Recombinant Arachis hypogaea Allergen Ara h 1, clone P41B

What is the molecular structure of Ara h 1?

Ara h 1 is a seed storage protein from Arachis hypogaea (peanut) with a bicupin fold in its core region (residues 170-586). The crystal structure reveals that the core region forms trimeric assemblies in its crystalline state, while in solution, it exists as higher molecular weight assemblies. The recombinant Ara h 1 (clone P41B) is a glycosylated polypeptide chain with a calculated molecular mass of 63,484 Dalton and is typically expressed with a 9xHis tag at the N-terminus .

Natural Ara h 1 forms higher molecular weight aggregates in solution, which may result from interactions with small molecular compounds. The formation of these higher-order oligomers is significant as it may influence the allergenicity of the protein .

How do natural and recombinant Ara h 1 differ?

The natural and recombinant forms of Ara h 1 exhibit several key differences:

These differences are significant for researchers, as the choice between natural and recombinant forms can impact experimental outcomes, particularly in immunological studies or structural analyses .

What are the established methods for purifying recombinant Ara h 1?

Recombinant Ara h 1 purification typically involves proprietary chromatographic techniques. The full-length recombinant protein is often produced using a pET9a vector expression system. For the recombinant short Ara h 1 (rsAra h 1, amino acids 170-586), the process involves PCR amplification using the full-length construct as a template, followed by expression in the pET9a vector .

The purified recombinant Ara h 1.0101 protein is typically supplied in 20mM HEPES buffer (pH 8.0) containing 100mM NaCl and 6M Urea. For optimal stability, the protein should be stored at 4°C if used within 2-4 weeks, or at -20°C for longer periods, with care taken to avoid multiple freeze-thaw cycles .

How does temperature affect the structural stability of Ara h 1, and what implications does this have for allergenicity?

Near-infrared spectral analysis of Ara h 1 at different temperatures reveals significant structural changes that may impact its allergenic properties. Principal Component Analysis (PCA) of spectral data shows:

• A mutation point occurs between 55-60°C, indicating substantial structural changes in the protein

• At temperatures approaching 80°C, flocculent precipitation is observed, suggesting protein denaturation

• During heating, a blue shift occurs in the peak around 1,450 nm (moving from 1,454 to 1,425 nm)

• An isothermal point forms near 1,441 nm

These spectral changes reflect alterations in the water solvation shell surrounding the protein, which directly affects the Ara h 1 structure. The significant structural transition at 55-60°C may modify epitope exposure or conformation, potentially altering the protein's ability to bind IgE antibodies .

This temperature sensitivity has important implications for food processing methods and their impact on allergenicity. Researchers should consider these thermal transition points when designing thermal processing studies or when preparing recombinant Ara h 1 for immunological assays.

What T-cell epitopes have been identified in Ara h 1, and how can they be studied?

Multiple T-cell epitopes have been identified in Ara h 1 using Tetramer Guided Epitope Mapping (TGEM). A total of 20 epitopes have been identified, restricted by multiple HLA class II alleles including DR0101, DR0301, DR0401, DR0404, DR1101, DR1401, DR1502, and DRB5 .

Some of the specific epitopes identified include:

• Ara h 1 169-188 (DR1101-restricted)

• Ara h 1 321-340 (DR1101-restricted)

• Ara h 1 457-476 (DR1101-restricted)

• Ara h 1 465-484 (DR1101-restricted)

The methodology for identifying and studying these epitopes involves:

• Synthesizing overlapping peptides spanning the entire Ara h 1 sequence (77 peptides, 20 amino acids in length with 12 amino acid overlap)

• Dividing these peptides into pools

• Loading peptide mixtures into biotinylated HLA-DR proteins to generate pooled tetramers

• Culturing cells for 14 days before staining with pooled peptide tetramers

• Re-staining positive wells with tetramers loaded with individual peptides from the positive pool

• Using anti-PE magnetic beads to enrich for PE-labeled tetramer-positive cells for ex vivo characterization

This approach enables researchers to characterize the frequency, phenotype, and cytokine profiles of Ara h 1-specific T cells in peanut-allergic and non-allergic individuals.

How do Ara h 1-specific T cells from allergic individuals differ from those of non-allergic individuals?

Research has revealed significant differences in Ara h 1-specific T cells between peanut-allergic and non-allergic individuals:

• Frequency: Peanut-allergic subjects show approximately 9 Ara h 1-reactive T cells per million peripheral blood cells, while non-atopic subjects and atopic subjects without peanut allergy show less than 1 cell per million

• Phenotypic characteristics:

  • Ara h 1-specific CD4+ T cells in allergic subjects express CCR4 (a Th2-associated chemokine receptor)

  • These cells do not express CRTH2 (another Th2 marker)

  • A relatively low percentage express β7 integrin compared to total CD4+ T cells

• Cytokine profile: Ara h 1-reactive T cells from allergic individuals produce a mixed cytokine profile, including:

  • Th2 cytokines: IL-4, IL-5

  • Th1 cytokine: IFN-γ

  • Regulatory cytokine: IL-10

  • Th17 cytokine: IL-17

These findings have important implications for understanding the immunological basis of peanut allergy and developing targeted immunotherapies.

What are the challenges in crystallizing natural Ara h 1, and how has this been addressed with recombinant variants?

Despite testing approximately 1,500 different conditions, researchers have been unable to obtain crystals of natural Ara h 1. This crystallization challenge likely stems from the protein's tendency to form higher molecular weight aggregates in solution, resulting in heterogeneity that impedes crystal formation .

To overcome this obstacle, researchers have successfully employed a truncated recombinant version of Ara h 1 (rsAra h 1, residues 170-586) for crystallization studies. This core fragment was selected because it had previously demonstrated stability and crystallization potential .

The successful crystallization of the recombinant core fragment has revealed that:

• The central part of Ara h 1 has a bicupin fold

• In its crystalline state, the core forms trimeric assemblies

• The residues in this core region are sufficient for the formation of Ara h 1 trimers and higher-order oligomers

This approach demonstrates how protein engineering can be used to overcome crystallization challenges with allergens, providing valuable structural information even when the natural protein proves recalcitrant to crystallization.

What are the optimal conditions for expressing and purifying functional recombinant Ara h 1?

Based on published research, optimal conditions for expression and purification of functional recombinant Ara h 1 include:

Expression Systems:

• The full-length recombinant Ara h 1 has been successfully produced using a pET9a vector system

• Recombinant Ara h 1.0101 has been expressed in Sf9 insect cells, which allows for glycosylation similar to the natural protein

Purification Strategy:

• Initial capture using affinity chromatography (leveraging the 9xHis tag at the N-terminus)

• Further purification via proprietary chromatographic techniques to achieve >95% purity as determined by SDS-PAGE

• Formulation in 20mM HEPES buffer (pH 8.0) with 100mM NaCl and 6M Urea

Quality Control Metrics:

• SDS-PAGE analysis to confirm >95% purity

• Immunological testing to verify IgE binding capacity

• Immunodot test with positive/negative sera panels to confirm allergenicity

• Structural verification through techniques such as circular dichroism or small-angle X-ray scattering

Researchers should note that the recombinant protein may exhibit different structural and immunological properties compared to the natural allergen, which should be considered when designing experiments.

How can in vitro digestion assays be used to compare stability between natural and recombinant Ara h 1?

In vitro gastric and duodenal digestion assays provide valuable insights into the stability of different Ara h 1 variants and their potential allergenicity. Research has shown that the natural protein is the most stable form, followed by the recombinant Ara h 1 core fragment, with the full-length recombinant protein being the least stable .

Methodology for in vitro digestion assays:

• Sample preparation:

  • Purify natural Ara h 1, full-length recombinant Ara h 1, and recombinant core Ara h 1

  • Standardize protein concentrations

• Gastric phase digestion:

  • Adjust samples to gastric pH (typically 2.0-3.0)

  • Add pepsin at physiologically relevant enzyme:protein ratios

  • Incubate at 37°C with gentle agitation

  • Collect aliquots at various time points (0, 1, 2, 5, 10, 20, 60 minutes)

• Duodenal phase digestion:

  • Adjust pH to duodenal conditions (≈6.5-7.5)

  • Add pancreatin and bile salts at physiological concentrations

  • Continue incubation at 37°C

  • Collect samples at relevant time points

• Analysis methods:

  • SDS-PAGE to visualize protein degradation patterns

  • Western blotting with patient sera to assess IgE binding to digestion fragments

  • Mass spectrometry to identify persistent peptide fragments

• Data interpretation:

  • Compare degradation rates between protein variants

  • Identify stable fragments that may contribute to allergenicity

  • Correlate findings with known epitope regions

This experimental approach provides insights into how different forms of Ara h 1 might be processed during digestion, which has implications for understanding allergenicity and designing hypoallergenic variants.

What techniques are most effective for studying temperature-induced structural changes in Ara h 1?

Based on the search results, several techniques have proven effective for studying temperature-induced structural changes in Ara h 1:

Near-Infrared Spectroscopy with Temperature Control:

• Matrix-F near-infrared spectrometer equipped with a temperature controlling device (qpod2e)

• Temperature range: 25°C to 80°C

• Spectral range: 1,250-1,667 nm (focusing on water O-H overtone band)

• This approach allows for non-destructive analysis of protein conformational changes through water-protein interactions

Multivariate Data Analysis Techniques:

Aquaphotomics Approach:

• Using water as a probe to indirectly investigate protein structural changes

• Analyzing shifts in water absorption bands as indicators of changes in the water solvation shell around the protein

• This method is particularly useful when direct protein signals are weak due to high water content

Complementary Techniques:

• Circular Dichroism (CD) spectroscopy to monitor secondary structure changes

• Differential Scanning Calorimetry (DSC) to measure thermal transition points

• Dynamic Light Scattering (DLS) to track aggregation behavior at different temperatures

When designing experiments to study temperature effects on Ara h 1, researchers should be aware of the critical transition range (55-60°C) and precipitation observed at higher temperatures, which may affect experimental outcomes and interpretation.

How do the IgE binding patterns differ between natural and recombinant Ara h 1, and what are the implications for diagnostic applications?

Research has shown that natural Ara h 1 and its recombinant variants demonstrate different patterns of interaction with IgE antibodies from peanut-allergic patients. These differences have important implications for diagnostic test development and allergen standardization .

Key findings on IgE binding patterns:

• Natural Ara h 1 (nAra h 1) and recombinant variants can be distinguished by their IgE binding profiles when tested with sera from peanut-allergic individuals

• The differences in binding patterns likely result from:

  • Structural variations (aggregation states, folding)

  • Post-translational modifications present in natural but not recombinant proteins

  • Differences in stability and epitope accessibility

Methodological approaches to study IgE binding:

• Western blots following SDS-PAGE separation of proteins (300 ng/protein)

• Spot blots on PVDF membranes

• Testing with 1:10 dilutions of sera from individuals with confirmed peanut allergy (positive ImmunoCAP and skin prick test results)

• Comparison of binding patterns across multiple patient samples

Implications for diagnostics and research:

• Diagnostic tests using recombinant Ara h 1 may not fully replicate the sensitivity of tests using natural allergens

• When developing component-resolved diagnostics, researchers should consider which form of Ara h 1 provides optimal clinical sensitivity and specificity

• For mechanistic studies of allergic responses, researchers should be aware that experimental findings might differ depending on whether natural or recombinant allergen is used

• Standardization efforts for allergenic products should account for these structural and immunological differences

What is the current understanding of cross-reactivity between Ara h 1 and homologous proteins from other plant species?

The molecular basis of cross-reactivity between Ara h 1 and other vicilin allergens has been elucidated through structural and immunological studies. This information is valuable for understanding allergic cross-reactions and improving diagnostic approaches .

Key findings on cross-reactivity:

• Structural homology: Ara h 1 shares structural similarities with other vicilin proteins from diverse plant species. Bioinformatics and clustering analysis have identified groups of similar sequences, revealing the evolutionary relationships between Ara h 1 and its homologs .

• Common epitopes: Shared epitope regions have been identified between Ara h 1 and vicilins from:

  • Tree nuts (walnut, hazelnut)

  • Legumes (soy, chickpea, lentil)

  • Seeds (sesame, buckwheat)

• Cross-reactive carbohydrate determinants (CCDs): Some cross-reactivity may be attributed to similar glycosylation patterns rather than peptide epitopes

Methodological approaches to study cross-reactivity:

• Sequence alignment and phylogenetic analysis

• Structural modeling and epitope mapping

• IgE inhibition assays to quantify cross-reactivity

• Basophil activation tests to assess functional cross-reactivity

Clinical implications:

• Patients allergic to peanuts may experience reactions to cross-reactive foods, even without prior exposure

• Understanding these relationships helps in designing more precise diagnostic tests that can distinguish true sensitization from cross-reactivity

• Identification of conserved epitopes can inform the development of broad-spectrum immunotherapies

How can T cell epitope mapping of Ara h 1 contribute to the development of immunotherapy approaches?

T cell epitope mapping of Ara h 1 provides critical insights that can guide the development of targeted immunotherapy approaches for peanut allergy. The identification of specific T cell epitopes and understanding their HLA restriction patterns offers several potential applications :

Contributions to immunotherapy development:

• Peptide-based immunotherapy design:

  • Identified epitopes (such as Ara h 1 169-188, 321-340, 457-476) can be used to design peptide vaccines

  • Peptides containing these epitopes could be modified to maintain T cell recognition while reducing IgE binding

• HLA-based personalization:

  • The 20 identified epitopes with defined HLA restriction (DR0101, DR0301, DR0401, DR0404, DR1101, DR1401, DR1502, and DRB5) enable HLA-tailored approaches

  • Patients could be stratified based on their HLA haplotypes to predict which epitopes would be most relevant for their treatment

• Monitoring therapeutic responses:

  • The ability to detect and track Ara h 1-specific T cells using tetramers provides a tool for monitoring immunotherapy

  • Changes in the frequency, phenotype, or cytokine profile of allergen-specific T cells could serve as biomarkers of treatment efficacy

• Tolerogenic approaches:

  • Understanding that Ara h 1-reactive T cells in allergic individuals produce a mix of cytokines (IFN-γ, IL-4, IL-5, IL-10, IL-17) helps in designing approaches to shift the balance toward tolerance

  • Targeting specific pathways to enhance IL-10 production or reduce Th2 cytokines

Methodological considerations:

• Tetramer Guided Epitope Mapping (TGEM) provides a powerful tool for identifying relevant T cell epitopes

• HLA class II tetramers loaded with identified epitopes enable tracking of rare allergen-specific T cells

• Phenotypic analysis of tetramer-positive cells (analyzing markers like CCR4 and β7 integrin) provides insights into homing and functional properties

• Cytokine profiling helps understand the balance between pro-allergic and regulatory responses

The frequency difference of Ara h 1-reactive T cells between allergic (9 cells per million) and non-allergic individuals (<1 cell per million) suggests that quantitative as well as qualitative differences in T cell responses contribute to the allergic phenotype, further informing therapeutic strategies.

What are the key knowledge gaps in understanding Ara h 1 structure-function relationships?

Several important knowledge gaps remain in our understanding of Ara h 1 structure-function relationships that warrant further investigation:

• Relationship between oligomerization and allergenicity:

  • While we know natural Ara h 1 forms higher molecular weight aggregates and recombinant versions show different oligomerization states, the precise impact of these differences on allergenicity is not fully elucidated

  • The role of small molecular compounds in driving aggregation requires further exploration

• Epitope exposure in different conformational states:

  • How temperature-induced structural changes (particularly at the 55-60°C transition point) affect epitope exposure

  • Whether certain aggregation states preferentially expose specific IgE epitopes

• Post-translational modifications:

  • The exact nature and location of glycosylation in natural Ara h 1 and its impact on immunogenicity

  • How other post-translational modifications might influence protein stability and allergenic potential

• Digestion-resistant epitopes:

  • While digestion stability differences have been observed between natural and recombinant Ara h 1, the specific fragments that resist digestion and their epitope content need further characterization

  • The relationship between digestion resistance and clinical reactivity

• Structural basis for cross-reactivity:

  • Detailed mapping of conserved structural features responsible for cross-reactivity with other vicilin allergens

  • Identification of unique structural features that could explain peanut-specific allergenicity

Future structural studies employing advanced techniques like cryo-electron microscopy, hydrogen-deuterium exchange mass spectrometry, and molecular dynamics simulations could help address these knowledge gaps.

How might emerging technologies enhance the study of Ara h 1 and its role in peanut allergy?

Emerging technologies offer promising approaches to advance our understanding of Ara h 1 and peanut allergy through enhanced resolution, throughput, and integrative analysis:

• Single-cell technologies:

  • Single-cell RNA sequencing of Ara h 1-reactive T cells to reveal heterogeneity within allergen-specific populations

  • Single-cell proteomics to characterize the full repertoire of cytokines produced by individual allergen-specific cells

  • These approaches could reveal subpopulations of cells with distinct roles in allergy or tolerance

• Advanced structural biology techniques:

  • Cryo-electron microscopy to visualize Ara h 1 oligomers in their native state without crystallization

  • Neutron scattering to better understand protein-water interactions and conformational changes

  • These methods could overcome the crystallization challenges faced with natural Ara h 1

• Systems biology approaches:

  • Multi-omics integration to connect genetic factors, protein structure, and immune responses

  • Network analysis to identify key regulatory nodes in allergic responses to Ara h 1

  • These integrative approaches could reveal novel therapeutic targets

• Advanced spectroscopic methods:

  • Two-dimensional infrared spectroscopy for enhanced resolution of protein structural changes

  • Raman spectroscopy for label-free analysis of protein structure in complex matrices

  • These techniques could build upon the NIR spectroscopy findings regarding temperature-induced structural changes

• In silico prediction tools:

  • Improved computational models for predicting T and B cell epitopes

  • Molecular dynamics simulations to understand protein flexibility and epitope exposure

  • These computational approaches could accelerate epitope discovery and vaccine design

The integration of these technologies with established methods could provide unprecedented insights into Ara h 1 structure, function, and immunology, ultimately leading to improved diagnostic and therapeutic approaches for peanut allergy.