Allergenicity and structural properties of new Cor a 1 isoallergens from hazel identified in different plant tissues.

The hazel allergen Cor a 1 is a PR-10 protein, closely related to the major birch pollen allergen Bet v 1. Hazel allergies are caused by cross-reactive IgE antibodies originally directed against Bet v 1. Despite the importance of PR-10 proteins in allergy development, their function and localization in the plant remain largely elusive. Therefore, the presence of Cor a 1 mRNA and proteins was investigated in different tissues, i.e., the female flower, immature and mature nuts, catkins, and pollen. Four yet unknown Cor a 1 isoallergens, i.e., Cor a 1.0501-1.0801, and one new Cor a 1.03 variant were discovered and characterized. Depending on the isoallergen, the occurrence and level of mRNA expression varied in different tissues, suggesting different functions. Interestingly, Cor a 1.04 previously thought to be only present in nuts, was also detected in catkins and pollen. The corresponding Cor a 1 genes were expressed in Escherichia coli. The purified proteins were analysed by CD and NMR spectroscopy. Immunoblots and ELISAs to determine their allergenic potential showed that the new proteins reacted positively with sera from patients allergic to birch, hazel and elder pollen and were recognized as novel isoallergens/variants by the WHO/IUIS Allergen Nomenclature Sub-Committee.

Identification of a natural ligand of the hazel allergen Cor a 1.

Hazelnut is one of the most frequent causes of food allergy. The major hazel allergen in Northern Europe is Cor a 1, which is homologous to the major birch pollen allergen Bet v 1. Both allergens belong to the pathogenesis related class PR-10. We determined the solution structure of Cor a 1.0401 from hazelnut and identified a natural ligand of the protein. The structure reveals the protein fold characteristic for PR-10 family members, which consists of a seven-stranded antiparallel ß-sheet, two short α-helices arranged in V-shape and a long C-terminal α-helix encompassing a hydrophobic pocket. However, despite the structural similarities between Cor a 1 and Bet v 1, they bind different ligands. We have shown previously that Bet v 1 binds to quercetin-3-O-sophoroside. Here, we isolated Cor a 1 from hazel pollen and identified the bound ligand, quercetin-3-O-(2"-O-ß-D-glucopyranosyl)-ß-D-galactopyranoside, by mass spectrometry and nuclear magnetic resonance spectroscopy (NMR). NMR experiments were performed to confirm binding. Remarkably, although it has been shown that PR-10 allergens show promiscuous binding behaviour in vitro, we can demonstrate that Cor a 1.0401 and Bet v 1.0101 exhibit highly selective binding for their specific ligand but not for the respective ligand of the other allergen.

Quality and potency profile of eight recombinant isoallergens, largely mimicking total Bet v 1-specific IgE binding of birch pollen.

BACKGROUND: To date, only limited information on structure, expression levels and IgE binding of Bet v 1 variants, which are simultaneously expressed in birch pollen, is available. OBJECTIVE: To analyse and compare structure and serum IgE/IgG binding of rBet v 1 variants to Bet v 1.0101. METHODS: Recombinant Bet v 1 variants were studied with sera of 20 subjects allergic to birch pollen. Folding, aggregation and solubility of the rBet v 1 variants were analysed to attribute diverging IgE binding to either allergen structure or methodological features. IgE/IgG binding was studied with rBet v 1 in solution or adsorbed to solid phases. Allergen-mediated cross-linking of FcεRI receptors was determined by mediator release of sensitized humanized rat basophil leukaemia cells. RESULTS: All variants, except for rBet v 1.0113, were monomeric and had Bet v 1-type conformation. Serum IgE binding to variants adsorbed to solid phase was reduced to 6.6%-36.5% compared with Bet v 1.0101. In contrast, inhibition of IgE binding to Bet v 1.0101 by rBet v 1 variants ranged from 62% to 83%. Similarly, mediator release ranged from 30.7% to 55.2% for all variants and was only clearly reduced for rBet v 1.0301 (10.4%). The IgE-binding potency of rBet v 1 variants representing their native quantities in birch pollen was only slightly lower compared to extract. IgG binding to variants was between 50.9% and 134.5% compared with rBet v 1.0101 (100%). CONCLUSION AND CLINICAL RELEVANCE: Bet v 1 variants previously classified as hypoallergenic can exhibit similar functional IgE binding as Bet v 1.0101. Eight rBet v 1 variants largely reproduce total Bet v 1-specific IgE binding of birch pollen extracts. Assay format-dependent variation in IgE-binding properties needs to be considered in the development of diagnostic or therapeutic products.

Conjugation of wildtype and hypoallergenic mugwort allergen Art v 1 to flagellin induces IL-10-DC and suppresses allergen-specific TH2-responses in vivo.

Allergies to weed pollen including members of the Compositae family, such as mugwort, ragweed, and feverfew are spreading worldwide. To efficiently treat these newly arising allergies, allergen specific immunotherapy needs to be improved. Therefore, we generated novel vaccine candidates consisting of the TLR5-ligand Flagellin A from Listeria and the major mugwort allergen Art v 1 including either the wild type Art v 1 sequence (rFlaA:Artv1) or a hypoallergenic variant (rFlaA:Artv1hyp) with reduced IgE-binding capacity. Immune modulating capacity of these constructs and respective controls was evaluated in vitro and in vivo. Incorporation of hypoallergenic Art v 1 derivative did not interfere with the resulting fusion proteins' immune stimulatory capacity. Both rFlaA:Artv1 and rFlaA:Artv1hyp induced a prominent, mTOR-dependent, IL-10 secretion from murine dendritic cells, and suppressed allergen-specific TH2-cytokine secretion in vitro and in vivo. Both conjugates retained the capacity to induce rFlaA-specific antibody responses while efficiently inducing production of Art v 1-specific IgG1 and IgG2a antibodies in mice. Interestingly, only the suppression of TH2-cytokine secretion by rFlaA:Artv1 (but not rFlaA:Artv1hyp) was paralleled by a strong secretion of IFN-γ. In summary, we provided evidence that incorporating hypoallergens into flagellin:allergen fusion proteins is a suitable strategy to further improve these promising vaccine candidates.

Model for Quality Control of Allergen Products with Mass Spectrometry.

Birch pollen allergy is diagnosed and treated with aqueous extracts from birch pollen, which contain a mixture of allergens and nonallergenic proteins, including large numbers of closely related sequence variants, so-called iso-allergens of the major allergen, Bet v 1. The quality of therapeutic and diagnostic allergen products largely depends on the allergen and iso-allergen composition. Several biochemical methods are currently applied to detect and quantify allergens and to record protein profiles without differentiating between iso-allergens. Mass spectrometry (MS) may entirely replace these technologies, as it allows sequence specific identification and quantification of proteins and protein profiles including sequence variants in one run. However, the protein inference problem still hampers the automatic assignment of peptide sequences to proteins, consequently impeding the quantification of sequence variants. Therefore, the aim of the study was to set up semitargeted analyses of label-free MS data that allow unambiguous identification and quantification of birch pollen allergens and nonallergenic proteins. We combined data independent acquisition with manual assignment of predefined target sequences for quantification of iso-allergens and automatic quantification of other allergens and nonallergenic proteins. The quantitative data for birch pollen allergens and sequence variants of Bet v 1 were further confirmed by multiple reaction monitoring.

Quality Control of Biomedicinal Allergen Products - Highly Complex Isoallergen Composition Challenges Standard MS Database Search and Requires Manual Data Analyses.

Allergy against birch pollen is among the most common causes of spring pollinosis in Europe and is diagnosed and treated using extracts from natural sources. Quality control is crucial for safe and effective diagnosis and treatment. However, current methods are very difficult to standardize and do not address individual allergen or isoallergen composition. MS provides information regarding selected proteins or the entire proteome and could overcome the aforementioned limitations. We studied the proteome of birch pollen, focusing on allergens and isoallergens, to clarify which of the 93 published sequence variants of the major allergen, Bet v 1, are expressed as proteins within one source material in parallel. The unexpectedly complex Bet v 1 isoallergen composition required manual data interpretation and a specific design of databases, as current database search engines fail to unambiguously assign spectra to highly homologous, partially identical proteins. We identified 47 non-allergenic proteins and all 5 known birch pollen allergens, and unambiguously proved the existence of 18 Bet v 1 isoallergens and variants by manual data analysis. This highly complex isoallergen composition raises questions whether isoallergens can be ignored or must be included for the quality control of allergen products, and which data analysis strategies are to be applied.

Novel isoforms of Pru av 1 with diverging immunoglobulin E binding properties identified by a synergistic combination of molecular biology and proteomics.

Birch pollen-related food allergies are mainly associated to Bet v 1. Little is known about isoforms of Bet v 1 homologous in fruit of the Rosaceae family. We attempted to identify novel isoforms of Pru av 1, the major cherry allergen, at the cDNA and the protein level by a combination of molecular biology and proteomic tools. A cDNA library was screened with patients immunoglobulin E (IgE) and a specific hybridization probe. Edman sequencing, mass spectrometry (MS), and MS/MS were performed after detecting Pru av 1 on 2-D maps by immunoblotting using patients IgE and a monoclonal antibody. Partial amino acid sequences were completed with a polymerase chain reaction (PCR) strategy. The IgE-binding properties of the Pru av 1 spots were analyzed by 2-D blot inhibition. cDNA library analysis revealed a novel Pru av 1 isoform. MS and N-terminal sequencing confirmed the cDNA sequences at the protein level. A series of spots were confirmed as the already known Pru av 1. One spot, exclusively detected with patients sera, was identified as the novel isoform. A partial amino acid sequence detected with MS/MS was completed by PCR-cloning. The 2-D blot inhibition revealed epitope differences between the novel isoform and the previously published Pru av 1. Our data demonstrate that a synergistic combination of molecular biology and proteomics represents a powerful tool for reliable and comprehensive identification of allergen isoforms and variants. The newly identified isoform showed diverging IgE-binding properties and may be relevant for the diagnosis or therapy of cherry allergy.