Food Allergen Epitope Mapping

Investigation into potential allergenicity of DBD plasma-treated casein digestion products based on immunoglobulin E linear epitopes and the sensitized-cell model

The study aimed to investigate the allergenicity change in casein treated with dielectric barrier discharge (DBD) plasma during in vitro simulated digestion, focusing on the immunoglobulin E (IgE) linear epitopes and utilizing a sensitized-cell model. Results indicated that prior treatment with DBD plasma treatment (4 min) before simulated digestion led to a 10.5% reduction in the IgE-binding capacity of casein digestion products. Moreover, the release of biologically active substances induced from KU812 cells, including β-HEX release rate, human histamine, IL-4, IL-6, and TNF-α, decreased by 2.1, 28.1, 20.6, 11.6, and 17.3%, respectively. Through a combined analysis of LC-MS/MS and immunoinformatics tools, it was revealed that DBD plasma treatment promoted the degradation of the IgE linear epitopes of casein during digestion, particularly those located in the α-helix region of αs1-CN and αs2-CN. These findings suggest that DBD plasma treatment prior to digestion may alleviate casein allergic reactions.

Animal-derived food allergen: A review on the available crystal structure and new insights into structural epitope

Immunoglobulin E (IgE)-mediated food allergy is a rapidly growing public health problem. The interaction between allergens and IgE is at the core of the allergic response. One of the best ways to understand this interaction is through structural characterization. This review focuses on animal-derived food allergens, overviews allergen structures determined by X-ray crystallography, presents an update on IgE conformational epitopes, and explores the structural features of these epitopes. The structural determinants of allergenicity and cross-reactivity are also discussed. Animal-derived food allergens are classified into limited protein families according to structural features, with the calcium-binding protein and actin-binding protein families dominating. Progress in epitope characterization has provided useful information on the structural properties of the IgE recognition region. The data reveals that epitopes are located in relatively protruding areas with negative surface electrostatic potential. Ligand binding and disulfide bonds are two intrinsic characteristics that influence protein structure and impact allergenicity. Shared structures, local motifs, and shared epitopes are factors that lead to cross-reactivity. The structural properties of epitope regions and structural determinants of allergenicity and cross-reactivity may provide directions for the prevention, diagnosis, and treatment of food allergies. Experimentally determined structure, especially that of antigen-antibody complexes, remains limited, and the identification of epitopes continues to be a bottleneck in the study of animal-derived food allergens. A combination of traditional immunological techniques and emerging bioinformatics technology will revolutionize how protein interactions are characterized.

Localization of G1A1a Allergenic Domain Destroyed by Thermal Processing

Glycinin is an important allergenic protein. A1a is the acidic chain of the G1 subunit in glycinin (G1A1a), and it has strong allergenicity. In this study, we used phage display technology to express the protein of G1A1a and its overlapping fragments and an indirect enzyme-linked immunosorbent assay (iELISA) to determine the antigenicity and allergenicity of the expressed protein. After three rounds of screening, it was determined that fragment A1a-2-B-I (151SLENQLDQMPRRFYLAGNQEQEFLKYQQEQG181) is the allergenic domain of G1A1a destroyed by thermal processing. In addition, three overlapping peptides were synthesized from fragments A1a-2-B-I, and a linear epitope was found in this domain through methods including dot blot and iELISA. Peptide 2 (157DQMPRRFYLANGNQE170) showed allergenicity, and after replacing it with alanine, it was found that amino acids D157, Q158, M159, and Y164 were the key amino acids that affected its antigenicity, while Q158, M159, R162, and N168 affected allergenicity.

Exploration of digestion-resistant immunodominant epitopes in shrimp (Penaeus vannamei) allergens

The digestion products of Penaeus vannamei still had sensitizing and eliciting capacity; however, the underlying mechanism has not been identified. This study analyzed the structural changes of shrimp proteins during digestion, predicted the linearmimotopepeptides and first validated the allergenicity of immunodominantepitopes with binding ability. The results showed that the shrimp proteins were gradually degraded into small peptides during digestion, which might lead to the destruction of linear epitopes. However, these peptides carried IgE epitopes that still trigger allergic reactions. Eighteen digestion-resistant epitopes were predicted by multiple immunoinformatics tools and digestomics. Five epitopes contained more critical amino acids and had strong molecular docking (P1: DSGVGIYAPDAEA, P2: EGELKGTYYPLTGM, P3: GRQGDPHGKFDLPPGV, P4: IFAWPHKDNNGIE, P5: KSTESSVTVPDVPSIHD), and these epitopes were identified as novel IgE binding immunodominantepitopes in Penaeus vannamei. These findings provide novel insight into allergenic epitopes, which might serve as key targets for reducing the allergenicity in shrimp.

Mutation of Disulfide Bond Sites Reduces the Immunoreactivity of Cra a 4 by Changing the Structural Characteristics

Sarcoplasmic calcium-binding protein (Cra a 4) from Crassostrea angulata belongs to the EF-hand superfamily, and understanding of its structure-allergenicity relationship is still insufficient. In this study, chemical denaturants were used to destroy the structure of Cra a 4, showing that disruption of the structure reduced its IgG-/IgE-binding activity. To explore which critical amino acid site affects the allergenicity of Cra a 4, the mutants were obtained by site-directed mutations in the disulfide bonds site (C97), conformational epitopes (I105, D114), or Ca2+-binding region (D106, D110) and their IgG-/IgE-binding activity was reduced significantly using serological tests. Notably, C97A had the lowest immunoreactivity. In addition, two conformational epitopes of Cra 4 were verified. Meanwhile, the increase of the α-helical content, surface hydrophobicity, and surface electrostatic potential of C97A affected its allergenicity. Overall, the understanding of the structure-allergenicity relationship of Cra a 4 allowed the development of a hypoallergenic mutant.

Electrical Fields in the Processing of Protein-Based Foods

Electric field-based technologies offer interesting perspectives which include controlled heat dissipation (via the ohmic heating effect) and the influence of electrical variables (e.g., electroporation). These factors collectively provide an opportunity to modify the functional and technological properties of numerous food proteins, including ones from emergent plant- and microbial-based sources. Currently, numerous scientific studies are underway, contributing to the emerging body of knowledge about the effects on protein properties. In this review, "Electric Field Processing" acknowledges the broader range of technologies that fall under the umbrella of using the direct passage of electrical current in food material, giving particular focus to the ones that are industrially implemented. The structural and biological effects of electric field processing (thermal and non-thermal) on protein fractions from various sources will be addressed. For a more comprehensive contextualization of the significance of these effects, both conventional and alternative protein sources, along with their respective ingredients, will be introduced initially.

Characterization of Linear IgE-Binding Epitopes in Food Allergens

An IgE epitope is a part of an allergen that is capable of binding to IgE antibodies and eliciting an immune response. Identifying and characterizing human-allergy-relevant epitopes are important for diagnosis and prognosis of food allergy and development of immunotherapy treatments. This chapter describes the protocol for manual synthesis of overlapping peptides on a cellulose membrane and subsequent dot blotting of the peptides with allergic patients' IgE to map the linear IgE-binding epitopes in food allergens.

ACE configurator for ELISpot: optimizing combinatorial design of pooled ELISpot assays with an epitope similarity model

The enzyme-linked immunosorbent spot (ELISpot) assay is a powerful in vitro immunoassay that enables cost-effective quantification of antigen-specific T-cell reactivity. It is used widely in the context of cancer and infectious diseases to validate the immunogenicity of predicted epitopes. While technological advances have kept pace with the demand for increased throughput, efforts to increase scale are bottlenecked by current assay design and deconvolution methods, which have remained largely unchanged. Current methods for designing pooled ELISpot experiments offer limited flexibility of assay parameters, lack support for high-throughput scenarios and do not consider peptide identity during pool assignment. We introduce the ACE Configurator for ELISpot (ACE) to address these gaps. ACE generates optimized peptide-pool assignments from highly customizable user inputs and handles the deconvolution of positive peptides using assay readouts. In this study, we present a novel sequence-aware pooling strategy, powered by a fine-tuned ESM-2 model that groups immunologically similar peptides, reducing the number of false positives and subsequent confirmatory assays compared to existing combinatorial approaches. To validate ACE's performance on real-world datasets, we conducted a comprehensive benchmark study, contextualizing design choices with their impact on prediction quality. Our results demonstrate ACE's capacity to further increase precision of identified immunogenic peptides, directly optimizing experimental efficiency. ACE is freely available as an executable with a graphical user interface and command-line interfaces at https://github.com/pirl-unc/ace.

Digestion-Resistant Linear Epitopes as Dominant Contributors to Strong Allergenicity of Tropomyosin in Antarctic Krill (Euphausia superba)

Although tropomyosin has been identified as a major allergen in Antarctic krill, the digestive fate of Antarctic krill tropomyosin and its relationship with allergenicity are unknown. In this study, Antarctic krill tropomyosin was administered to BALB/c mice via both gavage and intraperitoneal injection to explore its sensitizing and eliciting capacity, and its digestion products were analyzed for structural changes and digestion-resistant linear epitopes. Mice gavaged with tropomyosin exhibited lower levels of specific IgE and IgG1, mast cell degranulation, vascular permeability, and anaphylaxis symptoms than those in the intraperitoneal injection group. This may be due to the destruction of macromolecular aggregates, loose expansion of the tertiary structure, complete disappearance of α-helix, and significant changes in molecular force upon the digestion of tropomyosin. Nevertheless, the intragastric administration of Antarctic krill tropomyosin still triggered strong allergic reactions, which was attributed to the existence of seven digestion-resistant linear epitopes (Glu26-His44, Thr111-Arg125, Glu157-Glu164, Glu177-Gly186, Val209-Ile225, Arg244-Arg255, and Val261-Ile270).

Food allergen analysis: A review of current gaps and the potential to fill them by matrix-assisted laser desorption/ionization

Food allergy remains a public health, business, and regulatory challenge. Risk analysis (RA) and risk management (RM) of food allergens are of great importance and analysis for food allergens is necessary for both. The current workhorse techniques for allergen analysis (enzyme linked immunosorbent assay [ELISA] and real-time polymerase chain reaction) exhibit recognized challenges including variable and antibody specific responses and detection of species DNA rather than allergen protein, respectively. Liquid chromatography-tandem mass spectrometry (LC-MS/MS) enables protein identification, with potential for multiplex analysis and traceability to the System of International units (SI), aiding global measurement standardization. In this review, recent literature has been systematically reviewed to assess progress in LC-MS/MS and define the potential and benefits of matrix-assisted laser desorption/ionization-time-of-flight MS (MALDI-ToF-MS) technology for allergen analysis. MALDI-ToF-MS of initially intact protein is already applied to verify in silico-derived peptide sequences for LC-MS/MS analysis. We describe the origins of MALDI and its future perspectives, including affinity bead-assisted assays coupled to MALDI. Based on the proliferation of reliable and reproducible MALDI-based clinical applications, the technique should emulate the detection capability (sensitivity) of established allergen detection techniques, whilst reducing technical support and having equivalent multiplexing potential to competing techniques, for example, LC-MS/MS and ELISA. Although unlikely to offer inherent SI traceability, MALDI-based allergen analysis will complement existing MS approaches for allergens. Affinity bead-MALDI appears capable of higher throughput at lower cost per sample than almost any existing technique, enabling repeated sub-sampling as a way to reduce representative sampling issues.

Allergenicity of wheat protein in diet: Mechanisms, modifications and challenges

Wheat is widely available in people's daily diets. However, some people are currently experiencing IgE-mediated allergic reactions to wheat-based foods, which seriously impact their quality of life. Thus, it is imperative to provide comprehensive knowledge and effective methods to reduce the risk of wheat allergy (WA) in food. In the present review, recent advances in WA symptoms, the major allergens, detection methods, opportunities and challenges in establishing animal models of WA are summarized and discussed. Furthermore, an updated overview of the different modification methods that are currently being applied to wheat-based foods is provided. This study concludes that future approaches to food allergen detection will focus on combining multiple tools to rapidly and accurately quantify individual allergens in complex food matrices. Besides, biological modification has many advantages over physical or chemical modification methods in the development of hypoallergenic wheat products, such as enzymatic hydrolysis and fermentation. It is worth noting that using biotechnology to edit wheat allergen genes to produce allergen-free food may be a promising method in the future which could improve the safety of wheat foods and the health of allergy sufferers.

Research progress on the allergic mechanism, molecular properties, and immune cross-reactivity of the egg allergen Gal d 5

Eggs and their products are commonly consumed in food products worldwide, and in addition to dietary consumption, egg components are widely used in the food industry for their antimicrobial, cooking, and other functional properties. Globally, eggs are the second most common allergenic food after milk. However, current research on egg allergy primarily focuses on egg white allergens, while research on egg yolk allergens is not comprehensive enough. Therefore, summarizing and analyzing the important allergen α-livetin in egg yolk is significant in elucidating the mechanism of egg allergy and exploring effective desensitization methods. This paper discusses the incidence, underlying mechanism, and clinical symptoms of egg allergy. This article provides a comprehensive summary and analysis of the current research status concerning the molecular structural properties, epitopes, and immune cross-reactivity of the egg yolk allergen, Gal d 5. Additionally, it examines the effects of various processing methods on egg allergens. The article also offers suggestions and outlines potential future research directions and ideas in this field.

Study on the Sensitization and Antigenic Epitopes of Tropomyosin from Antarctic Krill (Euphausia superba)

Antarctic krill (Euphausia superba), a shrimp-like marine crustacean, has become a beneficial source of high-quality animal protein. Meanwhile, a special focus has been placed on its potential sensitization issue. In this study, a 35 kDa protein was purified and identified to be Antarctic krill tropomyosin (AkTM) by high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The purified TM showed a strong IgE-binding capacity to shrimp/crab-allergic patients' sera, indicating that TM is the primary allergen in Antarctic krill. Simulated gastrointestinal digestion revealed that the digestion stability of TM to pepsin was higher than that to trypsin. The strong degranulation triggered by TM in RBL-2H3 cells suggested that AkTM has a strong sensitization capacity. The TM-sensitized BALB/c mice displayed severe anaphylactic symptoms; high levels of TM-specific IgE, sIgG1, and histamine; and increased IL-4, indicating that AkTM could provoke IgE-mediated allergic reactions. Bioinformatics prediction, indirect competition ELISA, and mast cell degranulation assay were used to map the antigenic epitopes of AkTM. Finally, nine peptides of T_43-58, T_88-101, T_111-125, T_133-143, T_144-155, T_183-197, T_223-236, T_249-261, and T_263-281 were identified as the linear epitopes of AkTM. The findings may help us develop efficient food processing techniques to reduce krill allergy and gain a deeper comprehension of the allergenicity of krill allergens.

Epitope Mapping of Lysozyme Using the Chinese Egg-Allergic Sera at Both Pooled and Individual Levels

To accurately map the B-cell linear epitopes of lysozyme (LYS) in eggs, five bioinformatics tools were first used to obtain the mimotopes. Afterward, based on the Chinese egg-allergic sera samples screened by the indirect enzyme-linked immunosorbent, the epitopes possessing the capability of binding to IgG/IgE were mapped at both pooled and individual levels by using overlapping peptides covering the complete amino acid sequence of LYS. Six B-cell linear epitopes and two dominant B-cell linear epitopes that could bind to LYS-sIgG were mapped for the first time. Seven IgE-binding epitopes and three dominant IgE-binding epitopes were also obtained. Furthermore, AA31-34 and AA88-91 were the shared dominant epitopes of LYS-sIgG and LYS-sIgE at pooled and individual levels. Overall, the mapped B-cell linear epitopes filled in the gaps in the study of LYS epitopes, and the results may provide theoretical support for the following immunotherapy of egg allergy.

Effects of covalent conjugation with quercetin and its glycosides on the structure and allergenicity of Bra c p from bee pollen

Profilin family members are potential pan-allergens in foods, presenting public health hazards. However, studies on the allergenicity modification of profilin allergens are limited. Herein, quercetin and its glycosides (isoquercitrin and rutin) were applied to modify the allergenicity of a profilin allergen (Bra c p) from Brassica campestris bee pollen. Results showed that only quercetin can be closely covalently bound to Bra c p among the three, and the binding site was located at the Cys98 residue. After covalently conjunction, the relative content of α-helix structure in Bra c p was reduced by 40.05%, while random coil was increased by 42.89%; moreover, the Tyr and Phe residues in Bra c p were masked. These structural changes could alter the conformational antigenic epitopes of Bra c p, resulting in its allergenicity reduction. Our findings might provide a technical foundation for reducing the allergenicity of bee pollen and foods containing profilin family allergens.

Insight into the IgE-binding sites of allergenic peptides of tropomyosin in shrimp (Penaeus chinensis) induced by cold plasma active particles

Tropomyosin (TM) is a major allergen in crustaceans, and its allergenicity mainly depends on epitopes. In this study, the locations of IgE-binding sites between plasma active particles and allergenic peptides of TM in shrimp (Penaeus chinensis) during cold plasma (CP) treatment were explored. Results showed that the IgE-binding ability of two critical peptides (P1 and P2) increased and then decreased by 9.97 % and 19.50 % after 15 min of CP treatment. It was the first time to show that the contribution rate of target active particles was •O > e_(aq)^- > •OH for reducing IgE-binding ability by 23.51 %-45.40 %, and the contribution rates of other long-lived particles including NO₃^- and NO₂^- was about 54.60 %-76.49 %. In addition, Glu131 and Arg133 in P1 and Arg255 in P2 were certified as the IgE sites. These results were helpful for accurately controlling TM allergenicity, shedding more light on allergenicity mitigation during food processing.

Peanut Allergenicity: An Insight into Its Mitigation Using Thermomechanical Processing

Peanuts are the seeds of a legume crop grown for nuts and oil production. Peanut allergy has gained significant attention as a public health issue due to its increasing prevalence, high rate of sensitization, severity of the corresponding allergic symptoms, cross-reactivity with other food allergens, and lifelong persistence. Given the importance of peanuts in several sectors, and taking into consideration the criticality of their high allergic potential, strategies aiming at mitigating their allergenicity are urgently needed. In this regard, most of the processing methods used to treat peanuts are categorized as either thermal or thermomechanical techniques. The purpose of this review is to provide the reader with an updated outlook of the peanut’s allergens, their mechanisms of action, the processing methods as applied to whole peanuts, as well as a critical insight on their impact on the allergenicity. The methods discussed include boiling, roasting/baking, microwaving, ultrasonication, frying, and high-pressure steaming/autoclaving. Their effectiveness in alleviating the allergenicity, and their capacity in preserving the structural integrity of the treated peanuts, were thoroughly explored. Research data on this matter may open further perspectives for future relevant investigation ultimately aiming at producing hypoallergenic peanuts.

Crystal Structure Analysis of Sarcoplasmic-Calcium-Binding Protein: An Allergen in Scylla paramamosain

The structure of allergenic proteins provides important information about the binding of allergens to antibodies. In this study, the crystal structure of Scy p 4 with a resolution of 1.60 Å was obtained by X-ray diffraction. Epitope mapping of Scy p 4 revealed that linear epitopes are located on the surface of Scy p 4. Also, conformational epitopes are mostly located in the structural conservative region. Further structural comparison, surface electrostatic potential, and hydrogen bond force analysis showed that mutation of Asp₇₀ and Asp_18/20/70 would lead to calcium-binding capacity being lost and destruction of allergenicity. Furthermore, a comparative analysis of structure showed that sarcoplasmic-calcium-binding protein (SCP) had high sequence, secondary, and spatial structural identity in crustaceans, which may be an important factor leading to cross-reactivity among crustaceans. The structure of Scy p 4 provides a template for epitope evaluation and localization of SCPs, which will help to reveal cross-reactivity among species.

Alteration of the allergenicity of cow's milk proteins using different food processing modifications

Milk is an essential source of protein for infants and young children. At the same time, cow's milk is also one of the most common allergenic foods causing food allergies in children. Recently, cow's milk allergy (CMA) has become a common public health issue worldwide. Modern food processing technologies have been developed to reduce the allergenicity of milk proteins and improve the quality of life of patients with CMA. In this review, we summarize the main allergens in cow's milk, and introduce the recent findings on CMA responses. Moreover, the reduced effects and underlying mechanisms of different food processing techniques (such as heating, high pressure, γ-ray irradiation, ultrasound irradiation, hydrolysis, glycosylation, etc.) on the allergenicity of cow's milk proteins, and the application of processed cow's milk in clinical studies, are discussed. In addition, we describe the changes of nutritional value in cow's milk treated by different food processing technologies. This review provides an in-depth understanding of the allergenicity reduction of cow's milk proteins by various food processing techniques.

Identification of the Immunoglobulin E Epitope of Arginine Kinase, an Important Allergen from Crassostrea angulata

Arginine kinase (AK) was identified as an allergen in Crassostrea angulata. However, little information is available about its epitopes. In this study, AK from C. angulata was registered to the World Health Organization/International Union of Immunological Societies allergen nomenclature committee to be named as Cra a 2. The immunoglobulin G/immunoglobulin E-binding capacity of Cra a 2 was significantly reduced after chemical denaturation treatment. Further, eight linear mimotopes and five conformational mimotopes of Cra a 2 were obtained using phage panning. In addition to six linear epitopes that have been identified, two linear epitopes were verified by a synthetic peptide, of which L-Cra a 2-2 was conserved in shellfish. Four conformational epitopes were verified by site-directed mutation, among which mutation of C-Cra a 2-1 affected the structure and reduced the immunoreactivity of Cra a 2 most significantly. Overall, the identified epitopes may lay a foundation for the development of hypoallergenic oyster products through food processing.

Characterization, Epitope Identification, and Cross-reactivity Analysis of Tropomyosin: An Important Allergen of Crassostrea angulata

Oyster is a common shellfish product in China, which is associated with food allergy. However, there is still lack of research on allergens in oysters. In this study, tropomyosin (TM), an important allergen of Crassostrea angulata, was purified and identified by mass spectrometry. Subsequently, TM was cloned and expressed, with a sequence of size 852 bp, encoding 284 amino acid residues. The results of circular dichroism, digestion assay, inhibition enzyme-linked immunosorbent assay, and basophil activation test showed that recombinant TM had similar physicochemical properties and immunological properties to native TM. Furthermore, two conformational mimotopes were obtained and 10 IgE linear epitopes were verified. Meanwhile, different degrees of cross-reactivity were observed between C. angulata TM and the other 8 shellfish TMs using antibodies and serological analysis, which may relate to the 3 conserved epitope regions. These findings are expected to provide a theoretical basis for the molecular diagnosis of oyster allergy and cross-reactivity among shellfish.

Identification of Major B-Cell Linear Epitopes of Peach Allergen Pru p 3 Using Immune Slot-Blot Microarray Assay

Pru p 3, one of the most representative proteins of the lipid transfer proteins (LTPs), is responsible for clinical allergic reactions to food of peach origin. The identification of Pru p 3 epitopes is not comprehensive due to different methods and principles of epitope screening. In addition, evaluation of the stability of the epitopes and the validation of the immunological key amino acids still need further research. Therefore, in the present study, an immune slot-blot microarray assay was performed to screen the epitopes from Pru p 3 overlapping peptide library, and a new epitope (P-1, AA1-16, ITCGQVSSALAPCIPY) was identified and two identified epitopes were deeply investigated (P-2, AA12-27, PCIPYVRGGGAVPPAC; P-3, AA23-38, VPPACCNGIRNVNNLA). The stability of these epitopes was then verified by thermal processing treatment and digestion experiments. Moreover, the key amino acids of the three identified epitopes were obtained by epitope amino acid mutation combined with slot-blot experiments. These findings may contribute to the further understanding of Pru p 3 and the prevention of peach allergy.

Physicochemical characterization and linear epitopes identification of arginine kinase allergen from Crassostrea gigas

BACKGROUND

Molluscan shellfish, including oysters, often cause allergic reactions in sensitive people throughout the world. It has been demonstrated that arginine kinase (AK) is one of the major allergens of oyster. The present study aimed to evaluate the immunoreactivity and structure of oyster AK as affected by heat treatment, pH change, and in vitro digestion. What is more, the immunoglobulin E-binding epitopes of this allergen were also predicted and validated.

RESULTS

Thermal and pH assays revealed that AK was unstable at temperature >40 °C or pH ≤5.0 by sodium dodecyl sulfate polyacrylamide gel electrophoresis and circular dichroism, and the digestibility assays suggested that AK was more easily digested by pepsin than by trypsin and chymotrypsin. The potential epitopes were predicted through immunoinformatics tools, and seven linear epitopes were identified by indirect competition enzyme-linked immunosorbent assay with pooled sera and individual serum from oyster-allergic patients. The critical amino acids in each epitope were also confirmed using mutant peptides. These linear epitopes and critical amino acids were apt to distribute on the outer surface of homology-based AK model. Moreover, the three denaturants (sodium dodecyl sulfate, β-mercaptoethanol, and urea) can destroy the spatial structure of AK and increase or reduce its allergenicity by denaturation treatments.

CONCLUSION

Processing conditions lay the foundation for the variation of allergenicity. Seven linear epitopes and their critical amino acids were identified by indirect competitive enzyme-linked immunosorbent assay. These findings will be helpful in allergy diagnosis and development of hypoallergenic products in the near future. © 2021 Society of Chemical Industry.

Through the Looking Glass: Genome, Phenome, and Interactome of Salmonella enterica

This review revisits previous concepts on biological phenomenon contributing to the success of the Salmonella enterica subspecies I as a pathogen and expands upon them to include progress in epidemiology based on whole genome sequencing (WGS). Discussion goes beyond epidemiological uses of WGS to consider how phenotype, which is the biological character of an organism, can be correlated with its genotype to develop a knowledge of the interactome. Deciphering genome interactions with proteins, the impact of metabolic flux, epigenetic modifications, and other complex biochemical processes will lead to new therapeutics, control measures, environmental remediations, and improved design of vaccines.

Isolation and allergenicity evaluation of glycated α-lactalbumin digestive products and identification of allergenic peptides

This study aimed to isolate and evaluate the allergenicity of glycated α-lactalbumin (ALA) digestive products and identify its allergenic peptides. The digestive products of native-, alone glycated- and ultrasound-assisted glycated ALA (ALA-D, ALA-gal-D, 100ALA-gal-D) were isolated into three fractions (F1, F2 and F3). High-resolution mass spectrometry showed that the digestion-resistant peptides of F2 and F3 mainly distributed in amino acid sequence (AA) 25-31, AA32-53, AA40-53, AA54-60, AA80-90, AA94-104. The allergenicity of the three fractions of glycated ALA was lower than that in ALA-D, indicating glycation of ALA could indeed reduce its allergenicity after digestion. Furthermore, most fractions isolated from high glycation-degree ALA had the lowest allergenicity. The IgG/IgE binding abilities of synthesized peptides indicated that AA94-104 firstly identified by us embodied the strongest allergenicity and might be the potential allergenic peptide. This will provide a theory for preparing hypoallergenic products based on the identified allergenic peptides.

A new paradigm to search for allergenic proteins in novel foods by integrating proteomics analysis and in silico sequence homology prediction: Focus on spirulina and chlorella microalgae

Since novel nutrient sources with high protein content, such as yeast, fungi, bacteria, algae, and insects, are increasingly introduced in the consumer market, safety evaluation studies on their potentially allergenic proteins are required. A pipeline for in silico establishing the sequence-based homology between proteins of spirulina (Arthrospira platensis) and chlorella (Chlorella vulgaris) micro-algae and those included in the AllergenOnline (AO) database (AllergenOnline.org) is described. The extracted proteins were first identified through tryptic peptides analysis by reversed-phase liquid chromatography and high resolution/accuracy Fourier-transform tandem mass spectrometry (RPLC-ESI-FTMS/MS), followed by a quest on the UniProt database. The AO database was subsequently interrogated to assess sequence similarity between identified microalgal proteins and known allergens, based on criteria established by the World Health Organization (WHO) and Food and Agriculture Organization (FAO). A direct search for microalgal proteins already included in allergen databases was also performed using the Allergome database. Six proteins exhibiting a significant homology with food allergens were identified in spirulina extracts. Five of them, i.e., two thioredoxins (D4ZSU6, K1VP15), a superoxide dismutase (C3V3P3), a glyceraldehyde-3-phosphate dehydrogenase (K1W168), and a triosephosphate isomerase (D5A635), resulted from the search on AO. The sixth protein, C-phycocyanin beta subunit (P72508), was directly obtained after examining the Allergome database. Two proteins exhibiting significant sequence homology with food allergens were retrieved in chlorella extracts, viz. calmodulin (A0A2P6TFR8), which is related to troponin c (D7F1Q2), and fructose-bisphosphate aldolase (A0A2P6TDD0). Specific serum screenings based on immunochemical tests should be undertaken to confirm or rule out the allergenicity of the identified proteins.

Two hypo-allergenic derivatives lacking the dominant linear epitope of Scy p 1 and Scy p 3

Scylla paramamosain frequently elicits IgE-mediated type-I hypersensitivity reactions. Molecular candidates for crab allergen-specific immunotherapy have not been studied previously. In this study, reduced and alkylated (red/alk) derivatives with destroyed conformational epitopes and mutant derivatives (mtALLERGEN) with deleted heat/digestion-stable linear epitopes were produced of tropomyosin and myosin light chain. Structural changes and the allergenicity of derivatives was analyzed. Compared with wild-type allergens, red/alk derivatives had dramatically altered protein structures, whereas mtALLERGEN showed slightly structural effects. Enzyme linked immunosorbent assay revealed the heterogeneous epitope-recognition patterns with derivatives among 29 crab-sensitised patients, of whom 13% and 62% recognised conformational and linear epitopes, respectively, whereas 25% recognised both epitope types to the same extent. Furthermore, mtALLERGEN could not bind to IgE or induce basophil activation in some patients. These results imply that hypo-allergenic derivatives of crab myofibril allergens that specifically lacked linear epitopes may serve as viable candidates for immunotherapy.

Reduction in Allergenicity and Induction of Oral Tolerance of Glycated Tropomyosin from Crab

Tropomyosin (TM) is an important crustacean (Scylla paramamosain) allergen. This study aimed to assess Maillard-reacted TM (TM-G) induction of allergenic responses with cell and mouse models. We analyzed the difference of sensitization and the ability to induce immune tolerance between TM and TM-G by in vitro and in vivo models, then we compared the relationship between glycation sites of TM-G and epitopes of TM. In the in vitro assay, we discovered that the sensitization of TM-G was lower than TM, and the ability to stimulate mast cell degranulation decreased from 55.07 ± 4.23% to 27.86 ± 3.21%. In the serum of sensitized Balb/c mice, the level of specific IgE produced by TM-G sensitized mice was significantly lower than TM, and the levels of interleukins 4 and interleukins 13 produced by Th2 cells in spleen lymphocytes decreased by 82.35 ± 5.88% and 83.64 ± 9.09%, respectively. In the oral tolerance model, the ratio of Th2/Th1 decreased from 4.05 ± 0.38 to 1.69 ± 0.19. Maillard reaction masked the B cell epitopes of TM and retained some T cell epitopes. Potentially, Maillard reaction products (MRPs) can be used as tolerance inducers for allergen-specific immunotherapy.

Crystal Structure Analysis and IgE Epitope Mapping of Allergic Predominant Region in Scylla paramamosain Filamin C, Scy p 9

Filamin C (FLN c) is a novel allergen in shellfish. In this study, FLN c from Scylla paramamosain was divided into three regions for recombinant expression based on the number of domains and amino acids. Using dot blot and basophil activation tests, the allergic predominant region of FLN c was determined to be 336-531 amino acid positions (named FLN c-M). It was confirmed that by X-ray diffraction, the crystal structure of FLN c-M with immunoglobulin-like folding at a resolution of 1.7 Å was obtained. The monomer was a barrel structure composed of 16 β-strands and 2 α-helices. Three conformational epitopes were predicted, six linear epitopes were verified by serological test, and they were positioned on the crystal structure of FLN c-M. For the first time, the crystal structure of the allergic predominant region of FLN c was determined, and it provided an accurate template for the localization of IgE epitopes.

A Combined Proteomic and Metabolomic Strategy for Allergens Characterization in Natural and Fermented Brassica napus Bee Pollen

Bee pollen is consumed for its nutritional and pharmacological benefits, but it also contains hazardous allergens which have not been identified. Here, we identified two potential allergens, glutaredoxin and oleosin-B2, in Brassica napus bee pollen using mass spectrometry-based proteomics analyses, and used bioinformatics to predict their antigenic epitopes. Comparison of fermented (by Saccharomyces cerevisiae) and unfermented bee pollen samples indicated that glutaredoxin and oleosin-B2 contents were significantly decreased following fermentation, while the contents of their major constituent oligopeptides and amino acids were significantly increased based on metabolomics analyses. Immunoblot analysis indicated that the IgE-binding affinity with extracted bee pollen proteins was also significantly decreased after fermentation, suggesting a reduction in the allergenicity of fermented bee pollen. Furthermore, fermentation apparently promoted the biosynthesis of L-valine, L-isoleucine, L-tryptophan, and L-phenylalanine, as well as their precursors or intermediates. Thus, fermentation could potentially alleviate allergenicity, while also positively affecting nutritional properties of B. napus bee pollen. Our findings might provide a scientific foundation for improving the safety of bee pollen products to facilitate its wider application.

Epitope mapping and the effects of various factors on the immunoreactivity of main allergens in egg white

Egg white has high protein content and numerous biological/functional properties. However, reported allergenicity for some of the proteins in egg white is an issue that needs to be paid exclusive attention. A consideration of the structure of IgE epitopes and their sequences, as well as a comprehensive understanding of the effects of various processes on epitopes and the impact of the gastrointestinal tract on them, can help target such issues. The current study focuses on the identified IgE epitopes in egg white proteins and evaluation of the effects of the gastrointestinal digestion, carbohydrate moiety, food matrix, microbial fermentation, recombinant allergen, heat treatment, Maillard reaction and combination of various processes and gastrointestinal digestion on egg white allergenicity. Although the gastrointestinal tract reduces the immunoreactivity of native egg white proteins, some of the IgE epitope-containing fragments remain intact during the digestion process. It has been found that the gastrointestinal tract can have both positive and negative impacts on the IgE binding activities of egg white proteins. Elimination of the carbohydrate moiety leads to a reduction in the immunoreactivity of ovalbumin. But, such effects from the carbohydrate parts in the IgE binding activity need to be explored further. In addition, the interaction between the egg white proteins and the food matrix leads to various effects from the gastrointestinal tract on the digestion of egg white proteins and their subsequent immunoreactivity. Further on this matter, studies have shown that both microbial fermentation and Maillard reaction can reduce the IgE binding activities of egg white proteins. Also, as an alternate approach, the thermal process can be used to treat the egg white proteins, which may result in the reduction or increase in their IgE binding activities depending on the conditions used in the process. Overall, based on the reported data, the allergenicity levels of egg white proteins can be mitigated or escalated depending on the conditions applied in the processing of the food products containing egg white. So far, no practical solutions have been reported to eliminate such allergenicity.

An overview of tropomyosin as an important seafood allergen: Structure, cross-reactivity, epitopes, allergenicity, and processing modifications

Tropomyosin (TM) is a major allergen in crustaceans, which often causes allergy and is fatal to some consumers. Currently, the most effective treatment is to avoid ingesting TM, although most adverse events occur in accidental ingestion. In this review, the molecular characterization, epitopes, cross-reactivity, and pathogenesis of TM are introduced and elucidated. Modification of TM by traditional processing methods such as heat treatment and enzymatic hydrolysis, and innovative processing technologies including high-pressure treatment, cold plasma (CP), ultrasound, pulsed electric field (PEF), pulsed ultraviolet, microwave and irradiation are discussed in detail. Particularly, enzymolysis, PEF, and CP technologies show great potential for modifying TM and more studies are needed to verify their effectiveness for the seafood industry. Possible mechanisms and the advantages/disadvantages of these technologies for the mitigation of TM allergenicity are also highlighted. Further work should be conducted to investigate the allergenicity caused by protein segments such as epitopes, examine the interaction sites between the allergen and the processing techniques and reveal the reduction mechanism of allergenicity.

Understanding memory B cell selection

The mammalian adaptive immune system has evolved over millions of years to become an incredibly effective defense against foreign antigens. The adaptive immune system's humoral response creates plasma B cells and memory B cells, each with their own immunological objectives. The affinity maturation process is widely viewed as a heuristic to solve the global optimization problem of finding B cells with high affinity to the antigen. However, memory B cells appear to be purposely selected earlier in the affinity maturation process and have lower affinity. We propose that this memory B cell selection process may be an approximate solution to two optimization problems: optimizing for affinity to similar antigens in the future despite mutations or other minor differences, and optimizing to warm start the generation of plasma B cells in the future. We use simulations to provide evidence for our hypotheses, taking into account data showing that certain B cell mutations are more likely than others. Our findings are consistent with memory B cells having high-affinity to mutated antigens, but do not provide strong evidence that memory B cells will be more useful than selected naive B cells for seeding the secondary germinal centers.

Reducing the Allergenicity of Shrimp Tropomyosin and Allergy Desensitization Based on Glycation Modification

Shrimp is a major allergic food that could trigger severe food allergy, with the most significant and potent allergen of shrimp referred to as tropomyosin (TM). Glycation modification (Maillard reaction) could reportedly weaken the allergenicity of TM and generate hypoallergenic TM, while up to now, there is still a lack of investigations on the hypoallergenic glycated tropomyosin (GTM) as a candidate immunotherapy for desensitizing the shrimp TM-induced allergy. This study analyzed the effects of glycation modification on decreasing the allergenicity of TM and generated hypoallergenic GTM and how GTM absorbed to the Al(OH)₃ function as a candidate immunotherapy for desensitizing allergy. As the results, in comparison to TM, the saccharides of smaller molecular sizes could lead to more advanced glycation end products in GTMs than saccharides of greater molecular sizes, and TM glycated by saccharides of different molecular sizes (glucose, maltose, maltotriose, maltopentaose, and maltoheptaose) exhibited lower allergenicity as a hypoallergen upon activating the allergic reactions of the mast cell and mouse model, while TM glycated by maltose had insignificant allergenicity changes upon activating the allergic reactions of the mast cell and mouse model. In addition, the hypoallergenic GTM + Al(OH)₃ was efficient as a candidate immunotherapy; this work intended to offer preclinical data to promote GTM + Al(OH)₃ as a candidate allergen-specific immunotherapy for desensitizing the allergy reactions for patients allergic to shrimp food.

Feasibility of atmospheric cold plasma for the elimination of food hazards: Recent advances and future trends

In recent decades, food safety has emerged as a worldwide public health issue with economic and political implications. Pesticide residues, mycotoxins, allergens, and antinutritional factors are the primary concerns associated with food products due to their potential adverse health effects. Although various conventional processing methods (such as washing, peeling, and cooking) have been used to reduce or eliminate these hazards from agricultural food materials, the results obtained are not quite satisfactory. Recently, atmospheric cold plasma (ACP), an emerging low -temperature and green processing technology, has shown great potential for mitigating food hazards. However, detailed descriptions of the effects of ACP treatment on food hazards are still not available. Thus, the current review aims to highlight recent studies on the efficacy and application of ACP in the reduction or elimination of pesticide residues, mycotoxins, allergens, and antinutritional factors in various food products. The possible working mechanisms of ACP and its effect on food quality, and the toxicity of degradation products are emphatically discussed. In addition, multiple factors affecting the efficacy of ACP are summarized in detail. At the same time, the major technical challenges for practical application and future development prospects of this emerging technology are also highlighted.

Enzymatic crosslinking and food allergenicity: A comprehensive review

Food allergy has become a major global public health concern. In the past decades, enzymatic crosslinking technique has been employed to mitigate the immunoreactivity of food allergens. It is an emerging non-thermal technique that can serve as a great alternative to conventional food processing approaches in developing hypoallergenic food products, owing to their benefits of high specificity and selectivity. Enzymatic crosslinking via tyrosinase (TYR), laccase (LAC), peroxidase (PO), and transglutaminase (TG) modifies the structural and biochemical properties of food allergens that subsequently cause denaturation and masking of the antigenic epitopes. LAC, TYR, and PO catalyze the oxidation of tyrosine side chains to initiate protein crosslinking, while TG initiates isopeptide bonding between lysine and glutamine residues. Enzymatic treatment produces a high molecular weight crosslinked polymer with reduced immunoreactivity and IgE-binding potential. Crosslinked allergens further inhibit mast cell degranulation due to the lower immunostimulatory potential that assists in the equilibration of T-helper (Th)1/Th2 immunobalance. This review provides an updated overview of the studies carried out in the last decade on the potential application of enzymatic crosslinking for mitigating food allergenicity that can be of importance in the context of developing hypoallergenic/non-allergenic food products.

IgE epitope analysis of sarcoplasmic-calcium-binding protein, a heat-resistant allergen in Crassostrea angulata

Sarcoplasmic-calcium-binding protein (SCP) has been investigated as a novel allergen in Crassostrea angulata. Nevertheless, knowledge of its effector-cell-based allergic relevance and epitopes is limited. In this study, the heat-resistant allergen SCP was able to induce significant upregulation of CD63 and CD203c (p < 0.05), which showed obvious allergenicity in a basophil activation test. Furthermore, immunoinformatic tools, a one-bead-one-compound peptide library, and phage display technology were combined to analyze the allergenic epitopes of SCP. Five linear epitopes named L-SCP-1 (AA22-33), L-SCP-2 (AA64-75), L-SCP-3 (AA80-90), L-SCP-4 (AA107-116), and L-SCP-5 (AA144-159) were verified using serological tests. Additionally, two conformational epitopes (C-SCP-1 and C-SCP-2) were determined, and C-SCP-1 was located at one of the calcium-binding sites (AA106-117). Moreover, SCP showed weaker typical α-helical features and higher hydrophobicity after Ca2+ depletion, which reduced its IgE-binding capacity. Overall, these epitope data could enhance our understanding of oyster allergens, which could be used to develop hypoallergenic shellfish products.

Processes for reducing egg allergenicity: Advances and different approaches

Egg is a versatile ingredient and ubiquitous food. Nevertheless, egg proteins are a common cause of allergy mainly in childhood. Until now, egg eviction has been the best way to prevent this disorder, however, processed food can contribute to mitigate allergies and to guarantee life quality of allergic individuals. This review focuses on discussing and highlighting recent advances in processes to reduce egg allergenicity as well as new approaches to egg allergy management. In recent times, different methods have been developed to reduce egg allergies, by hiding the epitopes or changing the native or conformational structure of the proteins. Despite processing food has not yet been a solution to completely remove the allergenic potential of egg proteins, innovative strategies, such as addition of phenolic compounds, have been developed with promising results.

Characterization of the protein structure of soymilk fermented by Lactobacillus and evaluation of its potential allergenicity based on the sensitized-cell model

This study aimed to investigate the effects of fermented soymilk (FSM) with Lactobacillus brevis CICC 23,474 and L. brevis CICC 23,470 on the structural changes and allergenicity of major allergenic proteins in soymilk (SM). Spectroscopy and liquid chromatograph-tandem mass spectrometer (LC-MS/MS) were used to characterize changes in protein spatial structure and epitopes. The antigenicity and potential allergenicity were evaluated by immunoblotting, enzyme-linked immunosorbent assay (ELISA) and KU812 cell degranulation assay. Results suggested that the advanced structure of proteins was destroyed. Antigenicity was also significantly reduced, and five human IgE-binding linear epitopes (i.e., E5-E33, R27-S41, D414-A437, G253-I265 and V449-S471) were destroyed by fermentation. Furthermore, after in vitro simulated gastrointestinal digestion, FSM showed lower IgG/IgE-binding capacity and weaker degranulation ability of KU812 cells. All these findings demonstrated that fermentation with Lactobacillus can destroy the conformational and linear epitopes of proteins and reduce the potential allergenicity of SM.

Components of plant-derived food allergens: Structure, diagnostics, and immunotherapy

A large number of plant-derived food allergen components have been identified to date. Although these allergens are diverse, they often share common structural features such as numerous disulfide bonds or oligomeric structures. Furthermore, some plant-derived food allergen components cross-react with pollen allergens. Since the relationship between allergen components and clinical symptoms has been well characterized, measurements of specific IgE to these components have become useful for the accurate clinical diagnosis and selection of optimal treatment methods for various allergy-related conditions including allergy caused by plant-derived foods. Herein, I have described the types and structures of different plant allergen components and outlined the diagnosis as well as treatment strategies, including those reported recently, for such substances. Furthermore, I have also highlighted the contribution of allergen components to this field.

Structural Phylogeny of Different Allergens May Reveal Common Epitopic Footprint

BACKGROUND

The incidence of allergy is increasing at an alarming rate for the last few decades.

OBJECTIVE

Our present study is focused on finding out the structurally homologous motifs present in different proteinaceous allergens Methods: Significant number of protein sequences and their corresponding structures of various pollen, fungal, bacterial, and food allergens were retrieved, and the sequence and structural identity were analyzed.

RESULTS

Intra- and inter-sequence and their structural analysis of the proteinaceous allergens, resulted in no significant relationships among them. A few, but not negligible number of high structural similarities were observed within different groups of allergens from fungus, angiosperms, and animals (Aves and Mammalia).

CONCLUSION

Our in silico study on thirty-six different allergens showed a significant level of structural similarities among themselves, regardless of their sequences.

Identification and Amino Acid Analysis of Allergenic Epitopes of a Novel Allergen Paramyosin (Rap v 2) from Rapana venosa

Besides tropomyosin (TM) that is widely recognized as a major allergen in molluscs, a 99-kDa novel allergen (Rap v 2) was recently found in the sea snail Rapana venosa and identified as paramyosin (PM). However, the allergenic epitopes of PM in any molluscs have not been identified yet. In the present study, seven allergenic epitopes of Rap v 2 were identified by immunoinformatics tools, dot-blot inhibition assay, and basophil degranulation assay. Based on the analysis of PM and allergenic epitope amino acids, it was found that highly hydrophobic and positively charged amino acid residues play an important role in the formation of Rap v 2 epitopes. In addition, three potential critical amino acids that may account for TM and PM cross-reactivity in molluscs were found by sequence- and structure-based methods. These findings could be of major importance for improving the understanding of relevant paramyosin epitopes and the prevention and therapy of mollusc allergy.

Combination Processing Method Reduced IgE-Binding Activity of Litopenaeus vannamei by Modifying Lysine, Arginine, and Cysteine on Multiple Allergen Epitopes

Allergic reactions occur after the whole food is ingested, rather than the purified allergen. The present study explores the low-allergenic food processing for Litopenaeus vannamei by analysis of macrostructure, digestibility, and immunoreactivity. Furthermore, the presence of modified amino acids on the reported IgE epitopes was analyzed by mass spectrometry. Results showed that the combination processing of Maillard reaction (shrimp meat with galactose) with high temperature-pressure at 115 °C obviously changed the macrostructure and increased the digestibility for the shrimp meat. Meanwhile, the processing significantly reduced the IgG/IgE-binding activity of the shrimp meat. The hypo-IgE-binding activity in processed shrimp may be due to the modification of lysine, arginine, and cysteine residues in antigen epitopes. This is a comprehensive assessment of the specific amino acid residues modified by glycation of multiple allergens in processed L. vannamei, which provides a new research method to explore the hypo-IgE-binding activity in food.