Homology modeling of allergenic cyclophilins: IgE-binding site and structural basis of cross-reactivity

Molecular characterization of a fungal cyclophilin allergen Rhi o 2 and elucidation of antigenic determinants responsible for IgE-cross-reactivity

Cyclophilins are structurally conserved pan-allergens showing extensive cross-reactivity. So far, no precise information on cross-reactive IgE-epitopes of cyclophilins is available. Here, an 18-kDa IgE-reactive cyclophilin (Rhi o 2) was purified from Rhizopus oryzae, an indoor mold causing allergic sensitization. Based on LC-MS/MS-derived sequences of natural Rhi o 2, the full-length cDNA was cloned, and expressed as recombinant (r) allergen. Purified rRhi o 2 displayed IgE-reactivity and basophil degranulation with sera from all cyclophilin-positive patients. The melting curve of properly folded rRhi o 2 showed partial refolding after heat denaturation. The allergen displayed monomeric functional peptidyl-prolyl cis-trans isomerase (PPIase) activity. In IgE-inhibition assays, rRhi o 2 exhibited extensive cross-reactivity with various other cyclophilins reported as allergens from diverse sources including its homologous human autoantigen. By generating a series of deletion mutants, a conserved 69-residue (Asn⁸¹-Asn¹⁴⁹) fragment at C terminus of Rhi o 2 was identified as crucial for IgE-recognition and cross-reactivity. Grafting of the Asn⁸¹-Asn¹⁴⁹ fragment within the primary structure of yeast cyclophilin CPR1 by replacing its homologous sequence resulted in a hybrid molecule with structural folds similar to Rhi o 2. The IgE-reactivity and allergenic activity of the hybrid cyclophilin were greater than that of CPR1. Therefore, the Asn⁸¹-Asn¹⁴⁹ fragment can be considered as the site of IgE recognition of Rhi o 2. Hence, Rhi o 2 serves as a candidate antigen for the molecular diagnosis of mold allergy, and determination of a major cross-reactive IgE-epitope has clinical potential for the design of next-generation immunotherapeutics against cyclophilin-induced allergies.

Ole e 15 and its human counterpart -PPIA- chimeras reveal an heterogeneous IgE response in olive pollen allergic patients

Olive pollen is a major cause of immunoglobulin E (IgE)-mediated allergy in Mediterranean countries. It is expected to become a worldwide leading allergenic source because olive cultivation is increasing in many countries. Ole e 15 belongs to the cyclophilin pan-allergen family, which includes highly cross-reactive allergens from non-related plant, animal and mold species. Here, the amino acid differences between Ole e 15 and its weak cross-reactive human homolog PPIA were grafted onto Ole e 15 to assess the contribution of specific surface areas to the IgE-binding. Eight Ole e 15-PPIA chimeras were produced in E. coli, purified and tested with 20 sera from Ole e 15-sensitized patients with olive pollen allergy by ELISA experiments. The contribution of linear epitopes was analyzed using twelve overlapping peptides spanning the entire Ole e 15 sequence. All the patients displayed a diverse reduction of the IgE-reactivity to the chimeras, revealing a highly polyclonal and patient-specific response to Ole e 15. IgE-epitopes are distributed across the entire Ole e 15 surface. Two main surface areas containing relevant conformational epitopes have been characterized. This is the first study to identify important IgE-binding regions on the surface of an allergenic cyclophilin.

Spectrum of Allergens and Allergen Biology in India

The growing prevalence of allergy and asthma in India has become a major health concern with symptoms ranging from mild rhinitis to severe asthma and even life-threatening anaphylaxis. The "allergen repertoire" of this subcontinent is highly diverse due to the varied climate, flora, and food habits. The proper identification, purification, and molecular characterization of allergy-eliciting molecules are essential in order to facilitate an accurate diagnosis and to design immunotherapeutic vaccines. Although several reports on prevalent allergens are available, most of these studies were based on preliminary detection and identification of the allergens. Only a few of these allergen molecules have been characterized by recombinant technology and structural biology. The present review first describes the composition, distribution pattern, and natural sources of the predominant allergens in India along with the prevalence of sensitization to these allergens across the country. We go on to present a comprehensive report on the biochemical, immunological, and molecular information on the allergens reported so far from India. The review also covers the studies on allergy- related biosafety assessment of transgenic plants. Finally, we discuss the allergen-specific immunotherapy trials performed in India.

Allergens involved in the cross-reactivity of Aedes aegypti with other arthropods

BACKGROUND

Cross-reactivity between Aedes aegypti and mites, cockroaches, and shrimp has been previously suggested, but the involved molecular components have not been fully described.

OBJECTIVE

To evaluate the cross-reactivity between A aegypti and other arthropods.

METHODS

Thirty-four serum samples from patients with asthma and/or allergic rhinitis were selected, and specific IgE to A aegypti, Dermatophagoides pteronyssinus, Dermatophagoides farinae, Blomia tropicalis, Periplaneta americana. and Litopenaeus vannamei was measured by enzyme-linked immunosorbent assay. Cross-reactivity was investigated using pooled serum samples from allergic patients, allergenic extracts, and the recombinant tropomyosins (Aed a 10.0201, Der p 10, Blo t 10, Lit v 1, and Per a 7). Four IgE reactive bands were further characterized by matrix-assisted laser desorption/ionization tandem time of flight.

RESULTS

Frequency of positive IgE reactivity was 82.35% to at least one mite species, 64.7% to A aegypti, 29.4% to P americana, and 23.5% to L vannamei. The highest IgE cross-reactivity was seen between A aegypti and D pteronyssinus (96.6%) followed by L vannamei (95.4%), B tropicalis (84.4%), and P americana (75.4%). Recombinant tropomyosins from mites, cockroach, or shrimp inhibited the IgE reactivity to the mosquito at a lower extent than the extracts from these arthropods. Several bands of A aegypti cross-reacted with arthropod extracts, and 4 of them were identified as odorant binding protein, mitochondrial cytochrome C, peptidyl-prolyl cis-trans isomerase, and protein with hypothetical magnesium ion binding function.

CONCLUSION

We identified 4 novel cross-reactive allergens in A aegypti allergenic extract. These molecules could influence the manifestation of allergy to environmental allergens in the tropics.

Primary identification, biochemical characterization, and immunologic properties of the allergenic pollen cyclophilin cat R 1

Cyclophilin (Cyp) allergens are considered pan-allergens due to frequently reported cross-reactivity. In addition to well studied fungal Cyps, a number of plant Cyps were identified as allergens (e.g. Bet v 7 from birch pollen, Cat r 1 from periwinkle pollen). However, there are conflicting data regarding their antigenic/allergenic cross-reactivity, with no plant Cyp allergen structures available for comparison. Because amino acid residues are fairly conserved between plant and fungal Cyps, it is particularly interesting to check whether they can cross-react. Cat r 1 was identified by immunoblotting using allergic patients' sera followed by N-terminal sequencing. Cat r 1 (∼ 91% sequence identity to Bet v 7) was cloned from a cDNA library and expressed in Escherichia coli. Recombinant Cat r 1 was utilized to confirm peptidyl-prolyl cis-trans-isomerase (PPIase) activity by a PPIase assay and the allergenic property by an IgE-specific immunoblotting and rat basophil leukemia cell (RBL-SX38) mediator release assay. Inhibition-ELISA showed cross-reactive binding of serum IgE from Cat r 1-allergic individuals to fungal allergenic Cyps Asp f 11 and Mala s 6. The molecular structure of Cat r 1 was determined by NMR spectroscopy. The antigenic surface was examined in relation to its plant, animal, and fungal homologues. The structure revealed a typical cyclophilin fold consisting of a compact β-barrel made up of seven anti-parallel β-strands along with two surrounding α-helices. This is the first structure of an allergenic plant Cyp revealing high conservation of the antigenic surface particularly near the PPIase active site, which supports the pronounced cross-reactivity among Cyps from various sources.

NMR solution structure of Ole e 6, a major allergen from olive tree pollen

Ole e 6 is a pollen protein from the olive tree (Olea europaea) that exhibits allergenic activity with a high prevalence among olive-allergic individuals. The three-dimensional structure of Ole e 6 has been determined in solution by NMR methods. This is the first experimentally determined structure of an olive tree pollen allergen. The structure of this 50-residue protein is based on 486 upper limit distance constraints derived from nuclear Overhauser effects and 24 torsion angle restraints. The global fold of Ole e 6 consists of two nearly antiparallel alpha-helices, spanning residues 3-19 and 23-33, that are connected by a short loop and followed by a long, unstructured C-terminal tail. Viewed edge-on, the structured N terminus has a dumbbell-like shape with the two helices on the outside and with the hydrophobic core, mainly composed of 3 aromatic and 6 cysteine residues, on the inside. All the aromatic rings lie on top of and pack against the three disulfide bonds. The lack of thermal unfolding, even at 85 degrees C, indicates a high conformational stability. Based on the analysis of the molecular surface, we propose five plausible epitopes for IgE recognition. The results presented here provide the structural foundation for future experiments to verify the antigenicity of the proposed epitopes, as well as to design novel hypoallergenic forms of the protein suitable for diagnosis and treatment of type-I allergies. In addition, three-dimensional structure features of Ole e 6 are discussed to provide a basis for future functional studies.