Recombinant Brucella ovis ATP synthase subunit a (atpB)

What is Brucella ovis ATP synthase subunit a (atpB) and what is its significance in research?

ATP synthase subunit a (atpB) is a protein encoded by the atpB gene (BOV_0394) in Brucella ovis, a veterinary pathogen that causes epididymitis in sheep but, unlike other Brucella species, does not cause zoonotic disease in humans . The protein is recommended to be named "ATP synthase subunit a" with alternative names including "ATP synthase F0 sector subunit a" and "F-ATPase subunit 6" .

The significance of this protein in research stems from its role in energy metabolism and its potential as a target for vaccine development against brucellosis. As part of the ATP synthase complex, atpB is involved in ATP synthesis, which is crucial for bacterial survival. The protein's conservation among Brucella species yet specific sequence variations in B. ovis makes it valuable for studying host specificity and pathogenesis mechanisms . Research on this protein contributes to understanding the reduced virulence of B. ovis compared to zoonotic Brucella species.

How does the genomic context of B. ovis atpB compare to other Brucella species?

The genomic context of atpB in B. ovis shows notable similarities and differences when compared to other Brucella species. The gene is located on Chromosome I of B. ovis (designated as BOV_0394 in the ordered locus names) . While the atpB gene itself is highly conserved among Brucella species with over 94% identity at the nucleotide level, the genomic environment shows species-specific differences .

B. ovis has undergone significant genome degradation compared to zoonotic Brucella species, with a higher percentage of pseudogenes. Specifically, Chromosome I of B. ovis contains 119 pseudogenes (5.8% of genes) compared to 61 (2.8%) in B. suis, 186 (8.5%) in B. abortus, and 83 (3.8%) in B. melitensis . This genomic degradation is thought to contribute to the narrowed host range and reduced virulence of B. ovis.

The table below summarizes the genomic comparison between B. ovis and other Brucella species:

What are the optimal storage and handling conditions for recombinant B. ovis atpB?

Recombinant B. ovis ATP synthase subunit a (atpB) requires specific storage and handling conditions to maintain its stability and functionality. Based on standard protocols for this protein, the following conditions are recommended:

Storage buffer: The protein should be stored in a Tris-based buffer with 50% glycerol, specifically optimized for this protein's stability . The glycerol acts as a cryoprotectant to prevent damage during freeze-thaw cycles.

Temperature conditions: For short-term storage, working aliquots should be kept at 4°C for up to one week. For extended storage, the protein should be kept at -20°C, while long-term archival storage is best at -80°C .

Handling precautions: Repeated freezing and thawing should be avoided as this can lead to protein denaturation and loss of activity . It is advisable to prepare small aliquots during initial processing to minimize freeze-thaw cycles.

When preparing the protein for experimental use, gentle thawing on ice is recommended, followed by brief centrifugation to collect the sample at the bottom of the tube. For applications requiring buffer exchange, methods such as dialysis or size-exclusion chromatography should be performed at 4°C to maintain protein stability.

What experimental approaches have been used for developing recombinant vaccines using B. ovis proteins?

Recombinant vaccine development using B. ovis proteins has employed several sophisticated experimental approaches, with particular success using chimeric protein strategies. One notable approach involves using Brucella lumazine synthase (BLS) as a scaffold protein decorated with protective epitopes from outer membrane proteins .

The most successful experimental approach documented involved:

• Identification of protective epitopes: Researchers identified a protective epitope derived from an outer membrane protein (Omp31) from Brucella species .

• Chimeric protein design: A chimeric protein was designed with BLS as a scaffold decorated with 10 copies of the Omp31 protective epitope. This design exploits the decameric arrangement and remarkable stability of BLS, enhancing the immunogenicity of the inserted epitopes .

• Recombinant protein expression: The chimeric construct (rBLSOmp31) was expressed as a recombinant protein in a suitable expression system .

• Immunization and challenge studies: BALB/c mice were vaccinated with:

  • The chimeric protein (rBLSOmp31)

  • Co-delivery of separate recombinant proteins (rBLS + rOmp31)

  • Control vaccine (B. melitensis strain Rev.1)

• Immune response analysis: Researchers evaluated:

  • Humoral immune response against the inserted peptide

  • T helper 1 (Th1) response specific to both the peptide and BLS

  • Cytotoxic T cell responses

• Protection assessment: Vaccinated animals were challenged with B. ovis and B. melitensis to evaluate protection efficacy .

Results showed that the chimeric rBLSOmp31 provided superior protection against B. ovis compared to co-delivery of the separate proteins (rBLS + rOmp31) and similar protection to the commercial Rev.1 vaccine. The chimera also provided protection against B. melitensis, though to a lesser degree than Rev.1 . This experimental approach demonstrates the potential of using B. ovis proteins in subunit vaccines that can elicit humoral, T helper, and cytotoxic immune responses.

How does genomic degradation in B. ovis affect protein expression compared to zoonotic Brucella species?

The genomic degradation observed in B. ovis has significant implications for its protein expression profile compared to zoonotic Brucella species. This phenomenon affects not only atpB but the entire proteome, contributing to the organism's host specificity and reduced virulence.

Comparative genomic analysis reveals several key patterns affecting protein expression:

• Pseudogene accumulation: B. ovis has a higher percentage of pseudogenes compared to B. suis (11.5% vs. 0.1% on Chromosome II), indicating extensive gene inactivation . These pseudogenes may encode non-functional proteins or no protein at all, reducing the functional proteome.

• Loss of key virulence factors: B. ovis lacks genomic island 2, which encodes functions required for lipopolysaccharide biosynthesis. This includes the absence of the wboA glycosyl transferase gene and a second glycosyl transferase, contributing to the rough LPS phenotype of B. ovis .

• Inactivation of metabolic pathways: Genes encoding urease, nutrient uptake, and utilization systems are inactivated in B. ovis . This affects the expression of proteins involved in metabolism and nutrient acquisition, potentially limiting the bacterium's ability to survive in diverse environments.

• Increased presence of insertion sequences: B. ovis has substantially more copies of insertion element IS711 (25 copies on Chromosome I compared to 5 in other Brucella species) . These mobile genetic elements can disrupt gene expression and regulation.

• Deletion of transport systems: The 44.5 kb island containing four predicted ABC transport systems in B. suis is absent from the B. ovis genome . This reduces the expression of membrane transport proteins that may be important for virulence.

What immunological responses are elicited by recombinant B. ovis proteins in animal models?

Recombinant B. ovis proteins, particularly when used in chimeric vaccine constructs, elicit a complex and multifaceted immunological response in animal models. Based on experimental data, these responses include:

• Humoral immune response: Vaccination with recombinant B. ovis proteins, such as the rBLSOmp31 chimeric construct, induces a strong antibody response against the inserted peptide epitopes . These antibodies can recognize native bacterial proteins and potentially neutralize their function or mark bacteria for clearance by phagocytes.

• T helper 1 (Th1) response: Recombinant B. ovis protein constructs stimulate a robust Th1 immune response, characterized by the production of cytokines like IFN-γ, TNF-α, and IL-2 . This Th1 response is critical for controlling intracellular bacterial infections like brucellosis by activating macrophages to destroy internalized bacteria.

• Cytotoxic T lymphocyte (CTL) response: Animal models vaccinated with recombinant B. ovis proteins show evidence of cytotoxic T cell activation . These CTLs can directly kill host cells infected with Brucella, preventing bacterial replication and spread.

• Memory immune response: The immunological response to recombinant B. ovis proteins includes the development of immunological memory, which is essential for long-term protection against challenge infections.

• Cross-protective immunity: In some cases, recombinant B. ovis proteins can elicit immune responses that provide cross-protection against related Brucella species. For example, the rBLSOmp31 chimera induced protection not only against B. ovis but also against B. melitensis .

The effectiveness of these immune responses in providing protection varies depending on the specific recombinant construct and the challenge strain. For instance, the rBLSOmp31 chimera provided better protection against B. ovis than against B. melitensis, indicating that the immune response elicited is more effective against the homologous strain .

What methods can be used to optimize expression and purification of recombinant B. ovis atpB?

Optimizing the expression and purification of recombinant B. ovis ATP synthase subunit a (atpB) presents several challenges due to its hydrophobic nature as a membrane protein. The following methodological approaches can be employed to enhance expression and purification:

• Expression system selection:

  • Bacterial systems: Modified E. coli strains like C41(DE3) or C43(DE3) that are specifically designed for membrane protein expression

  • Cell-free expression systems for toxic membrane proteins

  • Baculovirus-insect cell systems for complex membrane proteins requiring eukaryotic machinery

• Vector optimization:

  • Use of strong inducible promoters with tight regulation (T7, tac)

  • Incorporation of fusion tags that enhance solubility (MBP, SUMO, Trx)

  • Codon optimization for the expression host

  • Integration of signal sequences for proper membrane targeting

• Expression conditions optimization:

  • Reduced temperature (16-25°C) during induction to slow protein production and allow proper folding

  • Lower inducer concentrations to prevent formation of inclusion bodies

  • Supplementation with specific lipids that stabilize membrane proteins

  • Addition of membrane protein-specific chaperones

• Membrane protein extraction:

  • Careful selection of detergents (DDM, LDAO, or CHAPS) for membrane solubilization

  • Optimization of detergent concentration and solubilization time

  • Two-phase extraction systems for initial enrichment

• Purification strategies:

  • Immobilized metal affinity chromatography (IMAC) using His-tags

  • Size exclusion chromatography for removing aggregates and detergent micelles

  • Ion exchange chromatography as a polishing step

  • Detergent exchange during purification to improve protein stability

• Stability enhancement:

  • Addition of lipids or cholesterol to mimic native membrane environment

  • Use of detergent-stable buffers with optimized pH and ionic strength

  • Storage in glycerol-containing buffers (typically 50%) as used for commercial preparations

  • Addition of specific stabilizing agents like arginine or trehalose

• Quality assessment:

  • Circular dichroism spectroscopy to verify secondary structure

  • Size exclusion chromatography with multi-angle light scattering (SEC-MALS) to assess oligomeric state

  • Functional assays to confirm biological activity

  • Negative stain electron microscopy to visualize protein integrity

When developing expression protocols specifically for B. ovis atpB, it's important to consider that this protein naturally exists as part of a multi-subunit complex. Co-expression with interacting partners from the ATP synthase complex may improve folding and stability of the recombinant protein.

How can recombinant B. ovis atpB be utilized in diagnostic applications for brucellosis?

Recombinant B. ovis ATP synthase subunit a (atpB) offers significant potential for developing advanced diagnostic applications for brucellosis, particularly for differentiating B. ovis infections from other Brucella species. Several methodological approaches can be implemented:

• Enzyme-Linked Immunosorbent Assays (ELISAs):

  • Indirect ELISA: Recombinant B. ovis atpB can be immobilized on microplates to detect anti-atpB antibodies in sheep sera . This approach allows for high-throughput screening of large flocks.

  • Competitive ELISA: Using labeled monoclonal antibodies specific to B. ovis atpB epitopes to compete with serum antibodies, providing higher specificity than indirect methods.

  • Sandwich ELISA: For detecting atpB antigen directly in clinical samples, utilizing capture and detection antibodies specific to different epitopes of the protein.

• Lateral Flow Immunoassays:

  • Development of field-deployable rapid tests using recombinant atpB for point-of-care diagnostics in veterinary settings.

  • Multiplexed assays incorporating multiple B. ovis antigens including atpB for improved sensitivity.

• Serological Differentiation:

  • Using specific epitopes of atpB that differ between B. ovis and zoonotic Brucella species to develop differential diagnostic tests.

  • Implementation of protein microarrays containing atpB along with other species-specific antigens to generate serological profiles distinctive to B. ovis infections.

• Molecular Diagnostic Applications:

  • Development of PCR primers targeting the atpB gene region specific to B. ovis.

  • The genomic context of atpB can be utilized, particularly considering that B. ovis has a 26.5 kb region on Chromosome II that is absent from human pathogenic Brucella genomes but present in all tested B. ovis isolates . This region could serve as a molecular marker for species identification.

• Next-Generation Approaches:

  • Mass spectrometry-based identification of atpB peptides in clinical samples for rapid and accurate diagnosis.

  • Development of aptamer-based biosensors targeting B. ovis atpB for highly sensitive detection.

  • Implementation of CRISPR-Cas diagnostic systems for sequence-specific detection of B. ovis atpB gene variants.

• Validation Methodologies:

  • Cross-reactivity testing against other Brucella species and common bacterial pathogens of sheep.

  • Determination of sensitivity and specificity using panels of well-characterized positive and negative field samples.

  • Evaluation of diagnostic performance in different stages of infection (acute vs. chronic).

The development of diagnostics based on recombinant B. ovis atpB should consider the genomic differences between B. ovis and zoonotic Brucella species, potentially focusing on regions that differentiate B. ovis from B. ceti, as some genomic regions are shared between these two species but absent in human pathogenic strains .