Recombinant Neisseria meningitidis serogroup C / serotype 2a ATP synthase subunit b (atpF)

What is Neisseria meningitidis serogroup C and how is it classified?

Neisseria meningitidis is a Gram-negative oral commensal bacterium that can opportunistically cause septicemia and/or meningitis . The bacteria are classified into 13 distinct serogroups based on the serological differences of their polysaccharide capsules, with serogroups A, B, C, W, X, and Y being responsible for invasive meningococcal disease . Serogroup C specifically is one of the major disease-causing serogroups and was historically designated as type II-α based on agglutination reactions with immune rabbit serum before the current nomenclature was established . The polysaccharide capsule is the primary virulence determinant for this pathogen, and in the case of serogroup C, forms the basis for polysaccharide conjugate vaccines that have been developed to prevent invasive disease .

What is the functional significance of ATP synthase in N. meningitidis metabolism?

ATP synthase plays a critical role in the energy metabolism of N. meningitidis by catalyzing the synthesis of ATP from ADP and inorganic phosphate using the proton gradient across the cell membrane. While not explicitly detailed in the provided search results, this function is especially significant for N. meningitidis which must adapt to different nutritional environments during colonization and invasion. Research has identified that N. meningitidis grows on a limited range of nutrients during infection, with glucose being the main energy source available in human blood . The HexR transcriptional regulator controls genes of central carbon metabolism in response to glucose availability, suggesting a tightly regulated energy metabolism network in which ATP synthase would be a crucial component . The proper functioning of energy generation systems like ATP synthase would be essential for the bacterium's survival in different host environments and during the transition from commensal to pathogenic states.

How does genetic variation in atpF influence research approaches?

Genetic variation in bacterial genes can significantly impact research reproducibility and experimental design. In the case of N. meningitidis, substantial genetic polymorphism has been observed in various genes. For example, in the RecG gene, 49 single nucleotide polymorphisms (SNPs) have been identified across N. meningitidis genomes, including 37 non-synonymous SNPs that could affect protein function . Similar variation might be expected in the atpF gene, necessitating careful consideration when selecting strains for research. When designing experiments involving atpF, researchers should sequence the gene from their working strains to identify any variations that might affect protein expression, structure, or function. Additionally, researchers should consider using reference strains with well-characterized genomes to ensure reproducibility across different laboratories.

What expression systems are most effective for producing functional recombinant N. meningitidis ATP synthase subunit b?

Based on successful approaches with other N. meningitidis proteins, Escherichia coli is likely the most suitable expression system for recombinant production of ATP synthase subunit b. In related research, transferrin binding proteins TbpA and TbpB from N. meningitidis isolate K454 were successfully overexpressed in E. coli while retaining their ability to bind human transferrin . Similarly, the RecG helicase from N. meningitidis has been successfully overexpressed and purified in functional form . When expressing membrane proteins like ATP synthase subunit b, specialized E. coli strains such as C41(DE3) or C43(DE3), which are designed for membrane protein expression, may provide better results than standard strains.

The expression construct should include:

• A strong inducible promoter (such as T7)

• An appropriate affinity tag (His-tag or GST) for purification

• Optional solubility-enhancing fusion partners for improved folding

• Codon optimization for E. coli if expression levels are poor

Temperature, induction time, and inducer concentration should be optimized to minimize inclusion body formation, which is common with membrane proteins. Typically, lower temperatures (16-25°C) and reduced inducer concentrations yield better results for membrane protein expression.

What purification strategies yield the highest purity and activity for recombinant atpF?

Purification of membrane proteins like ATP synthase subunit b requires specialized approaches. Based on successful purification of other N. meningitidis proteins, a multi-step purification process is recommended:

• Membrane fraction isolation: Bacterial cells should be lysed, and the membrane fraction isolated by ultracentrifugation.

• Detergent solubilization: Select an appropriate detergent (e.g., n-dodecyl-β-D-maltoside, LDAO, or Triton X-100) to solubilize the membrane fraction while maintaining protein function.

• Affinity chromatography: If the recombinant protein contains an affinity tag, use the appropriate affinity resin. For example, the transferrin binding proteins from N. meningitidis were successfully purified using affinity chromatography based on their ability to bind human transferrin . For AtpF, a His-tag purification might be more universally applicable.

• Size exclusion chromatography: This final step removes aggregates and improves homogeneity of the sample.

Throughout the purification process, it is essential to maintain conditions that preserve protein activity, including appropriate buffer pH (typically 7.0-8.0), salt concentration, and the continued presence of detergent at concentrations above the critical micelle concentration.

How can researchers assess the structural integrity and functionality of purified recombinant atpF?

Multiple complementary approaches should be employed to verify both structural integrity and functionality of purified recombinant ATP synthase subunit b:

• Structural integrity assessment:

  • SDS-PAGE and western blotting to confirm protein size and identity

  • Circular dichroism (CD) spectroscopy to evaluate secondary structure content

  • Limited proteolysis to assess proper folding

  • Thermal stability assays to determine protein stability

• Functional assessment:

  • Binding assays with other ATP synthase subunits

  • Reconstitution into liposomes followed by proton pumping assays

  • ATP hydrolysis assays when combined with other ATP synthase components

• Structural characterization:

  • Negative-stain electron microscopy to visualize the protein

  • Cryo-electron microscopy for higher-resolution structural information

  • X-ray crystallography if crystals can be obtained

These approaches follow similar principles to those used in characterizing other N. meningitidis proteins such as RecG, which was assessed for ATP-dependent DNA binding and unwinding activities in vitro on various DNA model substrates .

How does N. meningitidis ATP synthase subunit b interact with other components of the ATP synthase complex?

ATP synthase subunit b (AtpF) serves as a critical structural component of the ATP synthase complex, forming part of the peripheral stalk that connects the membrane-embedded F0 sector with the catalytic F1 sector. While specific interaction data for N. meningitidis ATP synthase is not provided in the search results, the conserved nature of ATP synthase across bacterial species suggests the following interactions:

• Membrane anchoring: The N-terminal region of subunit b likely contains a transmembrane helix that anchors the protein in the bacterial membrane within the F0 sector.

• Dimerization: Two copies of subunit b typically form a right-handed coiled-coil structure that extends from the membrane to the F1 sector.

• Interaction with subunit delta (AtpH): The C-terminal region of subunit b interacts with the delta subunit of the F1 sector, helping to hold the catalytic alpha/beta subunits in position relative to the rotating central stalk.

• Interaction with subunit a (AtpB): Within the membrane, subunit b likely interacts with subunit a, contributing to the stability of the F0 complex.

These interactions are essential for the proper assembly and function of the ATP synthase complex, allowing it to couple proton translocation across the membrane with ATP synthesis.

What structural features distinguish N. meningitidis serogroup C atpF from other bacterial species?

While specific structural information about N. meningitidis serogroup C ATP synthase subunit b is not explicitly provided in the search results, several features might distinguish it from other bacterial species:

• Sequence variations: Like other N. meningitidis proteins, atpF likely contains sequence polymorphisms across different strains and serogroups. For example, the RecG gene in N. meningitidis contains 49 single nucleotide polymorphisms (SNPs) across different genomes, including 37 non-synonymous SNPs . Similar variation might exist in atpF.

• Adaptation to host environment: N. meningitidis proteins often show adaptations to the human host environment. For instance, the transferrin binding proteins specifically bind human transferrin , and the HexR regulator responds to glucose levels found in human blood . ATP synthase might similarly show adaptations related to functioning optimally in the unique environmental conditions encountered during meningococcal infection.

• Potential DNA uptake sequences (DUS): Some N. meningitidis genes contain an unusually high number of DNA uptake sequences that facilitate transformation. For example, the RecG gene contains an unusually high number of DUS . The presence of such sequences in or around the atpF gene could influence its evolution and genetic exchange.

A comprehensive structural analysis using techniques such as X-ray crystallography or cryo-electron microscopy would be necessary to identify specific structural features that distinguish N. meningitidis atpF from other bacterial homologs.

How can ATP synthase be targeted for potential antimicrobial development against N. meningitidis?

ATP synthase represents a promising antimicrobial target due to its essential role in bacterial energy metabolism. Several approaches could be employed for targeting N. meningitidis ATP synthase:

• Small molecule inhibitors: Develop compounds that specifically bind to and inhibit ATP synthase subunits. Potential binding sites include:

  • The interface between subunit b and other ATP synthase components

  • The proton channel within the F0 sector

  • The catalytic sites in the F1 sector

• Peptide-based inhibitors: Design peptides that mimic natural interaction surfaces between ATP synthase subunits, thereby disrupting complex assembly.

• Antibody-based approaches: Generate antibodies against exposed regions of ATP synthase components, which could be especially relevant for N. meningitidis given the success of protein-based vaccine approaches for this pathogen .

• CRISPR-Cas9 or antisense RNA strategies: Target the atpF gene or its mRNA to reduce expression of ATP synthase subunit b.

Each approach should be evaluated for specificity to avoid targeting human ATP synthase. Research into protein-based meningococcal vaccines has shown that bacterial surface proteins can provide protection against infection , suggesting that if portions of ATP synthase are surface-exposed, they might also serve as promising antimicrobial targets.

What role does ATP synthase play in N. meningitidis adaptation to different host environments?

The ability of N. meningitidis to adapt to different nutritional environments is crucial for its transition from a commensal organism to a pathogen. ATP synthase likely plays a significant role in this adaptive process:

• Metabolic flexibility: N. meningitidis must adapt to different energy sources as it moves from the nasopharynx to the bloodstream. Research has shown that glucose is the main energy source available in human blood, and N. meningitidis has specific regulatory mechanisms to respond to glucose availability through the HexR transcriptional regulator . ATP synthase activity would need to be coordinated with these changing metabolic pathways to maintain energy homeostasis.

• Response to environmental stress: During infection, N. meningitidis encounters various stresses including oxidative stress, pH changes, and nutrient limitation. ATP synthase function might be modulated under these conditions to optimize energy production.

• Virulence regulation: Energy metabolism is often linked to virulence factor expression in pathogenic bacteria. The finding that N. meningitidis strains lacking the HexR regulator were deficient in establishing successful bacteremia suggests a link between central metabolism and virulence. ATP synthase, as a key component of energy metabolism, might indirectly influence virulence factor expression.

• Biofilm formation: ATP levels could influence biofilm formation and persistence, which are important for colonization of the nasopharynx.

Understanding how ATP synthase activity is regulated in response to changing environments could provide insights into meningococcal pathogenesis and identify potential intervention points.

How does the expression and regulation of atpF correlate with virulence in clinical isolates?

The relationship between atpF expression and virulence in N. meningitidis could be complex and multifaceted:

• Transcriptional regulation: While not specifically mentioned for atpF, the search results indicate that N. meningitidis employs sophisticated transcriptional regulation in response to environmental cues. For example, the HexR regulator controls metabolic genes in response to glucose . Similar regulatory mechanisms might control atpF expression under different conditions encountered during infection.

• Post-transcriptional regulation: The genome-wide RNA compendium of N. meningitidis has revealed an extensive post-transcriptional regulatory network involving the RNA chaperone Hfq, 23 sRNAs, and hundreds of potential mRNA targets . This regulatory layer could include atpF, adding another dimension to its expression control.

• Genetic variation: Clinical isolates might contain variations in the atpF gene or its regulatory elements. Similar to what has been observed with RecG, where multiple SNPs have been identified across N. meningitidis genomes , genetic variations in atpF could influence protein function and potentially virulence.

• Metabolic adaptation: The ability to adapt to different nutritional environments is crucial for pathogenesis. Strains lacking the metabolic regulator HexR were shown to be deficient in establishing successful bacteremia in an infant rat model of infection , highlighting the connection between metabolism and virulence. Similar correlations might exist for ATP synthase components.

To investigate these relationships, researchers could employ techniques such as:

• RT-qPCR to measure atpF expression in clinical isolates under different conditions

• Proteomics to quantify ATP synthase subunit levels

• Genetic manipulation to create atpF mutants followed by virulence assessment in appropriate models

• Correlation analyses between atpF sequence variations and clinical outcomes

What are the key challenges in studying membrane proteins like ATP synthase in N. meningitidis?

Membrane proteins present unique challenges for researchers, particularly in pathogenic organisms like N. meningitidis:

• Expression and purification difficulties:

  • Low natural expression levels requiring optimization of recombinant systems

  • Tendency to form inclusion bodies during overexpression

  • Requirement for detergents or membrane mimetics to maintain solubility and function

  • Complex purification protocols needed to preserve native structure

• Structural analysis limitations:

  • Challenges in obtaining crystals for X-ray crystallography

  • Requirement for specialized equipment and expertise for cryo-electron microscopy

  • Difficulty in capturing dynamic conformational changes

• Functional assays:

  • Need to reconstruct multi-subunit complexes to assess function

  • Challenges in mimicking the natural membrane environment

  • Difficulty in measuring proton translocation and coupling to ATP synthesis

• Genetic manipulation:

  • Essential nature of ATP synthase making knockout studies difficult

  • Potential polar effects when manipulating genes within operons

  • Need for conditional expression systems

Solutions to these challenges include:

• Using specialized E. coli strains designed for membrane protein expression

• Employing mild detergents or nanodiscs to maintain protein structure

• Developing reconstitution systems in liposomes to assess function

• Using CRISPR interference or antisense RNA approaches for partial gene knockdown

These approaches build upon successful strategies used for other N. meningitidis proteins, such as the expression and purification of transferrin binding proteins and the RecG helicase .

How can researchers effectively study the interaction between atpF and other ATP synthase subunits?

Studying protein-protein interactions within the ATP synthase complex requires specialized approaches:

• Co-expression and co-purification strategies:

  • Design constructs for co-expression of atpF with other subunits

  • Utilize tandem affinity purification tags to isolate intact subcomplexes

  • Employ gradual detergent removal to promote complex assembly

• In vitro binding assays:

  • Surface plasmon resonance (SPR) to measure binding kinetics and affinities

  • Microscale thermophoresis (MST) for interaction studies in solution

  • Pull-down assays with individually purified components

• Structural biology approaches:

  • Cross-linking coupled with mass spectrometry to identify interaction interfaces

  • Cryo-electron microscopy of reconstituted complexes

  • Hydrogen-deuterium exchange mass spectrometry to map binding regions

• Genetic approaches:

  • Bacterial two-hybrid systems adapted for membrane proteins

  • Suppressor mutation analysis to identify functional interactions

  • Site-directed mutagenesis of predicted interaction sites followed by functional assays

These approaches have been successfully applied to study other multi-protein complexes in N. meningitidis and could be adapted for ATP synthase research. For example, techniques used to study DNA binding proteins like RecG could be modified to investigate protein-protein interactions within the ATP synthase complex.

How might ATP synthase function be integrated with other metabolic pathways in N. meningitidis during infection?

ATP synthase function is likely integrated with multiple metabolic pathways that change during the infection process:

• Glucose metabolism: N. meningitidis adapts to glucose availability in human blood through the HexR transcriptional regulator, which controls genes of central carbon metabolism . ATP production through oxidative phosphorylation (involving ATP synthase) would need to be coordinated with glycolysis and the TCA cycle to maintain energy homeostasis under different conditions.

• Iron acquisition: Iron acquisition is crucial for N. meningitidis survival in the host. The transferrin binding proteins (TbpA and TbpB) are important for obtaining iron from human transferrin . The expression and function of these proteins might be coordinated with energy metabolism, as iron is required for many respiratory chain components that generate the proton gradient used by ATP synthase.

• Response to oxidative stress: During infection, N. meningitidis encounters oxidative stress from host immune cells. Adaptation to this stress requires energy for production of defensive enzymes and repair mechanisms, potentially creating increased demand for ATP synthase activity.

• Capsule biosynthesis: The polysaccharide capsule is a key virulence determinant for N. meningitidis . Capsule biosynthesis requires significant energy input, creating a demand for ATP that would involve ATP synthase function.

An integrative systems biology approach combining transcriptomics, proteomics, and metabolomics would be necessary to fully understand these complex interactions. The genome-wide RNA compendium of N. meningitidis provides a foundation for such studies by revealing the organization of the meningococcal transcriptome.

What potential exists for ATP synthase components as vaccine candidates against N. meningitidis?

ATP synthase components could potentially serve as novel vaccine candidates, though several factors would influence their suitability:

• Surface accessibility: The most effective protein vaccine candidates are typically those exposed on the bacterial surface. While ATP synthase is predominantly a membrane protein complex, portions might be accessible to antibodies, particularly in the context of membrane disruption during infection.

• Conservation across strains: Research on transferrin binding proteins has shown that TbpA provides protection against a wider range of meningococcal strains than TbpB alone . Similarly, ATP synthase components that are highly conserved across different N. meningitidis serogroups might provide broad protection.

• Immunogenicity: Effective vaccine antigens must stimulate a robust immune response. Studies would be needed to determine if ATP synthase components are sufficiently immunogenic or require adjuvants or carrier proteins.

• Protection mechanism: Research on TbpA has shown that protection against meningococcal challenge is not always due to complement-mediated lysis, indicating that serum bactericidal activity is not always the most appropriate predictor of efficacy for protein-based meningococcal vaccines . Similar alternative protection mechanisms might apply to ATP synthase-based vaccines.

To evaluate ATP synthase components as vaccine candidates, researchers could:

• Generate recombinant proteins or peptides corresponding to potentially exposed regions

• Assess immunogenicity in animal models

• Evaluate protection in challenge models similar to those used for TbpA and TbpB

• Test for cross-protection against different meningococcal strains

How do post-transcriptional regulatory mechanisms affect atpF expression in N. meningitidis?

The expression of atpF may be subject to sophisticated post-transcriptional regulatory mechanisms:

• sRNA regulation: The genome-wide RNA compendium of N. meningitidis has revealed 65 candidate small RNAs (sRNAs), many of which were validated by northern blot analysis . These sRNAs could potentially regulate atpF mRNA stability or translation.

• Hfq-dependent regulation: Immunoprecipitation with the RNA chaperone Hfq has revealed an unexpectedly large post-transcriptional regulatory network in N. meningitidis, comprising 23 sRNAs and hundreds of potential mRNA targets . If atpF is among these targets, its expression could be modulated through Hfq-dependent mechanisms.

• RNA thermosensors: Many bacteria use RNA thermosensors to regulate gene expression in response to temperature changes. Given that N. meningitidis transitions between environmental temperatures during colonization and invasion, similar mechanisms might regulate ATP synthase components.

• Riboswitches: Metabolite-sensing riboswitches could link atpF expression to the metabolic state of the cell.

Research approaches to investigate these mechanisms could include:

• RNA-seq under different conditions to identify condition-dependent changes in atpF expression

• SHAPE-seq or similar techniques to characterize the secondary structure of the atpF mRNA

• Pull-down assays to identify proteins and sRNAs that interact with atpF mRNA

• Reporter gene assays to map regulatory elements in the atpF untranslated regions

Understanding these regulatory mechanisms could provide insights into how N. meningitidis coordinates energy metabolism with changing environmental conditions during infection.