Purification and Characterization of a Black Walnut (Juglans nigra) Allergen, Jug n 4

Identification and semi-quantification of protein allergens in complex mixtures using proteomic and AllerCatPro 2.0 bioinformatic analyses: a proof-of-concept investigation

The demand for botanicals and natural substances in consumer products has increased in recent years. These substances usually contain proteins and these, in turn, can pose a risk for immunoglobulin E (IgE)-mediated sensitization and allergy. However, no method has yet been accepted or validated for assessment of potential allergenic hazards in such materials. In the studies here, a dual proteomic-bioinformatic approach is proposed to evaluate holistically allergenic hazards in complex mixtures of plants, insects, or animal proteins. Twelve commercial preparations of source materials (plant products, dust mite extract, and preparations of animal dander) known to contain allergenic proteins were analyzed by label-free proteomic analyses to identify and semi-quantify proteins. These were then evaluated by bioinformatics using AllerCatPro 2.0 (https://allercatpro.bii.a-star.edu.sg/) to predict no, weak, or strong evidence for allergenicity and similarity to source-specific allergens. In total, 4,586 protein sequences were identified in the 12 source materials combined. Of these, 1,665 sequences were predicted with weak or strong evidence for allergenic potential. This first-tier approach provided top-level information about the occurrence and abundance of proteins and potential allergens. With regards to source-specific allergens, 129 allergens were identified. The sum of the relative abundance of these allergens ranged from 0.8% (lamb's quarters) to 63% (olive pollen). It is proposed here that this dual proteomic-bioinformatic approach has the potential to provide detailed information on the presence and relative abundance of allergens, and can play an important role in identifying potential allergenic hazards in complex protein mixtures for the purposes of safety assessments.

Food Allergens of Plant Origin

This review presents an update on the physical, chemical, and biological properties of food allergens in plant sources, focusing on the few protein families that contribute to multiple food allergens from different species and protein families recently found to contain food allergens. The structures and structural components of the food allergens in the allergen families may provide further directions for discovering new food allergens. Answers as to what makes some food proteins allergens are still elusive. Factors to be considered in mitigating food allergens include the abundance of the protein in a food, the property of short stretches of the sequence of the protein that may constitute linear IgE binding epitopes, the structural properties of the protein, its stability to heat and digestion, the food matrix the protein is in, and the antimicrobial activity to the microbial flora of the human gastrointestinal tract. Additionally, recent data suggest that widely used techniques for mapping linear IgE binding epitopes need to be improved by incorporating positive controls, and methodologies for mapping conformational IgE binding epitopes need to be developed.

From Allergen Molecules to Molecular Immunotherapy of Nut Allergy: A Hard Nut to Crack

Peanuts and tree nuts are two of the most common elicitors of immunoglobulin E (IgE)-mediated food allergy. Nut allergy is frequently associated with systemic reactions and can lead to potentially life-threatening respiratory and circulatory symptoms. Furthermore, nut allergy usually persists throughout life. Whether sensitized patients exhibit severe and life-threatening reactions (e.g., anaphylaxis), mild and/or local reactions (e.g., pollen-food allergy syndrome) or no relevant symptoms depends much on IgE recognition of digestion-resistant class I food allergens, IgE cross-reactivity of class II food allergens with respiratory allergens and clinically not relevant plant-derived carbohydrate epitopes, respectively. Accordingly, molecular allergy diagnosis based on the measurement of allergen-specific IgE levels to allergen molecules provides important information in addition to provocation testing in the diagnosis of food allergy. Molecular allergy diagnosis helps identifying the genuinely sensitizing nuts, it determines IgE sensitization to class I and II food allergen molecules and hence provides a basis for personalized forms of treatment such as precise prescription of diet and allergen-specific immunotherapy (AIT). Currently available forms of nut-specific AIT are based only on allergen extracts, have been mainly developed for peanut but not for other nuts and, unlike AIT for respiratory allergies which utilize often subcutaneous administration, are given preferentially by the oral route. Here we review prevalence of allergy to peanut and tree nuts in different populations of the world, summarize knowledge regarding the involved nut allergen molecules and current AIT approaches for nut allergy. We argue that nut-specific AIT may benefit from molecular subcutaneous AIT (SCIT) approaches but identify also possible hurdles for such an approach and explain why molecular SCIT may be a hard nut to crack.

Physicochemical and functional properties of a protein isolate from maca (Lepidium meyenii) and the secondary structure and immunomodulatory activity of its major protein component

Maca protein isolate (MPI) was extracted from maca root, and its physicochemical and functional properties, and the secondary structure and immunomodulatory activity of its major protein component, MMP, were investigated. The MPI lacked essential amino acids compared with soybean protein isolate (SPI) and casein, but was rich in cysteine and proline. The MPI had rich free sulfhydryl (20.6 μmol g-1), and its surface hydrophobicity (H0, 812.4), oil absorption capacity (7.4 g g-1), foaming capacity (100%) and emulsifying activity (58.2 m2 g-1) were higher than that of SPI. However, the thermal stability (Td, 87.4 °C), foaming stability (75%) and emulsifying stability (26.3 min) of the MPI were weaker than that of the SPI. MMP was a pentamer with a molecular weight of 22 kDa and rich in β-sheets. MMP could significantly enhance the phagocytic capacity and promote the NO, TNF-α and IL-6 secretion of RAW 264.7 cells, involving toll-like receptor 4 and complement receptor 3 mainly.

A graphene oxide-based paper chip integrated with the hybridization chain reaction for peanut and soybean allergen gene detection

Allergen genes of the peanut and soybean were selected as model targets. Four hairpin DNA probes, H1, H2, H3, H4 were designed. Cy3-labeled H1 and H2 were used to detect peanut DNA, while FAM-labeled H3 and H4 were used to detect soybean DNA. Graphene oxide (GO) was used as the adsorption material for capturing the hairpin probes, and as a selective fluorescence quencher to reduce the background signal. To develop an allergen gene detection system with a GO-based paper chip format, we integrated the hybridization chain reaction (HCR) with fluorescence resonance energy transfer (FRET) in our design. The results showed that in the absence of peanut DNA (TP) and soybean DNA (TS), the detection probes attached to the GO surface, which quenched their fluorescence. In the presence of TP or TS, however, complementary probe binding to the targets initiated HCR, producing long double-stranded DNA products that could not be absorbed onto the GO surface. Hence, a strong red or green fluorescent signal was generated. The detection limit for both peanut and soybean DNA was 1 nM using this method, indicating the high sensitivity of our approach. This method also exhibited good specificity and a single chip could be used to simultaneously detect two different targets.

Colorimetric LAMP microfluidic chip for detecting three allergens: peanut, sesame and soybean

Food allergies can greatly harm people's health, and therefore detecting allergens in foods is extremely important. By integrating loop-mediated isothermal amplification (LAMP) with a microfluidic chip, we have developed a method for detecting the allergen genes of peanut (Arachis hypogaea), sesame (Sesamum indicum), and soybean (Glycine max) using a colorimetric method suitable for the naked eye, known as the colorimetric LAMP microfluidic chip. In the presence of peanut, sesame, or soybean in the samples, the corresponding reaction well of the microfluidic chip will appear pink, or otherwise remain light brown. This method of detection is specific and can easily distinguish these three allergens from others in foods. The detection limit for peanut, sesame and soybean allergens was 0.4 ng/μL using the LAMP-microfluidic chip. The accuracy of this novel and rapid method was validated using allergenic foods obtained commercially and was comparable with that of the typical TaqMan real-time PCR method.

Canis familiaris allergen Can f 6: expression, purification and analysis of B-cell epitopes in Chinese dog allergic children

Dog allergy is common worldwide. However, the allergenicity of dog allergy is still unclear in China as well as in special group, such as children. In this study, we chose Can f 6, a major dog allergen which belongs to the lipocalin to study its allergenicity in Chinese dog allergic children. Can f 6 gene was subcloned into pET-28a vector and transformed into E. coli BL21 (DE3) cells for expression. The recombinant Can f 6 was purified by nickel affinity chromatography, identified by SDS-PAGE, and tested for its allergenicity by Western blot with sera and basophil activation test. Secondary structures, B cell epitopes and homology modeling of Can f 6 were predicted by using a series of bioinformatical approaches. And the verification of B cell epitopes was detected by ELISA. The recombinant allergen showed an explicit band with the molecular weight of 20 kDa by SDS-PAGE. Sera from 56.3 % (18/32) of dog-allergic children patients reacted with Can f 6. The induction of the expression of CD63 and CCR3 of dog allergic children in passively sensitized basophils was up to approximately 5.0 times higher than healthy subjects. The secondary structure of Can f 6 contains 3 α-helices, 9 β-sheets and random coils. Five B cell epitopes of Can f 6 were predicted and were confirmed successfully by ELISA. The results showed Can f 6 is a major allergen in Chinese children, which provides a basis for further study of Can f 6 in diagnosis and treatment of symptoms in children in China. The structural information of Can f 6 will help to form a foundation for the future design of vaccines and therapies for Can f 6 related allergies.

Crystal Structure of Cocosin, A Potential Food Allergen from Coconut (Cocos nucifera)

Coconut (Cocos nucifera) is an important palm tree. Coconut fruit is widely consumed. The most abundant storage protein in coconut fruit is cocosin (a likely food allergen), which belongs to the 11S globulin family. Cocosin was crystallized near a century ago, but its structure remains unknown. By optimizing crystallization conditions and cryoprotectant solutions, we were able to obtain cocosin crystals that diffracted to 1.85 Å. The cocosin gene was cloned from genomic DNA isolated from dry coconut tissue. The protein sequence deduced from the predicted cocosin coding sequence was used to guide model building and structure refinement. The structure of cocosin was determined for the first time, and it revealed a typical 11S globulin feature of a double layer doughnut-shaped hexamer.