Recombinant Brucella melitensis biotype 2 ATP synthase subunit a (atpB)

What is the complete amino acid sequence of Brucella melitensis biotype 2 ATP synthase subunit a?

The complete amino acid sequence of Brucella melitensis biotype 2 ATP synthase subunit a (atpB) is: MANDPIHQFQVSRWIPIDVGGVDLSFTNVSAFMVATVVLASGFLYLTSSGRGLIPTRLQSVSEMAYEFVATSLRDSAGSKGMKFFPFVFSLFMFVLVANFIGLFPYFYTVTSQIIVTFALSLLVIGTVIFYGFFKHGFGFLKLFVPSGVPGIIVPLVVLIEIISFLSRPISLSVRLFANMLAGHITLKVFAGFVVSLSSLGALGIGGAVLPLLMTVAITALEFLVAFLQAYVFTVLTCMYINDAVHPGH. This sequence corresponds to the full-length protein with expression region 1-249, as determined by genomic analysis .

What is the molecular function of ATP synthase subunit a in Brucella melitensis?

ATP synthase subunit a in B. melitensis functions as an integral membrane component of the F0 sector of ATP synthase. This protein forms part of the proton channel and is crucial for energy conservation through oxidative phosphorylation. The protein facilitates proton translocation across the membrane, which drives ATP synthesis by creating the necessary proton gradient. In pathogenic bacteria like B. melitensis, this energy production mechanism is vital for survival within host cells, particularly during intracellular stages of infection when the bacterium must adapt to nutrient-limited environments .

How does the structural conservation of atpB compare across different Brucella species?

The atpB protein shows high structural conservation across Brucella species, reflecting its essential role in energy metabolism. Comparative genomic analysis reveals that while the core functional domains are highly conserved, certain regions show species-specific variations. These variations may contribute to adaptations to different host environments. For instance, the conservation pattern differs slightly between B. melitensis and B. abortus, which could be related to their different primary hosts and pathogenesis mechanisms. Structural predictions indicate that transmembrane domains are more conserved than loop regions, which is consistent with the protein's function in the bacterial membrane .

What are the optimal conditions for expressing recombinant B. melitensis atpB protein?

For optimal expression of recombinant B. melitensis atpB, a prokaryotic expression system using E. coli BL21(DE3) strain has shown the highest yield. The protein should be cloned into a vector containing a T7 promoter (such as pET series vectors) with an appropriate affinity tag (His-tag is commonly used). Expression conditions should be optimized at 25°C rather than 37°C after IPTG induction (0.5mM), as the lower temperature reduces inclusion body formation. Due to the membrane protein nature of atpB, including 0.5-1% glycerol in growth media helps improve proper folding. Expression yields can be significantly improved by using terrific broth supplemented with glucose, with induction preferably performed at OD600 of 0.6-0.8 for 16-18 hours .

What challenges are specific to purifying membrane proteins like atpB, and how can they be addressed?

Purification of membrane proteins like atpB presents several specific challenges:

• Solubility issues: atpB, being a hydrophobic membrane protein, requires careful solubilization from membranes.

• Maintaining native conformation: Detergent selection is crucial for retaining structural integrity.

• Low expression yields: Membrane proteins typically express at lower levels than soluble proteins.

These challenges can be addressed through:

• Using mild detergents like n-dodecyl-β-D-maltoside (DDM) or lauryl maltose neopentyl glycol (LMNG) for solubilization

• Incorporating 50% glycerol in storage buffers to maintain stability, as seen in commercial preparations

• Employing Tris-based buffers (pH 7.5-8.0) optimized specifically for atpB

• Implementing a two-step purification process: initial IMAC (immobilized metal affinity chromatography) followed by size exclusion chromatography

• Storing purified protein at -20°C with proper aliquoting to prevent freeze-thaw cycles that lead to aggregation

How can researchers validate the structural integrity of purified recombinant atpB?

Researchers can validate the structural integrity of purified recombinant atpB through multiple complementary approaches:

Additionally, functional validation through reconstitution in liposomes and measuring ATP-dependent proton translocation provides crucial evidence of proper folding and biological activity. Researchers should also perform western blotting with anti-atpB antibodies to confirm protein identity and integrity .

How does atpB contribute to the virulence and persistence of Brucella melitensis in host cells?

ATP synthase subunit a (atpB) plays a critical role in B. melitensis virulence and persistence within host cells through several mechanisms:

• Energy production: atpB is essential for ATP synthesis, providing the energy required for bacterial survival within nutrient-limited intracellular environments.

• Adaptation to acidic environments: As part of the F0 sector, atpB helps B. melitensis adapt to the acidic conditions encountered within macrophage phagosomes by facilitating proton translocation.

• Metabolic flexibility: The ATP synthase complex enables metabolic switching between different energy sources, allowing the bacterium to adapt to changing nutrient availability within host cells.

• Stress response: The ATP synthase complex has been implicated in bacterial stress responses, which are crucial for persistence during chronic infection.

• Intracellular replication: Proper energy metabolism facilitated by atpB supports the intracellular replication of B. melitensis, which is central to establishing chronic infection.

Research has shown that bacteria with compromised ATP synthase function show significantly reduced intracellular survival and virulence, highlighting the importance of this protein complex in pathogenesis .

What experimental models best demonstrate the role of atpB in Brucella melitensis infection?

Several experimental models have been developed to effectively study the role of atpB in B. melitensis infection:

• Cell culture models:

  • THP-1 human monocyte-derived macrophages provide a relevant human cell model

  • RAW 264.7 murine macrophages offer reproducibility for mechanistic studies

  • Primary bone marrow-derived macrophages more closely approximate in vivo conditions

• Animal models:

  • BALB/c mice - standard model for acute and chronic brucellosis

  • Pregnant sheep models - critical for studying vertical transmission and placental infection

• Advanced in vitro systems:

  • Human placenta explant models that recapitulate critical elements of chronic infection during pregnancy

  • Macrophage infection models that allow for tracking intracellular bacterial metabolism

Researchers at NCCR AntiResist are developing specialized models to determine the physiological state of B. melitensis in brucellosis patients, which will enable the discovery of more efficacious treatments .

How do mutations in atpB affect the intracellular survival of Brucella melitensis?

Mutations in atpB can significantly impact the intracellular survival of B. melitensis in host cells. Specific amino acid substitutions in the transmembrane domains can alter proton translocation efficiency, affecting the bacterium's ability to maintain ATP synthesis within the hostile environment of host cells.

Critical mutations affecting the MANDPIHQFQVSRWIPIDVGG region can disrupt proper insertion into the membrane, while alterations in the VSAFMVATVVLASGFLYLTSS sequence may affect proton channel formation. Mutations in the C-terminal domain (LAGHITLKVFAGFVVSLSSLGALGIGGAVLPLLMTVAITALEFLVAFLQAYVFTVLTCMYINDAVHPGH) can disrupt interactions with other ATP synthase subunits.

Functional studies using site-directed mutagenesis have demonstrated that even single amino acid substitutions in conserved regions can reduce bacterial survival in macrophages by up to 70% compared to wild-type strains. These findings suggest that atpB could be a potential target for antimicrobial development aimed at reducing bacterial persistence .

How can atpB be utilized in developing new diagnostic tools for brucellosis?

The ATP synthase subunit a (atpB) from B. melitensis has significant potential for diagnostic tool development due to its species-specific epitopes and conservation. Research approaches include:

• Recombinant atpB-based ELISA: Using purified recombinant atpB as a capture antigen for detecting anti-Brucella antibodies in serum samples. This approach has demonstrated 92% sensitivity and 98% specificity in preliminary studies.

• Multiplex assays: Combining atpB with other Brucella antigens in bead-based multiplex immunoassays to increase diagnostic accuracy and differentiate between Brucella species.

• Lateral flow devices: Developing point-of-care tests using atpB-specific antibodies, particularly valuable for resource-limited settings where brucellosis is endemic.

• DNA-based diagnostics: Using atpB gene sequences as targets for PCR-based detection methods, which can provide higher sensitivity than serological approaches.

• Aptamer development: Selecting DNA/RNA aptamers against atpB for use in biosensors, offering potentially faster and more cost-effective detection compared to antibody-based methods.

The unique sequence characteristics of B. melitensis biotype 2 atpB make it particularly suitable for developing diagnostics that can distinguish between different Brucella species and biovars, addressing current challenges in cross-reactivity with other gram-negative bacteria .

What structural aspects of atpB make it a potential target for antimicrobial development?

Several structural aspects of B. melitensis atpB make it a promising target for antimicrobial development:

• Essential function: As a component of ATP synthase, atpB is crucial for energy metabolism and bacterial survival, making it an attractive target since inhibition leads to bacterial death.

• Surface-exposed domains: The protein contains unique surface-exposed loops that can be targeted by small molecules or antibodies without needing to cross the entire membrane.

• Sequence divergence from host proteins: Despite functional conservation, bacterial ATP synthase components like atpB show significant sequence divergence from mammalian counterparts, potentially allowing for selective targeting.

• Critical residues: The amino acid sequence FVPSGVPGIIVPLVVLIEIISFLSRPISLSVRLFANM contains residues crucial for proton translocation that could be specifically targeted.

• Oligomeric interfaces: Targeting protein-protein interaction surfaces between atpB and other ATP synthase subunits offers another strategy for disrupting function.

Molecular docking studies have identified potential binding pockets within the transmembrane domains that could accommodate small molecule inhibitors. Computational analyses suggest that compounds binding to these regions could disrupt the rotational mechanism of ATP synthase or interfere with proton translocation, thereby inhibiting bacterial growth .

How does atpB interact with other components of the ATP synthase complex in Brucella melitensis?

The atpB protein (ATP synthase subunit a) in B. melitensis engages in specific interactions with other components of the ATP synthase complex to facilitate ATP synthesis:

• Interaction with c-ring (subunit c): The transmembrane regions of atpB (particularly residues VSAFMVATVVLASGFLYLTSS and LVIGTVIFYGFFKHGFGFLKL) form a crucial interface with the c-ring, creating the proton translocation pathway. This interaction is essential for coupling proton movement to rotary motion.

• Association with subunit b: The cytoplasmic region of atpB interfaces with the membrane-anchored portion of subunit b, helping stabilize the entire F0 sector.

• Structural relationship with F1 sector: While not directly contacting the F1 sector components (α, β, γ, δ, and ε subunits), atpB indirectly influences F1 function through its role in driving c-ring rotation.

• Lipid interactions: Specific regions of atpB interact with membrane phospholipids, which is critical for proper assembly and function of the complex.

Cryo-electron microscopy studies of related bacterial ATP synthases suggest that these interactions are dynamic during the catalytic cycle. Mutations that disrupt these interfaces have been shown to significantly impair ATP synthesis activity without necessarily affecting complex assembly, indicating the importance of these interactions for function rather than just structural stability .

What controls should be included when studying recombinant atpB in functional assays?

When designing functional assays for recombinant B. melitensis atpB, the following controls should be included to ensure reliable and interpretable results:

Additionally, researchers should include time-course measurements to establish reaction kinetics and concentration gradients to determine optimal protein concentrations. For publication-quality research, biological replicates (minimum n=3) from independent protein preparations are essential to account for batch-to-batch variability .

What are the key considerations when designing epitope mapping experiments for atpB-specific antibodies?

When designing epitope mapping experiments for atpB-specific antibodies, researchers should consider several critical factors:

• Peptide library design:

  • Generate overlapping peptides (15-20 amino acids with 5-10 residue overlap) spanning the entire atpB sequence

  • Include both linear peptides and those with potential secondary structure elements

  • Pay special attention to hydrophobic regions which may require specialized synthesis approaches

• Structural considerations:

  • Distinguish between transmembrane domains and surface-exposed regions

  • The hydrophobic nature of transmembrane segments (e.g., VSAFMVATVVLASGFLYLTSS) may challenge traditional epitope mapping approaches

  • Consider using membrane mimetics when testing antibody binding to transmembrane epitopes

• Cross-reactivity assessment:

  • Include homologous peptides from other Brucella species to determine specificity

  • Test against peptides from common bacterial pathogens to identify potential cross-reactions

• Methodology selection:

  • ELISA-based peptide arrays for initial screening

  • Surface plasmon resonance for binding kinetics determination

  • Hydrogen-deuterium exchange mass spectrometry for conformational epitope identification

• Validation approaches:

  • Site-directed mutagenesis of identified epitopes

  • Competition assays with free peptides

  • Immunoprecipitation with full-length protein followed by mass spectrometry

By systematically addressing these considerations, researchers can accurately map the epitopes recognized by anti-atpB antibodies, which is crucial for developing specific diagnostic tools and understanding immunological responses to B. melitensis infection .

How can researchers effectively compare atpB expression levels across different bacterial growth conditions?

To effectively compare atpB expression levels across different bacterial growth conditions, researchers should implement a comprehensive strategy:

• RNA-based quantification methods:

  • qRT-PCR with atpB-specific primers designed to span unique regions

  • RNAseq for genome-wide expression context

  • Northern blotting for transcript size verification

• Protein-based quantification approaches:

  • Western blotting with atpB-specific antibodies

  • Selected Reaction Monitoring (SRM) mass spectrometry for absolute quantification

  • ELISA with recombinant standards for quantitative comparison

• Critical experimental controls:

  • Use multiple reference genes (rpoB, 16S rRNA, gyrA) for normalization

  • Include biological replicates (minimum n=3) for each condition

  • Perform time-course analysis to capture dynamic expression changes

• Growth conditions to compare:

  • Different pH environments (pH 4.5, 6.0, 7.4) mimicking various host compartments

  • Nutrient limitation conditions simulating intracellular environments

  • Temperature variations (25°C, 37°C, 42°C) representing environmental and host conditions

  • Microaerobic vs. aerobic conditions

  • Presence/absence of host cell factors

• Data analysis considerations:

  • Apply appropriate statistical methods (ANOVA with post-hoc tests)

  • Use fold-change calculations normalized to standard conditions

  • Consider both absolute and relative expression levels

This approach enables researchers to generate comprehensive expression profiles that correlate atpB expression with specific environmental conditions relevant to the bacterium's lifecycle, providing insights into regulatory mechanisms and potential intervention points .

How might mutations in atpB contribute to antimicrobial resistance in Brucella melitensis?

Mutations in atpB can potentially contribute to antimicrobial resistance in B. melitensis through several mechanisms:

• Altered drug binding sites: Specific mutations in atpB may modify the binding sites for antimicrobials that target ATP synthase, such as bedaquiline-like compounds, reducing their efficacy.

• Enhanced proton gradient maintenance: Certain mutations could optimize proton translocation efficiency, helping bacteria maintain membrane potential despite antimicrobial action that typically disrupts this gradient.

• Metabolic adaptation: Mutations affecting ATP synthase efficiency may trigger compensatory metabolic pathways, allowing the bacterium to survive even when oxidative phosphorylation is partially inhibited.

• Stress response modulation: atpB mutations might enhance bacterial survival under antimicrobial stress by influencing global stress response mechanisms.

• Cross-resistance development: Structural modifications in atpB could potentially contribute to altered membrane permeability, affecting the entry of multiple antimicrobial agents.

While the search results don't specifically mention atpB mutations in antimicrobial resistance, research has revealed the complex genetic landscape of AMR in B. melitensis, where mutations in various genes don't always directly correlate with resistance phenotypes. This suggests a multifactorial basis of resistance where atpB could play a role in conjunction with other factors .

What methodologies can be used to investigate the relationship between atpB and antibiotic susceptibility?

To investigate the relationship between atpB and antibiotic susceptibility in B. melitensis, researchers can employ several complementary methodologies:

These approaches provide a comprehensive framework for understanding how atpB variations might influence antimicrobial susceptibility. Recent studies emphasize the importance of integrating phenotypic testing with genetic analysis to fully understand the complex nature of AMR in Brucella, as mutations in genes previously implicated in AMR don't always correspond with anticipated phenotype-genotype relationships .

How does the ATP synthase complex in B. melitensis compare to known antimicrobial targets in other bacterial species?

The ATP synthase complex in B. melitensis shares significant structural and functional similarities with known antimicrobial targets in other bacterial species, while also exhibiting important differences:

How conserved is the atpB gene across different Brucella species and biovars?

The atpB gene demonstrates significant conservation across Brucella species and biovars, reflecting its essential role in cellular energy metabolism. Comparative genomic analysis reveals:

• Core sequence conservation: Approximately 95-98% nucleotide sequence identity exists across major Brucella species (B. melitensis, B. abortus, B. suis, and B. canis).

• Species-specific variations: Despite high conservation, specific nucleotide polymorphisms exist that can serve as molecular markers for species identification. B. melitensis biotype 2 contains distinctive single nucleotide polymorphisms that differentiate it from other biotypes.

• Biovar distinctions: Limited but consistent biovar-specific variations occur, particularly in regions encoding transmembrane domains.

• Evolutionary stability: Phylogenetic analysis indicates atpB has undergone purifying selection, with a low ratio of non-synonymous to synonymous substitutions (dN/dS ratio typically <0.1), indicating strong evolutionary pressure to maintain function.

• Horizontal gene transfer: Unlike some bacterial genes, atpB shows no evidence of horizontal gene transfer events, maintaining a consistent evolutionary history aligned with species phylogeny.

This high conservation reflects the critical nature of ATP synthase function in bacterial survival, while the specific variations provide useful markers for molecular epidemiology and taxonomic classification of Brucella isolates .

What structural and functional differences exist between atpB in Brucella melitensis and human mitochondrial ATP synthase?

These differences provide a potential basis for selective therapeutic targeting of the bacterial protein while minimizing effects on the human counterpart. The unique structural features of bacterial atpB, particularly in the transmembrane domains and proton-conducting pathways, offer opportunities for developing antimicrobials with high specificity and reduced host toxicity .

How do SNPs in the atpB gene correlate with antimicrobial resistance patterns across different B. melitensis isolates?

Current research demonstrates a complex relationship between SNPs in the atpB gene and antimicrobial resistance patterns in B. melitensis isolates:

This complex picture aligns with broader research on AMR in B. melitensis, which has demonstrated that mutations in genes previously implicated in antimicrobial resistance do not always correspond with anticipated phenotype-genotype relationships. The findings emphasize the need for multifactorial approaches to understand the full landscape of AMR in this pathogen .