurate diagnosis of N. farcinica infections is particularly important due to the organism's resistance to multiple antibiotics and the need for specific treatment approaches .

What experimental strategies are recommended for studying the role of atpF in Nocardia farcinica pathogenesis?

Investigating the role of atpF in N. farcinica pathogenesis requires a comprehensive experimental strategy:

Genetic Manipulation Approaches:

• Gene Knockout/Knockdown:

  • CRISPR-Cas9 systems adapted for Nocardia

  • Antisense RNA strategies

  • Construction of conditional mutants if atpF is essential

• Complementation Studies:

  • Re-introduction of wild-type or mutant atpF to confirm phenotypes

  • Expression under native or inducible promoters

Infection Models:

• In Vitro Cellular Models:

  • Macrophage infection assays to assess intracellular survival

  • Epithelial cell adhesion and invasion studies

  • Co-culture systems mimicking host environments

• Animal Models:

  • Mouse models of pulmonary or disseminated nocardiosis

  • Assessment of bacterial burden, histopathology, and immune response

  • Comparison of wild-type and atpF-modified strains

Molecular Pathogenesis Studies:

• Transcriptomic Analysis:

  • RNA-seq to identify genes co-regulated with atpF during infection

  • Comparison of expression patterns between environmental and host conditions

• Metabolic Profiling:

  • Assessment of energy metabolism in wild-type vs. atpF-modified strains

  • Analysis of metabolic adaptation to host environments

• Protein-Protein Interaction Studies:

  • Identification of host proteins that might interact with ATP synthase components

  • Investigation of potential moonlighting functions of atpF beyond energy metabolism

Clinical Correlation:

• Analysis of Clinical Isolates:

  • Sequencing of atpF in clinical isolates with varying virulence

  • Correlation of atpF sequence variants with disease severity or presentation

The search results highlight N. farcinica's ability to cause severe infections, including pneumonia, central nervous system involvement, and cutaneous tissues . Understanding atpF's role in the pathogen's energy metabolism during infection could provide insights into its adaptation to different host environments and potential vulnerabilities for therapeutic targeting.

What are the challenges in purifying functional atpF and how can they be overcome?

Purification of functional atpF presents several challenges due to its nature as a membrane protein component of a larger complex:

Key Challenges and Solutions:

• Membrane Protein Solubilization:

  Challenge: atpF contains hydrophobic transmembrane domains that make it difficult to solubilize while maintaining native structure.

  Solutions:

  • Use mild detergents (DDM, LMNG, or digitonin) to preserve protein integrity

  • Implement detergent screening to identify optimal conditions

  • Consider amphipols or nanodiscs for stabilization after purification

• Maintaining Functional State:

  Challenge: Isolated atpF may lose functional capacity when separated from the ATP synthase complex.

  Solutions:

  • Co-expression with interacting subunits

  • Rapid purification at 4°C to minimize degradation

  • Addition of stabilizing agents (glycerol, specific lipids)

  • Consider purifying the entire ATP synthase complex, as demonstrated in the FLAG-tag protocol

• Expression Levels:

  Challenge: Membrane proteins often express poorly in heterologous systems.

  Solutions:

  • Optimize codon usage for the expression host

  • Test different promoter strengths and induction conditions

  • Use specialized E. coli strains (C41, C43) designed for membrane protein expression

  • Consider fusion partners that enhance expression (SUMO, MBP)

• Protein Purity Assessment:

  Challenge: Contaminating proteins may co-purify with atpF.

  Solutions:

  • Implement multi-step purification strategies

  • Validate purity using complementary methods (SDS-PAGE, Western blot, mass spectrometry)

  • Use size exclusion chromatography as a final polishing step

Practical Protocol Adaptations:

Based on successful ATP synthase purification methods , the following specific recommendations can be made:

• Buffer composition: Include phospholipids to stabilize the membrane protein

• Purification approach: Consider FLAG-tagged constructs for gentle, high-affinity purification

• Storage conditions: Store in buffer containing 50% glycerol at -20°C for extended stability

• Quality control: Assess both purity (≥85-90%) and functional state before experimental use

How does ATP synthase structure and function in Nocardia farcinica compare to that in other bacterial pathogens?

ATP synthase in N. farcinica shares fundamental structural and functional principles with other bacteria, but with important distinctions that may relate to its pathogenic lifestyle:

Structural Comparison:

Functional Considerations:

• Energy Metabolism Adaptation:
  N. farcinica possesses extensive metabolic capabilities evidenced by its large genome (6.02 Mb) and numerous oxygenases. Its ATP synthase may be adapted to function under the diverse metabolic conditions encountered during environmental survival and host infection.

• Drug Targeting Potential:
  While ATP synthase has emerged as a drug target in Mycobacteria (e.g., bedaquiline targeting the c subunit), the specific vulnerability of N. farcinica ATP synthase remains unexplored. The search results indicate that N. farcinica possesses various resistance mechanisms, including to rifampin , suggesting it may have evolved unique features in essential complexes like ATP synthase.

• Regulatory Mechanisms:
  The regulation of ATP synthase expression and activity in N. farcinica likely reflects its ability to adapt to different environmental conditions, including the host environment during infection.

Research Implications:

Understanding these comparisons can inform:

• Potential drug development strategies targeting N. farcinica ATP synthase

• Evolutionary adaptations of ATP synthase in actinobacterial pathogens

• Mechanisms of metabolic adaptation during the infection process

The search results highlight N. farcinica's versatility and adaptability , which likely extends to the function of its essential energy-generating machinery including ATP synthase and its atpF component.

What RNA-based methods can be used to study atpF expression and regulation in Nocardia farcinica?

Several RNA-based methodologies can be employed to investigate the expression patterns and regulatory mechanisms of atpF in N. farcinica:

Quantitative Expression Analysis:

• RT-qPCR:

  • Design primers specific to atpF mRNA sequence

  • Optimize for the high G+C content (70.8%) of N. farcinica

  • Include appropriate reference genes for normalization

  • Apply to study expression under various conditions (e.g., growth phase, stress, infection models)

• RNA-Seq:

  • Provides genome-wide transcriptional context for atpF expression

  • Reveals co-regulated genes and potential operonic structure

  • Can identify antisense transcripts or other regulatory RNAs affecting atpF

  • Useful for comparing expression profiles between environmental and host conditions

Regulatory Mechanism Investigation:

• 5' RACE (Rapid Amplification of cDNA Ends):

  • Identifies transcription start sites and potential promoter regions

  • Reveals the presence of untranslated regions that may contain regulatory elements

• Reporter Gene Fusions:

  • Construct fusions of atpF promoter region with reporter genes (GFP, luciferase)

  • Test promoter activity under different conditions

  • Identify regulatory elements through deletion analysis

• RNA Stability Assays:

  • Use transcription inhibitors (e.g., rifampicin) followed by time-course sampling

  • Measure atpF mRNA decay rates under different conditions

  • Connect to post-transcriptional regulatory mechanisms

Advanced Approaches:

• Ribosome Profiling:

  • Provides insight into translational efficiency of atpF

  • Identifies potential translational regulation mechanisms

• RNA Structure Probing:

  • Investigates secondary structures in atpF mRNA that may affect expression

  • Methods include SHAPE (Selective 2'-hydroxyl acylation analyzed by primer extension) and DMS probing

• RNA Immunoprecipitation:

  • Identifies RNA-binding proteins that may regulate atpF expression

  • Can reveal post-transcriptional regulatory mechanisms

Contextual Considerations:

The search results indicate that N. farcinica has a complex genome with numerous metabolic and resistance genes . The atpF gene likely functions as part of an operon encoding multiple ATP synthase subunits, similar to other bacteria. Understanding its expression patterns may provide insights into the energy metabolism adaptation of this pathogen during infection and environmental survival.

What experimental designs are appropriate for structure-function studies of recombinant atpF?

Structure-function studies of recombinant atpF require careful experimental design to generate meaningful insights:

Structural Analysis Approaches:

• X-ray Crystallography:

  • Challenging for membrane proteins but could be attempted with:

    • Detergent-solubilized protein

    • Lipidic cubic phase crystallization

    • Co-crystallization with antibody fragments

• Cryo-Electron Microscopy:

  • Increasingly powerful for membrane proteins

  • Can visualize atpF in the context of the entire ATP synthase complex

  • Provides insights into structural arrangements and interactions

• NMR Spectroscopy:

  • Suitable for specific domains or peptide fragments of atpF

  • Can provide dynamic information not available from static methods

Functional Correlation Designs:

• Systematic Mutagenesis:
  The following design approaches can maximize information yield:

  • Factorial Design: Test multiple mutations and their interactions

  • Response Surface Method: Optimize conditions for functional assays

  • Alanine Scanning: Systematically replace residues to identify essential ones

• Domain Swapping Experiments:

  • Replace domains of atpF with homologous regions from related bacteria

  • Test chimeric proteins for function to identify species-specific features

• Cross-linking Studies:

  • Use chemical or photo-crosslinkers to capture interaction interfaces

  • Identify crosslinked products by mass spectrometry

Biophysical Analysis:

• Circular Dichroism:

  • Assess secondary structure content and stability

  • Monitor structural changes under different conditions

• Thermal Shift Assays:

  • Measure protein stability

  • Identify conditions or ligands that stabilize the protein

• Hydrogen-Deuterium Exchange Mass Spectrometry:

  • Map solvent-accessible regions

  • Identify structural dynamics and binding interfaces

Integration with Computational Methods:

• Molecular Dynamics Simulations:

  • Model atpF behavior in membrane environments

  • Predict effects of mutations on structure and dynamics

• Homology Modeling:

  • Generate structural models based on related proteins

  • Guide experimental design for validation

For optimal results, a mixed-methods approach combining multiple techniques should be employed. The definitive screening design (DSD) approach mentioned in search result can be particularly valuable for efficiently exploring multiple factors with minimal experimental runs.

How can proteomics approaches be used to study atpF interactions in the context of Nocardia farcinica physiology?

Proteomics offers powerful tools for studying atpF in the broader context of N. farcinica physiology:

Interactome Analysis:

• Affinity Purification-Mass Spectrometry (AP-MS):

  • Express tagged atpF in N. farcinica

  • Purify under native conditions to maintain protein-protein interactions

  • Identify co-purifying proteins by mass spectrometry

  • Filter against appropriate controls to identify specific interactors

• Proximity Labeling:

  • Fuse atpF to enzymes like BioID or APEX2

  • These enzymes biotinylate proteins in close proximity

  • Identify labeled proteins through streptavidin purification and MS

  • Particularly valuable for capturing transient interactions

• Chemical Cross-linking MS (XL-MS):

  • Use chemical cross-linkers to stabilize protein-protein interactions

  • Digest and identify cross-linked peptides by MS

  • Provides spatial constraints for modeling interaction interfaces

Quantitative Proteomics:

• Differential Expression Analysis:

  • Compare protein abundance in wild-type vs. atpF-modified strains

  • Identify proteins whose levels change in response to ATP synthase perturbation

  • Methods include SILAC, TMT, or label-free quantification

• Pulse-Chase Proteomics:

  • Study protein turnover rates using stable isotope labeling

  • Determine if atpF perturbation affects protein synthesis or degradation rates

Structural Proteomics:

• Limited Proteolysis:

  • Probe structural features of atpF through controlled digestion

  • Compare accessibility patterns between different conditions

  • Identify protected regions indicating binding interfaces

• Hydrogen-Deuterium Exchange MS:

  • Map solvent accessibility of atpF regions

  • Compare exchange patterns in different functional states

  • Identify regions involved in protein-protein interactions

Systems-Level Analysis:

• Protein Correlation Profiling:

  • Fractionate cellular components (e.g., by centrifugation or chromatography)

  • Identify proteins with similar distribution profiles to atpF

  • Infer functional associations based on co-localization

• Multi-omics Integration:

  • Combine proteomics data with transcriptomics and metabolomics

  • Create integrated models of how atpF and ATP synthase function relates to broader cellular physiology

  • Particularly relevant given N. farcinica's complex metabolism and adaptation mechanisms