Recombinant Shigella boydii serotype 18 ATP synthase subunit b (atpF)

What is the genomic organization of the atpF gene in Shigella boydii serotype 18?

The atpF gene in S. boydii is part of the ATP operon, which typically includes eight genes encoding the subunits of ATP synthase. In Enterobacteriaceae, which includes Shigella, the gene order is generally conserved: atpIBEFHAGDC. The atpF gene specifically encodes the b subunit, which forms part of the peripheral stalk connecting the F₁ and F₀ domains. Gene prediction and annotation tools such as GeneMarkS and RAST, followed by BLASTP and BLASTN against UniProt and NR databases, can be used to accurately identify and characterize the atpF gene in S. boydii serotype 18 . When analyzing the genomic context, it's important to consider potential mobile genetic elements that may have altered the gene organization, particularly in clinical isolates, as S. boydii has been shown to readily acquire mobile elements carrying resistance determinants .

How does the amino acid sequence of ATP synthase subunit b in S. boydii serotype 18 compare to other Shigella species?

• Perform multiple sequence alignments using tools like CLUSTAL Omega or MUSCLE

• Calculate sequence identity and similarity percentages

• Identify conserved domains and variable regions

• Map amino acid substitutions onto known structural models

These comparative analyses can reveal evolutionary relationships and potential functional differences. The analysis should consider that while core functional domains are typically conserved, surface-exposed regions may show greater variability. Such variations might reflect adaptations to different ecological niches or immune pressures, as has been observed with other membrane proteins in Shigella species .

What are the structural characteristics of ATP synthase subunit b in S. boydii?

ATP synthase subunit b in S. boydii likely shares the general structural features found in other Enterobacteriaceae:

• N-terminal membrane-anchoring domain (hydrophobic)

• Long α-helical coiled-coil domain that extends from the membrane

• C-terminal domain that interacts with the δ subunit of the F₁ portion

Structural prediction based on homology modeling can provide insights into the specific conformation of S. boydii atpF. Conformational changes induced by ATP binding and hydrolysis are likely critical for the function of ATP synthase, as suggested by study titles in the literature . When performing structural analysis, researchers should consider using multiple prediction algorithms and validation methods to ensure accuracy, particularly for the membrane-spanning regions which are more challenging to model correctly.

What expression systems are most effective for producing recombinant S. boydii ATP synthase subunit b?

For recombinant expression of S. boydii ATP synthase subunit b, several expression systems can be considered:

When choosing an expression system, consider that membrane proteins like ATP synthase subunit b often present challenges in recombinant expression. The standard procedure would involve PCR amplification of the atpF gene from S. boydii genomic DNA, cloning into an appropriate expression vector, and transformation into the chosen host. Similar molecular cloning approaches have been successfully used for analyzing genes from S. boydii, as demonstrated in previous studies .

What are the optimal conditions for purifying recombinant S. boydii ATP synthase subunit b?

Purification of recombinant ATP synthase subunit b requires careful consideration of its membrane-associated nature:

• Cell lysis: French press or sonication in buffer containing mild detergents (e.g., DDM, LDAO)

• Initial purification: Immobilized metal affinity chromatography (IMAC) using His-tag

• Secondary purification: Size exclusion chromatography or ion-exchange chromatography

• Quality assessment: SDS-PAGE, Western blot, mass spectrometry

Critical parameters to optimize include:

• Detergent type and concentration (to maintain protein stability while solubilizing membranes)

• Buffer composition (pH, salt concentration, presence of glycerol as stabilizer)

• Temperature (typically 4°C throughout purification)

• Addition of protease inhibitors to prevent degradation

For functional studies, it may be necessary to reconstitute the purified protein into liposomes or nanodiscs to maintain its native conformation. When developing purification protocols, researchers should consider that improper detergent selection can lead to protein aggregation or denaturation, particularly for membrane-spanning segments of the protein.

How can researchers verify the proper folding and functionality of recombinant S. boydii ATP synthase subunit b?

Verifying proper folding and functionality of recombinant ATP synthase subunit b requires multiple complementary approaches:

• Circular dichroism (CD) spectroscopy: To assess secondary structure content (expected high α-helical content)

• Thermal shift assays: To evaluate protein stability and the effect of different buffer conditions

• Limited proteolysis: To probe the accessibility of protease cleavage sites as an indicator of folding

• Functional reconstitution: Assembly with other ATP synthase subunits to form functional complexes

• ATP hydrolysis assays: To measure enzymatic activity when assembled in the complete complex

• Interaction studies: Using techniques like isothermal titration calorimetry (ITC) or surface plasmon resonance (SPR) to verify binding to other subunits

Structural studies using X-ray crystallography or cryo-electron microscopy would provide the most definitive evidence of proper folding but are technically challenging. Researchers should be aware that conformational changes in ATP synthase subunits are critical for function, as indicated by studies on ATP-induced conformational changes . The functional validation should consider that the b subunit alone may not show enzymatic activity, as it functions as part of the larger ATP synthase complex.

What are the key considerations when designing experiments to study the role of ATP synthase subunit b in S. boydii virulence?

Studying the role of ATP synthase subunit b in S. boydii virulence requires a multifaceted experimental approach:

• Gene knockout/knockdown studies:

  • Create atpF deletion mutants using homologous recombination or CRISPR-Cas9

  • Develop conditional expression systems to study essential genes

  • Assess the impact on growth, ATP production, and virulence phenotypes

• Site-directed mutagenesis:

  • Target conserved residues identified through sequence alignment

  • Evaluate the effect of mutations on protein function and bacterial fitness

• Infection models:

  • Cell culture-based assays (e.g., invasion of epithelial cells)

  • Animal models of Shigella infection (considering ethical approvals )

  • Assessment of bacterial load, tissue damage, and host immune response

• Transcriptomic/proteomic analyses:

  • Compare wild-type and atpF-mutant strains under various conditions

  • Identify differentially expressed genes/proteins in response to atpF mutation

When designing these experiments, it's important to include appropriate controls and consider potential polar effects of genetic manipulations. ATP synthase function is essential for energy metabolism, so complete knockout may be lethal, necessitating careful experimental design. Researchers should also consider that S. boydii, like other Shigella species, has adapted specific virulence mechanisms, potentially including modifications to metabolic enzymes like ATP synthase .

How can researchers effectively study the interaction between ATP synthase subunit b and other components of the ATP synthase complex in S. boydii?

Several methodologies can be employed to study protein-protein interactions within the ATP synthase complex:

• Co-immunoprecipitation: Using antibodies against tagged versions of atpF to pull down interacting partners

• Bacterial two-hybrid systems: To screen for interacting proteins in vivo

• Crosslinking studies: To capture transient interactions followed by mass spectrometry analysis

• FRET/BRET analysis: For studying interactions in living cells using fluorescent or bioluminescent tags

• Surface plasmon resonance (SPR): For quantitative analysis of binding kinetics

• Hydrogen-deuterium exchange mass spectrometry (HDX-MS): To map interaction interfaces

Data interpretation should consider the dynamic nature of these interactions and potential conformational changes induced by ATP binding and hydrolysis . When designing interaction studies, researchers should be mindful that membrane proteins require special consideration, often necessitating the use of detergents or membrane-mimetic systems that may affect interaction dynamics.

What approaches can be used to investigate the effect of antimicrobial compounds on S. boydii ATP synthase function?

ATP synthase is a potential target for antimicrobial development. To investigate the effects of compounds on S. boydii ATP synthase:

• Enzymatic assays:

  • ATP synthesis/hydrolysis assays with purified enzyme or membrane preparations

  • Measurement of proton translocation using pH-sensitive fluorescent dyes

  • Determination of IC₅₀ values for potential inhibitors

• Bacterial growth studies:

  • Minimum inhibitory concentration (MIC) determination

  • Time-kill kinetics

  • Synergy testing with established antibiotics

• Resistance development:

  • Serial passage experiments to assess resistance emergence

  • Whole genome sequencing to identify resistance mutations

  • Structure-activity relationship studies to optimize inhibitor design

• Structural studies:

  • Co-crystallization or cryo-EM studies with inhibitors

  • Molecular docking and simulation to predict binding modes

  • Hydrogen-deuterium exchange mass spectrometry to detect inhibitor-induced conformational changes

Given the rising antimicrobial resistance in Shigella species, including resistance to first-line antibiotics like ciprofloxacin, ceftriaxone, and azithromycin , targeting essential metabolic enzymes like ATP synthase presents a promising alternative therapeutic strategy. Researchers should design experiments that can distinguish between specific effects on ATP synthase and general cellular toxicity.

How should researchers analyze structural data when comparing ATP synthase subunit b from different Shigella strains?

When analyzing structural data for ATP synthase subunit b across different Shigella strains:

• Multiple sequence alignment interpretation:

  • Identify conserved vs. variable regions

  • Map conservation scores onto structural models

  • Correlate sequence variations with potential functional differences

• Homology model evaluation:

  • Use multiple validation metrics (QMEAN, ProSA, Ramachandran plots)

  • Compare models generated using different templates

  • Assess the quality of membrane-spanning regions separately from soluble domains

• Molecular dynamics simulation analysis:

  • Calculate root mean square deviation (RMSD) and fluctuation (RMSF)

  • Analyze hydrogen bonding networks and salt bridges

  • Identify conformational changes during simulations

• Structure-function correlation:

  • Map functionally important residues onto the structure

  • Predict the impact of natural variants using computational tools

  • Design validation experiments based on structural insights

Statistical approaches should be employed to quantify structural differences, and visualization tools should be used to highlight key features. When interpreting results, researchers should consider that conformational flexibility is important for ATP synthase function, and static structures may not capture the full range of conformational states that exist in vivo .

What statistical approaches are most appropriate for analyzing ATP synthase activity data in S. boydii mutant studies?

For analyzing ATP synthase activity data in mutant studies:

Sample size calculations should be performed before experiments to ensure adequate statistical power. When interpreting results, consider both statistical and biological significance, as small statistically significant changes may not be biologically relevant. Data visualization using boxplots, scatter plots, or violin plots can help identify patterns and potential outliers in the data.

How can researchers interpret contradictory results when studying the role of ATP synthase in S. boydii pathogenesis?

Contradictory results can arise from various sources when studying complex biological systems:

• Reconciling contradictory findings:

  • Consider differences in experimental conditions (media, growth phase, oxygen levels)

  • Examine strain differences (clinical isolates vs. lab strains)

  • Evaluate the sensitivity and specificity of different assays

  • Assess whether differences are quantitative (magnitude) or qualitative (direction)

• Addressing technical variability:

  • Implement rigorous controls and standardized protocols

  • Use multiple complementary techniques to verify findings

  • Consider the impact of tags or fusion proteins on protein function

  • Validate key findings using independent methodologies

• Biological interpretations:

  • Consider context-dependent effects (host cell type, infection stage)

  • Evaluate compensatory mechanisms that may mask phenotypes

  • Assess potential polar effects from genetic manipulations

  • Recognize that ATP synthase function may vary under different conditions

When faced with contradictory results, researchers should avoid confirmation bias and objectively evaluate all evidence. For example, while one study found that Acanthamoebae castellanii could phagocytose S. sonnei and protect it from environmental damage, a more recent study showed that S. sonnei could not survive in A. castellanii cytosol . Such contradictions highlight the importance of experimental details and the evolving nature of scientific understanding.

How can structural information about S. boydii ATP synthase subunit b contribute to drug discovery efforts?

Structural information about ATP synthase subunit b can facilitate drug discovery through several approaches:

• Structure-based drug design:

  • Identification of potential binding pockets through computational analysis

  • Virtual screening of compound libraries against identified targets

  • Fragment-based drug discovery focusing on critical functional regions

  • Design of peptide inhibitors that disrupt subunit interactions

• Targeting unique features:

  • Comparative analysis with human ATP synthase to identify bacteria-specific regions

  • Focus on interfaces between subunits that may be less conserved

  • Design of allosteric inhibitors that affect conformational changes

• Rational optimization:

  • Structure-activity relationship studies to improve potency and selectivity

  • Pharmacophore modeling based on structural insights

  • Modification of existing inhibitors guided by structural information

• Resistance prediction and prevention:

  • Identification of potential resistance hotspots through structural analysis

  • Design of inhibitors with high barriers to resistance

  • Development of combination strategies targeting multiple sites

With the increasing prevalence of antimicrobial resistance in Shigella species, including resistance to ciprofloxacin, ceftriaxone, and azithromycin , new targets for antibiotic development are urgently needed. ATP synthase represents a promising target due to its essential role in bacterial energy metabolism.

What gene editing approaches can be used to study the function of specific domains within ATP synthase subunit b in S. boydii?

Modern gene editing approaches offer precise tools for functional domain analysis:

• CRISPR-Cas9 for genome editing:

  • Creation of precise point mutations to target specific residues

  • Domain swapping between different species to create chimeric proteins

  • Introduction of small deletions or insertions to assess domain function

  • Implementation of base editors for specific nucleotide changes

• Recombineering approaches:

  • λ Red recombination for scarless genome editing

  • Multiplex automated genome engineering (MAGE) for creating variant libraries

  • Site-specific recombination systems for conditional modifications

• Domain-focused mutagenesis strategies:

  • Alanine scanning of targeted regions

  • Introduction of cysteine pairs for disulfide crosslinking studies

  • Conservative vs. non-conservative substitutions to probe function

  • Insertion of flexible linkers to assess domain independence

• Conditional expression systems:

  • Degron tags for inducible protein degradation

  • Split protein complementation to study domain interactions

  • Promoter swapping for controlled expression levels

When applying these techniques to S. boydii, researchers should consider potential barriers to genetic manipulation, such as restriction-modification systems or intrinsic recombination resistance. Adaptation of protocols successful in related Enterobacteriaceae like E. coli may be necessary, with appropriate modifications based on the specific characteristics of S. boydii .

How can systems biology approaches be applied to understand the role of ATP synthase in the broader metabolic network of S. boydii?

Systems biology offers powerful frameworks to integrate ATP synthase function into broader metabolic contexts:

• Metabolic network reconstruction and analysis:

  • Genome-scale metabolic modeling to predict the impact of ATP synthase perturbations

  • Flux balance analysis to quantify metabolic rewiring in response to ATP limitations

  • Metabolic control analysis to determine the control coefficient of ATP synthase

  • Integration of transcriptomic and proteomic data to constrain metabolic models

• Multi-omics integration:

  • Combined analysis of transcriptomics, proteomics, and metabolomics data

  • Correlation networks to identify genes/proteins with similar expression patterns

  • Enrichment analysis to identify pathways affected by ATP synthase dysfunction

  • Time-course experiments to capture dynamic responses

• Protein-protein interaction networks:

  • Identification of ATP synthase-centered interaction hubs

  • Analysis of interaction changes under different environmental conditions

  • Comparison of interaction networks across Shigella species and strains

  • Integration with structural data to understand interaction mechanisms

• Host-pathogen interaction modeling:

  • Dual metabolic modeling of host and pathogen metabolism

  • Identification of metabolic vulnerabilities during infection

  • Analysis of energy requirements during different stages of infection

  • Integration with immune response models

Systems biology approaches can help researchers understand how S. boydii adapts its energy metabolism during infection and in response to environmental stresses, potentially revealing new therapeutic targets. When implementing these approaches, the choice of appropriate control conditions and careful experimental design are critical for meaningful interpretation of the complex datasets generated.