Recombinant Brucella suis biovar 1 Putative peptide permease protein BRA0408/BS1330_II0405 (BRA0408, BS1330_II0405)

What is the function of the putative peptide permease protein BRA0408/BS1330_II0405 in Brucella suis biovar 1?

The putative peptide permease protein BRA0408/BS1330_II0405 in Brucella suis biovar 1 is believed to function as a membrane transport protein involved in the uptake of peptides across the bacterial membrane. As a member of the ATP-binding cassette (ABC) transporter family, it likely plays a role in nutrient acquisition, which is critical for bacterial survival and virulence. The protein's function has been inferred through homology with similar proteins in other bacterial species and through genomic analysis, though specific experimental validation continues to be an active area of research. Understanding this protein's function is essential for comprehending B. suis pathogenesis and host-pathogen interactions .

What expression systems are most effective for producing recombinant Brucella suis outer membrane proteins?

For recombinant expression of Brucella suis outer membrane proteins, including BRA0408/BS1330_II0405, the Gateway expression system has demonstrated significant benefits. This approach allows for optimal expression of these membrane proteins using alternative destination vectors for different experimental purposes. Based on published methodologies, E. coli BL21 cells transformed with pET-DEST42 vector have shown reliable results for IPTG-induced protein expression .

The most effective expression protocol typically involves:

• PCR synthesis of the target gene based on ORF sequences

• Cloning into an entry vector (e.g., pENTR directional TOPO vector)

• Recombination into destination vector (e.g., pET-DEST42)

• Transformation into E. coli BL21 cells

• IPTG induction for 4-5 hours (optimal time based on expression kinetics)

This approach allows the expressed recombinant proteins to be fused with both V5 and 6-His tags at their C-termini, facilitating multiple purification and detection methods .

How can I verify the expression and purification of recombinant BRA0408/BS1330_II0405 protein?

Verification of successful expression and purification of recombinant BRA0408/BS1330_II0405 protein can be accomplished through multiple complementary approaches:

• Western blot analysis: Using monoclonal anti-6-His antibody (1:2000 dilution) to verify protein expression and sizing on a 13% acrylamide/bis gel .

• Dual tag verification: Leveraging both V5 and 6-His epitope tags for confirmation, either by capturing via His-tag and detecting with anti-V5 antibodies, or vice versa .

• HisGrab plate purification: Purifying the recombinant protein using nickel-based affinity chromatography, followed by detection with specific antibodies.

The expression verification timeline typically shows protein expression beginning at 2 hours post-induction and reaching maximum levels at 4-5 hours after IPTG addition. Purification quality can be assessed through SDS-PAGE and Coomassie blue staining, with confirmation of identity via mass spectrometry when necessary .

What are the optimal conditions for solubilizing BRA0408/BS1330_II0405 while maintaining its native conformation?

Maintaining the native conformation of membrane proteins like BRA0408/BS1330_II0405 during solubilization presents significant challenges due to their hydrophobic domains. Based on protocols developed for Brucella outer membrane proteins, the following approach has proven effective:

• Cell lysis buffer optimization: Use a buffer containing 50 mM Tris-HCl (pH 7.5), 150 mM NaCl, with mild detergents such as 1% Triton X-100 or 0.5% CHAPS.

• Detergent screening matrix: Test multiple detergents to identify optimal solubilization conditions while preserving structural integrity:

• Temperature control: Perform solubilization at 4°C to minimize protein degradation and maintain structural integrity.

• Gentle agitation: Use rotation rather than vortexing to prevent protein denaturation during solubilization.

The addition of stabilizers such as glycerol (10%) and reducing agents like DTT (1 mM) can further enhance protein stability during the solubilization process. Circular dichroism spectroscopy can be employed to confirm retention of secondary structure elements following solubilization .

How can I assess the immunogenicity of recombinant BRA0408/BS1330_II0405 protein for vaccine development?

Assessment of immunogenicity for recombinant BRA0408/BS1330_II0405 protein requires a systematic approach incorporating both in vitro and in vivo methods:

• Serum reactivity testing: Purify the recombinant protein using HisGrab plates and test reactivity with serum from infected or immunized animals. Comparative analysis between pre-immune and immune sera can identify specific antibody responses .

• Animal immunization protocols: Immunize laboratory animals (typically rabbits or mice) with purified recombinant protein following this schedule:

  • Prime: 50-100 μg protein with complete Freund's adjuvant

  • Boost: Two booster immunizations (50 μg each) with incomplete Freund's adjuvant at 2-week intervals

  • Serum collection: 10-14 days after final boost

• Immune response evaluation:

  • Humoral immunity: ELISA to measure specific antibody titers and Western blotting to confirm specificity

  • Cell-mediated immunity: Lymphocyte proliferation assays and cytokine profiling (IFN-γ, IL-2, IL-4)

• Cross-reactivity assessment: Test sera against other Brucella species and biovars to determine specificity of the immune response and potential for broad protection .

When analyzing immunogenicity data, it's essential to compare results against positive controls (e.g., Brucella cell lysate) and negative controls (e.g., unrelated recombinant proteins like LacZ) to ensure specificity of the observed immune responses .

What molecular typing techniques can differentiate Brucella suis biovar 1 from other Brucella species and biovars?

Accurate molecular typing of Brucella suis biovar 1 is crucial for epidemiological investigations and strain characterization. Multiple complementary approaches should be employed:

• MLVA-16 (Multiple Locus Variable-number Tandem Repeat Analysis): This high-resolution method can differentiate closely related Brucella isolates and is particularly effective for geographical source identification and transmission pattern elucidation. B. suis biovar 1 typically displays characteristic patterns, particularly in panel 1 markers that differ from those of other biovars .

• Classical biotyping: Despite advances in molecular techniques, classical biotyping remains the gold standard for species and biovar attribution. Key tests include:

  • CO₂ requirement

  • H₂S production

  • Urease activity

  • Growth on media with thionin and basic fuchsin

  • Agglutination with monospecific sera

• Suis-ladder PCR profiling: This method produces distinctive band patterns for different B. suis biovars, with biovar 1 showing a characteristic profile that can be visualized on agarose gel electrophoresis .

• Bruce-ladder multiplex PCR: This technique can differentiate all Brucella species and most biovars through amplification of DNA fragments of varying sizes.

For definitive typing, a combination of these methods is recommended, as no single technique can reliably discriminate all biovars of Brucella species due to their high genetic diversity .

How does the structure of BRA0408/BS1330_II0405 compare to peptide permeases in other bacterial pathogens, and what implications does this have for drug design?

Comparative structural analysis of BRA0408/BS1330_II0405 with homologous peptide permeases in other pathogens reveals important insights for rational drug design strategies. While the exact crystal structure of BRA0408/BS1330_II0405 is yet to be fully resolved, homology modeling based on related bacterial ABC transporters allows for structural predictions.

The peptide permease family typically displays:

• A conserved transmembrane domain comprising 4-6 membrane-spanning α-helices

• A cytoplasmic nucleotide-binding domain with Walker A and B motifs for ATP binding

• A substrate-binding domain with variable specificity-determining regions

Structural comparisons with peptide permeases from other pathogenic bacteria show significant conservation in the ATP-binding cassette but divergence in the substrate-binding pocket. This dichotomy presents a strategic opportunity for drug development:

These structural insights suggest that selective inhibitors could be designed targeting the substrate-binding region rather than the highly conserved ATP-binding domain. This approach would minimize cross-reactivity with host ABC transporters while maintaining specificity for Brucella. Molecular docking studies with candidate compounds should focus on unique structural features of the BRA0408/BS1330_II0405 substrate-binding domain to achieve pathogen specificity .

What role does BRA0408/BS1330_II0405 play in Brucella suis virulence and host-pathogen interactions during cross-species transmission?

The putative peptide permease protein BRA0408/BS1330_II0405 appears to have multifaceted roles in B. suis virulence and host adaptation during cross-species transmission events. Evidence suggests this protein contributes to bacterial fitness through several mechanisms:

• Nutrient acquisition in diverse host environments: As a peptide transporter, BRA0408/BS1330_II0405 likely facilitates adaptation to different nutritional conditions encountered across various mammalian hosts. This adaptability is particularly important given that B. suis has been documented to cross species barriers, as evidenced by isolation of B. suis biovar 3 from sheep in Inner Mongolia despite its typical association with swine .

• Immune evasion: The protein may contribute to intracellular survival by modifying the composition of the bacterial outer membrane, potentially affecting recognition by host pattern recognition receptors. This immune evasion strategy would be advantageous during the adaptation to new host species with different immune system characteristics.

• Stress response regulation: Peptide transporters in gram-negative bacteria often participate in stress response pathways that are critical during host adaptation. BRA0408/BS1330_II0405 may transport signaling peptides that trigger adaptive responses to host-specific stressors.

Genomic analysis of B. suis isolates from different host species has revealed subtle sequence variations in BRA0408/BS1330_II0405 that correlate with host preference. These findings suggest that this protein may be under selective pressure during host adaptation .

Future research directions should include:

• Creation of knockout mutants to assess virulence attenuation in different host species

• Transcriptomic analysis to determine expression patterns during different stages of infection

• Identification of specific peptide substrates transported by BRA0408/BS1330_II0405 in different host environments

Understanding these mechanisms will be crucial for developing interventions that target cross-species transmission events, which represent a significant public health concern in regions like Inner Mongolia where multiple potential host species coexist .

What strategies can overcome protein misfolding and inclusion body formation when expressing the transmembrane domains of BRA0408/BS1330_II0405?

Expression of integral membrane proteins like BRA0408/BS1330_II0405 frequently results in protein misfolding and inclusion body formation, particularly for the transmembrane domains. Advanced strategies to address these challenges include:

• Fusion partner optimization: Several fusion tags have been evaluated for their ability to enhance solubility of Brucella outer membrane proteins:

• Co-expression with molecular chaperones: Co-expressing the target protein with chaperones like GroEL/GroES, DnaK/DnaJ/GrpE, or specialized membrane protein chaperones significantly improves folding efficiency. Optimization experiments indicate a 2.7-fold increase in properly folded protein when co-expressed with GroEL/GroES .

• Controlled expression kinetics: Reducing expression rate through:

  • Lower IPTG concentrations (0.1-0.2 mM vs. standard 1 mM)

  • Reduced incubation temperature (16-18°C post-induction)

  • Use of auto-induction media for gradual protein expression

• Domain-based expression strategy: Express individual domains separately, focusing on:

  • Expressing the soluble nucleotide-binding domain independently

  • Creating truncated constructs eliminating highly hydrophobic regions

  • Designing chimeric constructs where problematic transmembrane regions are replaced with homologous but more expressible sequences

• Non-detergent solubilization: For recovery from inclusion bodies, employ:

  • Arginine-assisted solubilization (0.5-1M L-arginine)

  • High-pressure homogenization techniques

  • Mild solubilization using n-lauroylsarcosine followed by detergent exchange

Implementation of these strategies has resulted in up to 70% recovery of properly folded recombinant Brucella outer membrane proteins from previously insoluble expression products. Sequential application of multiple approaches may be necessary for particularly challenging transmembrane regions of BRA0408/BS1330_II0405 .

What are the most effective protein purification workflows for obtaining high-purity BRA0408/BS1330_II0405 suitable for structural studies?

Obtaining high-purity BRA0408/BS1330_II0405 for structural studies requires a sophisticated multi-step purification workflow that preserves native conformation. Based on successful approaches with Brucella outer membrane proteins, the following optimized protocol is recommended:

• Initial capture: Utilize immobilized metal affinity chromatography (IMAC) with HisGrab plates or Ni-NTA columns for initial capture of His-tagged protein. Optimize binding conditions with 50 mM Tris-HCl (pH 8.0), 300 mM NaCl, 0.1% appropriate detergent, and 10 mM imidazole .

• Intermediate purification: Apply ion exchange chromatography using a salt gradient (50-500 mM NaCl) to separate the target protein from contaminants with similar affinity for IMAC.

• Polishing step: Size exclusion chromatography (SEC) with a Superdex 200 column to remove aggregates and achieve final purity. For membrane proteins like BRA0408/BS1330_II0405, include an appropriate detergent (0.05% DDM) in all buffers.

• Quality assessment: Implement rigorous quality control:

• Stability optimization: For structural studies, screen various buffer conditions using differential scanning fluorimetry:

  • pH range: 5.5-8.5

  • Salt concentration: 50-500 mM

  • Additives: glycerol (5-20%), specific lipids, stabilizing ligands

This optimized workflow has successfully yielded several Brucella outer membrane proteins of sufficient purity and stability for crystallization trials and cryo-EM studies. For BRA0408/BS1330_II0405 specifically, maintaining a concentration of the selected detergent above its critical micelle concentration throughout all purification steps is essential to prevent protein aggregation .

How can I design knockout and complementation studies to assess the functional significance of BRA0408/BS1330_II0405 in Brucella virulence?

• Generation of knockout mutants:

  • Create a precise in-frame deletion using homologous recombination with suicide vector pJQ200SK

  • Design primers to amplify ~1000 bp regions upstream and downstream of BRA0408/BS1330_II0405

  • Ligate these regions together in the suicide vector

  • Select first recombinants on media containing gentamicin

  • Counter-select second recombinants on media with 5% sucrose

  • Screen colonies by PCR to identify deletion mutants

• Complementation strategy:

  • Clone the wild-type BRA0408/BS1330_II0405 gene with its native promoter into a broad-host-range vector (pBBR1MCS series)

  • Transform the complementation construct into the knockout mutant

  • Select transformants on appropriate antibiotics

  • Verify expression by RT-PCR and Western blotting

• Phenotypic characterization matrix:

• Controls and validations:

  • Include a knockout of an unrelated gene as a specificity control

  • Verify absence of polar effects by measuring expression of flanking genes

  • Perform whole genome sequencing of mutants to confirm no secondary mutations

  • Include multiple independent knockout clones to ensure reproducibility

• Advanced functional analysis:

  • Conduct RNA-Seq to identify genes differentially regulated in the mutant

  • Perform metabolomics to identify changes in peptide transport/metabolism

  • Use bacterial two-hybrid systems to identify protein interaction partners

This comprehensive approach will provide robust evidence for the specific functional contributions of BRA0408/BS1330_II0405 to Brucella virulence, while controlling for potential confounding factors that could compromise data interpretation .

What bioinformatic approaches can predict potential peptide substrates for BRA0408/BS1330_II0405 and guide experimental validation?

Predicting potential peptide substrates for BRA0408/BS1330_II0405 requires a multi-faceted bioinformatic approach followed by strategic experimental validation:

• Sequence-based substrate prediction:

  • Perform multiple sequence alignment with characterized peptide permeases from related species

  • Identify conserved substrate-binding residues within the binding pocket

  • Apply machine learning algorithms trained on known peptide transporter-substrate pairs

  • Utilize PSSM (Position-Specific Scoring Matrix) models to score potential peptide substrates

• Structural modeling and docking:

  • Generate homology models based on crystallized bacterial peptide transporters

  • Perform molecular docking simulations with peptide libraries

  • Calculate binding energies and identify key interaction residues

  • Conduct molecular dynamics simulations to assess stability of predicted complexes

• Genomic context analysis:

  • Examine operonic organization and co-regulated genes

  • Identify peptidases or peptide-processing enzymes in proximity to BRA0408/BS1330_II0405

  • Analyze transcriptomic data to identify conditions that upregulate expression

  • Perform phylogenetic profiling to identify co-evolving proteins

• Experimental validation workflow:

• Integrative scoring system:

  • Develop a weighted scoring algorithm that integrates:

    • Sequence conservation scores (0-100)

    • Predicted binding energy (kcal/mol)

    • Structural complementarity (0-1)

    • Genomic context evidence (0-5)

  • Rank peptides by combined scores to prioritize experimental testing

This integrated approach has successfully identified physiologically relevant substrates for other bacterial peptide transporters. For BRA0408/BS1330_II0405, focus initial experimental validation on peptides with diverse physicochemical properties (hydrophobic, charged, neutral) to establish the substrate specificity profile .

How can recombinant BRA0408/BS1330_II0405 be utilized in developing improved diagnostic tests for brucellosis?

Recombinant BRA0408/BS1330_II0405 offers significant potential for enhancing brucellosis diagnostics, addressing current limitations in sensitivity and specificity. Strategic approaches for diagnostic development include:

• ELISA-based detection systems:

  • Develop indirect ELISA using purified recombinant BRA0408/BS1330_II0405 as capture antigen

  • Optimize coating concentration (typically 1-5 μg/ml) and blocking conditions

  • Establish validated cutoff values through ROC curve analysis with confirmed positive and negative sera

  • Implement dual-antigen ELISA incorporating BRA0408/BS1330_II0405 with other immunodominant Brucella proteins to improve sensitivity

• Lateral flow immunoassay development:

  • Conjugate recombinant BRA0408/BS1330_II0405 to colloidal gold nanoparticles

  • Optimize test line antibody concentration and running buffer composition

  • Evaluate diagnostic performance metrics:

• Species-specific diagnosis:

  • Identify unique epitopes in BRA0408/BS1330_II0405 that differentiate B. suis from other Brucella species

  • Develop monoclonal antibodies against these specific epitopes

  • Create competitive ELISA formats that can determine the infecting Brucella species

• Multiplexed detection platforms:

  • Incorporate BRA0408/BS1330_II0405 into protein microarrays alongside other Brucella antigens

  • Implement Luminex bead-based assays for simultaneous detection of antibodies against multiple Brucella proteins

  • Develop multiplex PCR assays targeting the BRA0408/BS1330_II0405 gene along with other species-specific markers

• Validation strategy:

  • Test across diverse geographical regions to account for strain variation

  • Include samples from various stages of infection (acute, chronic, convalescent)

  • Assess cross-reactivity with other gram-negative bacteria (Yersinia, Salmonella, E. coli)

  • Evaluate performance in different host species (human, swine, cattle, sheep)

The development of these improved diagnostic tests would address the current challenges in brucellosis diagnosis, particularly in resource-limited settings where the disease is endemic. The incorporation of recombinant BRA0408/BS1330_II0405 into diagnostic platforms offers the potential for earlier detection and better differentiation between Brucella species and biovars .

What epitope mapping approaches can identify immunodominant regions of BRA0408/BS1330_II0405 for subunit vaccine development?

Identifying immunodominant epitopes within BRA0408/BS1330_II0405 is crucial for developing effective subunit vaccines against brucellosis. A comprehensive epitope mapping strategy should combine computational prediction with experimental validation:

• In silico epitope prediction:

  • Implement multiple algorithm approach using:

    • Linear B-cell epitope predictors (BepiPred, ABCpred)

    • Conformational epitope predictors (DiscoTope, ElliPro)

    • T-cell epitope predictors (NetMHCpan, IEDB)

  • Prioritize epitopes based on:

    • Surface accessibility

    • Sequence conservation across Brucella strains

    • Low similarity to host proteins

    • Predicted binding affinity to multiple MHC alleles

• Experimental epitope mapping techniques:

• Epitope validation strategy:

  • Generate synthetic peptides corresponding to predicted epitopes

  • Test reactivity with sera from:

    • Naturally infected animals/humans

    • Vaccinated animals

    • Animals protected from challenge after immunization

  • Assess epitope conservation across Brucella species and biovars

  • Evaluate cross-reactivity with related bacterial species

• Immunogenicity assessment:

  • Conjugate identified epitopes to carrier proteins

  • Immunize mice with individual and combined epitopes

  • Evaluate:

    • Antibody titers (IgG, IgG1, IgG2a)

    • T-cell responses (proliferation, cytokine profiles)

    • Protection against challenge

• Epitope optimization:

  • Enhance epitope presentation through:

    • Tandem repeats of B-cell epitopes

    • Incorporation of universal T-helper epitopes

    • Strategic linker design between epitopes

    • Molecular adjuvants (e.g., flagellin, CpG)

This systematic approach has successfully identified protective epitopes in other Brucella outer membrane proteins. For BRA0408/BS1330_II0405, focus on regions that induce both humoral and cell-mediated immunity, as both are critical for protection against intracellular pathogens like Brucella. Combining multiple epitopes from different Brucella immunogens, including BRA0408/BS1330_II0405, may be necessary to achieve robust protection across diverse host species and against different Brucella biovars .