Mutational analysis of the IgE-binding epitopes of P34/Gly m Bd 30K

Legume Allergens Pea, Chickpea, Lentil, Lupine and Beyond

PURPOSE OF THE REVIEW

In the last decade, an increasing trend towards a supposedly healthier vegan diet could be observed. However, recently, more cases of allergic reactions to plants and plant-based products such as meat-substitution products, which are often prepared with legumes, were reported. Here, we provide the current knowledge on legume allergen sources and the respective single allergens. We answer the question of which legumes beside the well-known food allergen sources peanut and soybean should be considered for diagnostic and therapeutic measures.

RECENT FINDINGS

These "non-priority" legumes, including beans, pea, lentils, chickpea, lupine, cowpea, pigeon pea, and fenugreek, are potentially new important allergen sources, causing mild-to-severe allergic reactions. Severe reactions have been described particularly for peas and lupine. An interesting aspect is the connection between anaphylactic reactions and exercise (food-dependent exercise-induced anaphylaxis), which has only recently been highlighted for legumes such as soybean, lentils and chickpea. Most allergic reactions derive from IgE cross-reactions to homologous proteins, for example between peanut and lupine, which is of particular importance for peanut-allergic individuals ignorant to these cross-reactions. From our findings we conclude that there is a need for large-scale studies that are geographically distinctive because most studies are case reports, and geographic differences of allergic diseases towards these legumes have already been discovered for well-known "Big 9" allergen sources such as peanut and soybean. Furthermore, the review illustrates the need for a better molecular diagnostic for these emerging non-priority allergen sources to evaluate IgE cross-reactivities to known allergens and identify true allergic reactions.

Soybean allergy: characteristics, mechanisms, detection and its reduction through novel food processing techniques

Human beings have consumed soybean as an excellent food source for thousand years due to its rich protein, fatty acids, minerals, and fibers. However, soybeans were recognized as one of the big eight allergens resulting in allergic symptoms and even could lead to death. With the increasing demand for soybean products, the challenges caused by soybean allergy need to be solved urgently. This review detailly described the pathogenesis and clinical characteristics of soybean allergy, and also the advantages and disadvantages of four different diagnostic methods were summarized. The major soybean allergens and their structures were summarized. Three types of soybean allergy including Type I, III, and IV, which could trigger allergic reactions were reported in this review. Summary in four different diagnostic methods showed that double-blind, placebo-controlled food challenge is recognized as a gold standard for diagnosing soybean allergy. Three types of processing techniques in reducing soybean allergy were discussed, and the results concluded that some novel food processing techniques such as ultrasound, cold-plasma treatment, showed potential application in the reduction of soybean allergenicity. Further, some suggestions regarding the management and treatment of food allergies were addressed in this review.

Site-directed mutagenesis by biolistic transformation efficiently generates inheritable mutations in a targeted locus in soybean somatic embryos and transgene-free descendants in the T1 generation

The clustered regularly interspaced short palindromic repeat (CRISPR)/CRISPR-associated endonuclease 9 (Cas9) system is being rapidly developed for mutagenesis in higher plants. Ideally, foreign DNA introduced by this system is removed in the breeding of edible crops and vegetables. Here, we report an efficient generation of Cas9-free mutants lacking an allergenic gene, Gly m Bd 30K, using biolistic transformation and the CRISPR/Cas9 system. Five transgenic embryo lines were selected on the basis of hygromycin resistance. Cleaved amplified polymorphic sequence analysis detected only two different mutations in e all of the lines. These results indicate that mutations were induced in the target gene immediately after the delivery of the exogenous gene into the embryo cells. Soybean plantlets (T0 plants) were regenerated from two of the transgenic embryo lines. The segregation pattern of the Cas9 gene in the T1 generation, which included Cas9-free plants, revealed that a single copy number of transgene was integrated in both lines. Immunoblot analysis demonstrated that no Gly m Bd 30K protein accumulated in the Cas9-free plants. Gene expression analysis indicated that nonsense mRNA decay might have occurred in mature mutant seeds. Due to the efficient induction of inheritable mutations and the low integrated transgene copy number in the T0 plants, we could remove foreign DNA easily by genetic segregation in the T1 generation. Our results demonstrate that biolistic transformation of soybean embryos is useful for CRISPR/Cas9-mediated site-directed mutagenesis of soybean for human consumption.

Hypoallergenic mutants of the major oyster allergen Cra g 1 alleviate oyster tropomyosin allergenic potency

Design of hypoallergen with low IgE reactivity is desirable for allergen-specific immunotherapy. Despite oyster tropomyosin (Cra g 1) is considered as the major allergen, no immunotherapy is available now. In the current research, we generated hypoallergens of Cra g 1 and evaluated their allergenicity. Four hypoallergenic derivatives were constructed by epitope deletion or site-directed mutagenesis on grounds of the identified epitopes. They showed obvious reduction in reactivity towards IgE from oyster-allergic patients and Cra g 1-sensitized BN rats, as well as significant decrease in degranulation and secretion of allergic mediators including histamine, IL-4, IL-6 and TNF-α. In addition, to further investigate the molecular mechanism, we examined the effects of these variants on FcεRI-dependent signalling pathway in IgE-challenged RBL-2H3 cells. We found that the hypoallergenic mutants were able to attenuate FcεRI-mediated signaling cascades in tested cells. These results indicate that the hypoallergenic molecules have ideal characteristics and offer a promising new strategy in clinical immunotherapy for shellfish-allergic subjects.

Simultaneous induction of mutant alleles of two allergenic genes in soybean by using site-directed mutagenesis

BACKGROUND

Soybean (Glycine max) is a major protein crop, because soybean protein has an amino acid score comparable to that of beef and egg white. However, many allergens have been identified among soybean proteins. A decrease in allergenic protein levels would be useful for expanding the market for soybean proteins and processed foods. Recently, the CRISPR/Cas9 system has been adopted as a powerful tool for the site-directed mutagenesis in higher plants. This system is expected to generate hypoallergenic soybean varieties.

RESULTS

We used two guide RNAs (gRNAs) and Agrobacterium-mediated transformation for simultaneous site-directed mutagenesis of two genes encoding the major allergens Gly m Bd 28 K and Gly m Bd 30 K in two Japanese soybean varieties, Enrei and Kariyutaka. We obtained two independent T0 Enrei plants and nine T0 Kariyutaka plants. Cleaved amplified polymorphic sequence (CAPS) analysis revealed that mutations were induced in both targeted loci of both soybean varieties. Sequencing analysis showed that deletions were the predominant mutation type in the targeted loci. The Cas9-free plants carrying the mutant alleles of the targeted loci with the transgenes excluded by genetic segregation were obtained in the T2 and T3 generations. Variable mutational spectra were observed in the targeted loci even in T2 and T3 progenies of the same T0 plant. Induction of multiple mutant alleles resulted in six haplotypes in the Cas9-free mutants derived from one T0 plant. Immunoblot analysis revealed that no Gly m Bd 28 K or Gly m Bd 30 K protein accumulated in the seeds of the Cas9-free plants. Whole-genome sequencing confirmed that a Cas9-free mutant had also no the other foreign DNA from the binary vector. Our results demonstrate the applicability of the CRISPR/Cas9 system for the production of hypoallergenic soybean plants.

CONCLUSIONS

Simultaneous site-directed mutagenesis by the CRISPR/Cas9 system removed two major allergenic proteins from mature soybean seeds. This system enables rapid and efficient modification of seed components in soybean varieties.

Technical opinion of the Asociación Mexicana de Gastroenterología on soy plant-based beverages

There has been a recent increase in the consumption of cow's milk substitutes, specifically plant-based beverages, which have erroneously been named "plant milks". Plant-based beverages do not have a standard of identity, and so their nutritional composition can vary from one brand to another, even within the same category. The aim of the present narrative review was to produce a technical opinion to serve as a frame of reference for sustaining the recommendation of soy plant-based beverages. Nutrition and gastroenterology experts that belong to the Asociación Mexicana de Gastroenterología jointly commented on and analyzed themes on plant-based beverages, and on soy drinks in particular, including their nutritional characteristics, consumption in children, and potential growth and development alterations, as well as soy drink consumption in adults and its association with gastrointestinal alterations and other conditions. Plant-based beverages, including those made from soy, are not a replacement for breastmilk or breastmilk substitutes. Soy beverages are considered safe and can enrich the varied diet of its consumers, as long as they are considered an additional liquid portion of the diet. They can be ingested by adults and children above two years of age that present with cow's milk protein allergy or lactose intolerance.

The separation and identification of the residual antigenic fragments in soy protein hydrolysates

Soybean is one of the major food allergens. In this study, soy protein isolate was hydrolyzed by Neutrase and Flavourzyme. The hydrolysates were separated by ultrafiltration and ion-exchange chromatography. The antigenicity of proteins was determined by indirect competitive ELISA. The molecular weight distribution was characterized by SDS-PAGE. The amino acid sequence of chromatography fractions was analyzed by LC-MS. The results showed that proteins with >50 kDa in hydrolysates had the highest antigenicity and were further separated into F1 -F5 fragments by ion-exchange chromatography. Fragment F4 , which was the most antigenic, was analyzed by LC-MS. The results of mass spectrometry showed that most of the peptides that contained antigen epitopes in chromatography fraction F4 belonged to glycinin subunits. The antigenicity of soy protein was reduced by enzymatic hydrolysis, but glycinin showed resistance to enzymatic hydrolysis. PRACTICAL APPLICATIONS: The identification of residual antigenicity in soy protein hydrolysates by LC-MS provides important information on the resistance mechanism of enzymatic hydrolysis of soybean protein allergens. In addition, the efficient separation of soy protein hydrolysates could be beneficial for developing low-allergenic soybean products.

Identification and mutational analysis of continuous, immunodominant epitopes of the major oyster allergen Crag 1

Shellfish, including oysters, often cause allergic reactions in children and adults. Oysters are inevitably consumed because of its delicacy and nutritional benefit, leading to frequent occurrence of severe clinical symptoms observed in patients with oyster hypersensitivity. We aimed to identify the immunodominant epitopes of oyster tropomyosin and crucial amino acids for IgE binding, which will help us to further understand the immunochemical characteristics of Cra g 1. The potential epitopes were predicted by immunoinformatics tools and the resultant immunodominant epitopes were identified by inhibition ELISA with pooled sera and individual serum from oyster allergic patients. Surprisingly, homologous substitution of multiple amino acids led to obviously decrease affinity of IgE antibodies, but this manner did not abrogate binding completely. Five major linear epitopes were evenly distributed on the surface of homology-based Cra g 1 model and hydrophilic residues appeared to be the most important for IgE binding. These results not only offer a better understanding of the molecular mechanism of interaction between Cra g 1 and oyster-specific IgE but also have significance in clinical diagnosis and immunotherapy.

Combining 2-DE immunoblots and mass spectrometry to identify putative soybean (Glycine max) allergens

Soybean is recognized as a commonly allergenic food, but the identity of important allergens is not well studied. Recently, some global regulatory agencies started requiring quantitative analysis of individual allergens, including unproven allergens, as part of the risk assessment for genetically engineered (GE) soybeans. We sought to identify soybean proteins that bind IgE from any of 10 individual soybean-sensitized subjects. Soybean IgE binding proteins were identified by 2-DE immunoblots using sera from four soy-allergic and plasma from six soy-sensitized human subjects. Corresponding spots were excised from stained gels, digested, and analyzed using a quadrupole TOF Synapt G2-S tandem mass spectrometer. Results showed the major IgE binding proteins were subunits of either β-conglycinin (Gly m 5) or glycinin (Gly m 6). Soybean Kunitz trypsin inhibitor (SKTI) was a significant IgE binding protein for four subjects. Soybean agglutinin, seed biotinylated protein (SBP) of 65 kDa, late embryogenesis protein (LEP), and sucrose-binding protein were identified as IgE binding only for soy-sensitized subjects. We conclude that the major soybean allergens are isoforms of Gly m 5, Gly m 6, and possibly SKTI and that requirements for quantitative measurement of proteins that are not clear allergens is not relevant to safety.

A comparative secretome analysis of industrial Aspergillus oryzae and its spontaneous mutant ZJGS-LZ-21

Aspergillus oryzae koji plays a crucial role in fermented food products due to the hydrolytic activities of secreted enzymes. In the present study, we performed a comparative secretome analysis of the industrial strain of Aspergillus oryzae 3.042 and its spontaneous mutantZJGS-LZ-21. One hundred and fifty two (152) differential protein spots were excised (p<0.05), and 25 proteins were identified. Of the identified proteins, 91.3% belonged to hydrolytic enzymes acting on carbohydrates or proteins. Consistent with their enzyme activities, the expression of 14 proteins involved in the degradation of cellulose, hemicellulose, starch and proteins, increased in the ZJGS-LZ-21isolate. In particular, increased levels of acid protease (Pep) may favor the degradation of soy proteins in acidic environments and promote the cleavage of allergenic soybean proteins in fermentation, resulting in improvements of product safety and quality. The ZJGS-LZ-21 isolate showed higher protein secretion and increased hydrolytic activities than did strain 3.042, indicating its promising application in soybean paste fermentation.

Development of soybeans with low P34 allergen protein concentration for reduced allergenicity of soy foods

BACKGROUND

In soybean, at least 16 seed proteins have been identified as causing allergenic reactions in sensitive individuals. As a soybean genebank accession low in the immunodominant protein P34 (Gly m Bd 30K) has recently been found, introgression of the low-P34 trait into adapted soybean germplasm has been attempted in order to improve the safety of food products containing soybean protein. Therefore, marker-assisted selection and proteomics were applied to identify and characterize low-P34 soybeans.

RESULTS

In low-P34 lines selected from a cross-population, concentrations of the P34 protein as identified with a polyclonal antibody were reduced by 50-70% as compared to P34-containing controls. Using 2D electrophoresis and immunoblotting, the reduction of P34 protein was verified in low-P34 lines. This result was confirmed by liquid chromatographic-tandem mass spectrometric analysis, which revealed either a reduction or complete absence of the authentic P34 protein as suggested from presence or absence of a unique peptide useful for discriminating between conventional and low-P34 lines.

CONCLUSION

Marker-assisted selection proved useful for identifying low-P34 soybean lines for the development of hypoallergenic soy foods. The status of the P34 protein in low-P34 lines needs further characterization. In addition, the food safety relevance of low-P34 soybeans should be tested in clinical studies. © 2016 Society of Chemical Industry.

Health Risks and Benefits of Chickpea (Cicer arietinum) Consumption

Chickpeas (CPs) are one of the most commonly consumed legumes, especially in the Mediterranean area as well as in the Western world. Being one of the most nutritional elements of the human diet, CP toxicity and allergy have raised health concerns. CPs may contain various antinutritional compounds, including protease inhibitors, phytic acid, lectins, oligosaccharides, and some phenolic compounds that may impair the utilization of the nutrients by people. Also, high consumption rates of CPs have enhanced the allergic problems in sensitive individuals as they contain many allergens. On the other hand, beneficial health aspects of CP consumption have received attention from researchers recently. Phytic acid, lectins, sterols, saponins, dietary fibers, resistant starch, oligosaccharides, unsaturated fatty acids, amylase inhibitors, and certain bioactive compounds such as carotenoids and isoflavones have shown the capability of lowering the clinical complications associated with various human diseases. The aim of this paper is to unravel the health risks as well as health-promoting aspects of CP consumption and to try to fill the gaps that currently exist. The present review also focuses on various prevention strategies to avoid health risks of CP consumption using simple but promising ways.

Epitope mapping and identification of amino acids critical for mouse IgG-binding to linear epitopes on Gly m Bd 28K

Gly m Bd 28K is one of the major allergens in soybeans, but there is limited information on its IgG-binding epitopes. Thirty-four overlapping peptides that covered the entire sequence of Gly m Bd 28K were synthesized, and 3 monoclonal antibodies against Gly m Bd 28K were utilized to identify the IgG-binding regions of Gly m Bd 28K. Three dominant peptides corresponding to (28)GDKKSPKSLFLMSNS(42)(G28-S42), (56)LKSHGGRIFYRHMHI(70)(L56-I70), and (154)ETFQSFYIGGGANSH(168)(E154-H168) were recognized. L56-I70 is the most important epitope, and a competitive ELISA indicated that it could inhibit the binding of monoclonal antibody to Gly m Bd 28K protein. Alanine scanning of L56-I70 documented that F64, Y65, and R66 were the critical amino acids of this epitope. Two bioinformatics tools, ABCpred and BepiPred, were used to predict the epitopes of Gly m Bd 28K, and the predictions were compared with the epitopes that we had located by monoclonal antibodies.

Cross-reactivity between the soybean protein p34 and bovine caseins

Purpose

Soy-based formulas are widely used as dairy substitutes to treat milk allergy patients. However, reactions to soy have been reported in a small proportion of patients with IgE-mediated milk allergies. The aim of this work was to explore whether P34, a mayor soybean allergen, is involved in this cross-reactivity.

Methods

In vitro recognition of P34 was evaluated by immunoblotting, competitive ELISA and basophil activation tests (BAT) using sera from allergic patients. In vivo cross-reactivity was examined using an IgE-mediated milk allergy mouse model.

Results

P34 was recognized by IgE antibodies from the sera of milk allergic patients, casein-specific monoclonal antibodies, and sera from milk-allergic mice. Spleen cells from sensitized mice incubated with milk, soy or P34 secreted IL-5 and IL-13, while IFN-γ remained unchanged. In addition, the cutaneous test was positive with cow's milk proteins (CMP) and P34 in the milk allergy mouse model. Moreover, milk-sensitized mice developed immediate symptoms following sublingual exposure to P34.

Conclusions

Our results demonstrate that P34 shares epitopes with bovine casein, which is responsible for inducing hypersensitivity symptoms in milk allergic mice. This is the first report of the in vivo cross-allergenicity of P34.

Expression of the soybean allergenic protein P34 in Escherichia coli and its indirect ELISA detection method

To detect the soybean allergen P34 (Gly m Bd 30K) from soybean products, the full-length cDNA sequence of P34 was synthesized and inserted into the prokaryotic expression vector pET-28a. The P34 protein was expressed in Escherichia coli BL21 (DE3) as an inclusion body under the induction of 0.8 mmol/L isopropyl β-D-1-thiogalactopyranoside. After purification with His-Bind affinity chromatography, the purity quotient of the recombinant protein was over 92 %, and its molecular weight (approximately 33 kDa) was very close to that of the native soybean P34. The polyclonal antibody (pAB) against P34 was prepared with the purified recombinant P34. The generated pAB, named as pAB-P34, exhibited high specificity to the P34 protein of the soybean meal. The indirect enzyme-linked immunosorbent assay (iELISA) based on pAB-P34 was established to determine the P34 content of soybean products. The CVs of the recovery tests of P34 were less than 7.77 %, which indicated that iELISA had high reproducibility and accuracy. Therefore, the recombinant P34 produced in the E. coli expression system, the prepared pAB-P34, and the developed iELISA could provide a valuable tool for sensitive detection of P34 in various soybean products and for future studies on allergies related to soybean P34.

Global gene expression profiles in developing soybean seeds

The gene expression profiles in soybean (Glycine max L.) seeds at 4 stages of development, namely, pod, 2-mm bean, 5-mm bean, and full-size bean, were examined by DNA microarray analysis. The total genes of each sample were classified into 4 clusters based on stage of development. Gene expression was strictly controlled by seed size, which coincides with the development stage. First, stage specific gene expression was examined. Many transcription factors were expressed in pod, 2-mm bean and 5-mm bean. In contrast, storage proteins were mainly expressed in full-size bean. Next, we extracted the genes that are differentially expressed genes (DEGs) that were extracted using the Rank products method of the Bioconductor software package. These DEGs were sorted into 8 groups using the hclust function according to gene expression patterns. Three of the groups across which the expression levels progressively increased included 100 genes, while 3 groups across which the levels decreased contained 47 genes. Storage proteins, seed-maturation proteins, some protease inhibitors, and the allergen Gly m Bd 28K were classified into the former groups. Lipoxygenase (LOX) family members were present in both the groups, indicating the multi-functionality with different expression patterns.

Milk and soy allergy

Cow's milk allergy (CMA) affects 2% to 3% of young children and presents with a wide range of IgE and non-IgE-mediated clinical syndromes, which have a significant economic and lifestyle effect. It is logical that a review of CMA would be linked to a review of soy allergy because soy formula is often an alternative source of nutrition for infants who do not tolerate cow's milk. This review examines the epidemiology, pathogenesis, clinical features, natural history, and diagnosis of cow's milk and soy allergy. Cross-reactivity and management of milk allergy are also discussed.

Soybean (Glycine max) allergy in Europe: Gly m 5 (beta-conglycinin) and Gly m 6 (glycinin) are potential diagnostic markers for severe allergic reactions to soy

BACKGROUND

Soybean is considered an important allergenic food, but published data on soybean allergens are controversial.

OBJECTIVE

We sought to identify relevant soybean allergens and correlate the IgE-binding pattern to clinical characteristics in European patients with confirmed soy allergy.

METHODS

IgE-reactive proteins were identified from a soybean cDNA expression library, purified from natural soybean source, or expressed in Escherichia coli. The IgE reactivity in 30 sera from subjects with a positive double-blind, placebo-controlled soybean challenge (n = 25) or a convincing history of anaphylaxis to soy (n = 5) was analyzed by ELISA or CAP-FEIA.

RESULTS

All subunits of Gly m 5 (beta-conglycinin) and Gly m 6 (glycinin) were IgE-reactive: 53% (16/30) of the study subjects had specific IgE to at least 1 major storage protein, 43% (13/30) to Gly m 5 , and 36% (11/30) to Gly m 6. Gly m 5 was IgE-reactive in 5 of 5 and Gly m 6 in 3 of 5 children. IgE-binding to Gly m 5 or Gly m 6 was found in 86% (6/7) subjects with anaphylaxis to soy and in 55% (6/11) of subjects with moderate but only 33% (4/12) of subjects with mild soy-related symptoms. The odds ratio (P < .05) for severe versus mild allergic reactions in subjects with specific IgE to Gly m 5 or Gly m6 was 12/1.

CONCLUSION

Sensitization to the soybean allergens Gly m 5 or Gly m 6 is potentially indicative for severe allergic reactions to soy.

Soybean beta-conglycinin as the main allergen in a patient with food-dependent exercise-induced anaphylaxis by tofu: food processing alters pepsin resistance

BACKGROUND

Food-dependent exercise-induced anaphylaxis (FDEIA) due to soybeans is a rare disorder. The allergen responsible for FDEIA due to soybeans has not yet been determined.

OBJECTIVE

We characterized the clinical features of a patient with FDEIA due to tofu, who was well tolerant to drinking soy milk. We then sought to identify the responsible soybean allergen(s) in that patient. We further studied whether different stabilities of the allergen(s) to pepsin digestion between two soybean products are related to their clinical allergenicity.

METHODS

Skin prick tests and provocation tests using soybean products were performed to detect the responsible food and other factors that induced the allergic symptoms. Specific IgE to various soybean allergens were examined by ImmunoCAP, ELISA and protein microarray assays. Immunoblotting for soybeans and soybean products using the patient's serum was also performed. Soybean products were serially digested by pepsin to disclose the stability of the allergens.

RESULTS

Provocation with ingestion of tofu and exercise induced the allergic symptoms, while ingestion of soy milk and exercise did not. Immunoblot analysis, ELISA and protein microarray assay revealed that beta-conglycinin mainly reacts with IgE antibodies in the patient's serum. By immunoblot analysis, beta-conglycinin in soy milk completely disappeared after pepsin digestion within 20 min, whereas beta-conglycinin in tofu was almost intact after more than 120 min of pepsin digestion.

CONCLUSION

We identified beta-conglycinin as the causative allergen in a patient with FDEIA induced by tofu. The difference in resistance to pepsin digestion between tofu and soy milk suggests that the presence of undigested allergens in the digestive tract is a prerequisite for the development of FDEIA.

BEID: database for sequence-structure-function information on antigen-antibody interactions

The B-cell Epitope Interaction Database (BEID; http://datam.i2r.a-star.edu.sg/BEID) is an open-access database describing sequence-structure-function information on immunoglobulin (Ig)-antigen interactions. The current version of the database contains 164 antigens, 126 Ig and 189 Ig-antigen complexes extracted from the Protein Data Bank (PDB). Each entry is manually verified, classified, and analyzed for intermolecular interactions between antigens and the corresponding bound Ig molecules. Ig-antigen interaction information that is stored in BEID includes solvent accessibility, hydrogen bonds, non-hydrogen bonds, gap volume, gap index, interface area and contact residues. The database can be searched with a user-friendly search tool and schematic diagrams for Ig-antigen interactions are available for download in PDF format. The ultimate purpose of BEID is to enhance the understanding of the rules of engagement between antigen and the corresponding bound Ig molecules. It is also a precious data source for developing computational predictors for B-cell epitopes.

Purification, thermal stability, and antigenicity of the immunodominant soybean allergen P34 in soy cultivars, ingredients, and products

Protein P34 (Gly m Bd 30K) is the immunodominant allergen in soybean (Glycine max L.). The objectives of this study were (1) to study the effect of thermal treatment on P34 antigenicity and secondary structure after isolation and purification of P34 from soybean by chromatographic techniques; (2) to identify the variability of P34 allergen within 138 accessions from a diverse USDA soybean germplasm collection by ELISA; and (3) to quantify P34 immunoreactivity in various commercial soy ingredients and products. Thermal processing decreased P34 antigenicity. Soybean accessions with the highest P34 content were ancestral (12 mg/g defatted flour) followed by modern (10 mg/g defatted flour) and exotic (8 mg/g defatted flour). The cultivar that emerged as the lowest-expressing P34 accession was PI548657 (2.3 mg/g defatted flour). Among commercial soy ingredients, soy flour yielded the highest P34 antigenicity (32 mg/g extracted protein) followed by soy protein isolate (29 mg/g extracted protein) and soy protein concentrate (24 mg/g extracted protein). Among soy consumer products, soymilk presented the highest P34 antigenicity, ranging from 7 to 23 mg/g extracted protein, followed by tempeh (8 mg/g extracted protein), soy infant formula (3.4 mg/g extracted protein), soy powder (2 mg/g extracted protein), and soy cheese products (0.50 mg/g extracted protein). Korean miso, soy sauce, soy chili mix, soy nuts, soy cream cheese, soy meat patty, texturized soy protein, and soy cereal exhibited undetectable P34 antigenicity (detection limit = 0.45 ng). Selecting soybean varieties with low levels of this allergen, or via processing, could potentially make soybean products less antigenic.

Soy allergy in perspective

PURPOSE OF REVIEW

The purpose of this paper is to review and discuss studies on soy allergy.

RECENT FINDINGS

In Central Europe soy is a clinically relevant birch pollen-related allergenic food. Crossreaction is mediated by a Bet v 1 homologous protein, Gly m 4. Additionally, birch pollen allergic patients might acquire through Bet v 1 sensitization allergies to mungbean or peanut, in which Vig r 1 and Ara h 8 are the main cross-reactive allergens. Threshold doses in soy allergic individuals range from 10 mg to 50 g of soy and are more than one order of magnitude higher than in peanut allergy. No evidence was found for increased allergenicity of genetically modified soybeans.

SUMMARY

In Europe, both primary and pollen-related food allergy exist. The diagnosis of legume allergy in birch pollen-sensitized patients should not be excluded on a negative IgE testing to legume extracts. Bet v 1 related allergens are often underrepresented in extracts. Gly m 4 from soy and Ara h 8 from peanut are nowadays commercially available and are recommended in birch pollen allergic patients with suspicion of soy or peanut allergy, but negative extract-based diagnostic tests to screen for IgE specific to these recombinant allergens.

Allergenicity of soybean: new developments in identification of allergenic proteins, cross-reactivities and hypoallergenization technologies

Soybean is considered one of the "big eight" foods that are believed to be responsible for 90% of all allergenic reactions. Soy allergy is of particular importance, because soybeans are widely used in processed foods and, therefore, represent a particularly insidious source of hidden allergens. Although significant advances have been made in the identification and characterization of soybean allergens, scientists are not completely certain about which proteins in soy cause allergic reactions. At least 16 allergens have been identified. Most of them, as with other plant food allergens, have a metabolic, storage, or protective function. These allergens belong to protein families which have conserved structural features in relation with their biological activity, which explains the wide immunochemical cross-recognition observed among members of the legume family. Detailed analysis of the structure-allergenicity relationships has been hampered by the complexity and heterogeneity of soybean proteins. A variety of technological approaches have been attempted to decrease soybean allergenicity. This paper provides a comprehensive review of the current body of knowledge on the identification and characterization of soybean allergens, as well as an update on current hypoallergenization techniques.

Allergen sequence databases

A number of specialized databases have been developed to facilitate studies of human allergens. These include molecular databases focused on protein sequences and structures, informational databases focused on clinical, biochemical and epidemiological data related to protein allergens, a database on allergen nomenclature, and other knowledge bases or informational websites that are peripherally-related to research on allergens. Examples of each type of databases are listed and described briefly in this review. Database construction and maintenance and their impact on database quality and usefulness are also discussed.

Evaluation of available IgE-binding epitope data and its utility in bioinformatics

This paper reviews the role played by IgE-binding epitopes in eliciting clinical symptoms, the types of IgE-binding epitopes in allergenic proteins, the methods used to identify IgE-binding epitopes, and the availability of IgE-binding epitopes in allergenic sources. Finally, bioinformatics methods to assess protein allergenicity using knowledge of IgE-binding epitopes are discussed.

Reduced Allergenic Potency of VR9-1, a Mutant of the Major Shrimp Allergen Pen a 1 (Tropomyosin)

The major shrimp allergen, tropomyosin, is an excellent model allergen for studying the influence of mutations within the primary structure on the allergenic potency of an allergen; Pen a 1 allows systematic evaluation and comparison of Ab-binding epitopes, because amino acid sequences of both allergenic and nonallergenic tropomyosins are known. Individually recognized IgE Ab-binding epitopes, amino acid positions, and substitutions critical for IgE Ab binding were identified by combinatorial substitution analysis, and 12 positions deemed critical were mutated in the eight major epitopes. The mutant VR9-1 was characterized with regard to allergenic potency by mediator release assays using sera from shrimp-allergic subjects and sera from BALB/c, C57BL/6J, C3H/HeJ, and CBA/J mice sensitized with shrimp extract using alum, cholera toxin, and Bordetella pertussis, as adjuvants. The secondary structure of VR9-1 was not altered; however, the allergenic potency was reduced by 90-98% measuring allergen-specific mediator release from humanized rat basophilic leukemia (RBL) cells, RBL 30/25. Reduced mediator release of RBL-2H3 cells sensitized with sera from mice that were immunized with shrimp extract indicated that mice produced IgE Abs to Pen a 1 and to the same epitopes as humans did. In conclusion, data obtained by mapping sequential epitopes were used to generate a Pen a 1 mutant with significantly reduced allergenic potency. Epitopes that are relevant for human IgE Ab binding are also major binding sites for murine IgE Abs. These results indicate that the murine model might be used to optimize the Pen a 1 mutant for future therapeutic use.

Risks of allergic reactions to biotech proteins in foods: perception and reality

In recent years, significant attention has been paid to the use of biotechnology to improve the quality and quantity of the food supply due in part to the projected growth in the world population, plus limited options available for increasing the amount of land under cultivation. Alterations in the food supply induced by classical breeding and selection methods typically involve the movement of large portions of genomic DNA between different plant varieties to obtain the desired trait. This is in contrast to techniques of genetic engineering which allows the selection and transfers specific genes from one species to another. The primary allergy risk to consumers from genetically modified crops may be placed into one of three categories. The first represents the highest risk to the allergic consumer is the transfer of known allergen or cross-reacting allergen into a food crop. The second category, representing an intermediate risk to the consumer, is the potential for replacing the endogenous allergenicity of a genetically-modified crop. The last category involves expression of novel proteins that may become allergens in man and generally represents a relatively low risk to the consumer, although this possibility has received attention of late. In order to mitigate the three categories of potential allergy risk associated with biotech crops, all genes introduced into food crops undergo a series of tests designed to determine if the biotech protein exhibits properties of known food allergens. The result of this risk assessment process to date is that no biotech proteins in foods have been documented to cause allergic reactions. These results indicate that the current assessment process is robust, although as science of allergy and allergens evolves, new information and new technology should help further the assessment process for potential allergenicity.

Structural, biological, and evolutionary relationships of plant food allergens sensitizing via the gastrointestinal tract

The recently completed genome sequence of the model plant species Arabidopsis has been estimated to encode over 25,000 proteins, which, on the basis of their function, can be classified into structural and metabolic (the vast majority of plant proteins), protective proteins, which defend a plant against invasion by pathogens or feeding by pests, and storage proteins, which proved a nutrient store to support germination in seeds. It is now clear that almost all plant food allergens are either protective or storage proteins. It is also becoming evident that those proteins that trigger the development of an allergic response through the gastrointestinal tract belong primarily to two large protein superfamilies: (1) The cereal prolamin superfamily, comprising three major groups of plant food allergens, the 2S albumins, lipid transfer proteins, and cereal alpha-amylase/trypsin inhibitors, which have related structures, and are stable to thermal processing and proteolysis. They include major allergens from Brazil nut, peanuts, fruits, such as peaches, and cereals, such as rice and wheat; (2) The cupin superfamily, comprising the major globulin storage proteins from a number of plant species. The globulins have been found to be allergens in plant foods, such as peanuts, soya bean, and walnut; (3) The cyteine protease C1 family, comprising the papain-like proteases from microbes, plants, and animals. This family contains two notable allergens that sensitize via the GI tract, namely actinidin from kiwi fruit and the soybean allergen, Gly m Bd 30k/P34. This study describes the properties, structures, and evolutionary relationships of these protein families, the allergens that belong to them, and discusses them in relation to the role protein structure may play in determining protein allergenicity.

Allergenic Proteins in Soybean: Processing and Reduction of P34 Allergenicity

Soybean ranks among the "big 8" of the most allergenic foods, and with increasing consumption of soybean products, the incidence of soy-caused allergies is expected to escalate. Soybean and its derivatives have become ubiquitous in vegetarian and many meat-based food products, and as a result, dietary avoidance has become difficult. However, soybeans can be manipulated in a variety of ways to alter their allergenicity. Several studies have focused on reducing the allergenicity of soybeans by changing the structure of the immunodominant allergen P34 using food processing, agronomic, or genetic manipulation techniques. A review of the literature pertaining to these studies is presented here.

Construction of hevein (Hev b 6.02) with reduced allergenicity for immunotherapy of latex allergy by comutation of six amino acid residues on the conformational IgE epitopes

Recently we have established that IgE Abs bind to conformational epitopes in the N- and C-terminal regions of the major natural rubber latex allergen, hevein (Hev b 6.02). To identify the critical amino acid residues that interact with IgE, the hevein sequence was scanned by using site-specific mutations. Twenty-nine hevein mutants were designed and produced by a baculovirus expression system in insect cells and tested by IgE inhibition-ELISA using sera from 26 latex allergic patients. Six potential IgE-interacting residues of hevein (Arg(5), Lys(10), Glu(29), Tyr(30), His(35), and Gln(38)) were identified and characterized further in detail. Based on these six residues, two triple mutants (Hdelta3A, Hdelta3B) and hevein mutant where all six residues were mutated (Hdelta6), were designed, modeled, and produced. Structural and functional properties of these combinatory mutants were compared experimentally and in silico with those of recombinant hevein. The IgE-binding affinity of the mutants decreased by three to five orders of magnitude as compared with that of recombinant hevein. Skin prick test reactivity of the triple mutant HDelta3A was drastically reduced and that of the six-residue mutant Hdelta6 was completely abolished in all patients examined in this study. The approach presented in this paper offers tools for identification and modification of amino acid residues on conformational epitopes of allergens that interact with IgE. Hevein with a highly reduced ability to bind IgE should provide a valuable candidate molecule for immunotherapy of latex allergy and is anticipated to have a low risk of systemic side effects.

Methods for allergen analysis in food: a review

Food allergies represent an important health problem in industrialized countries. Undeclared allergens as contaminants in food products pose a major risk for sensitized persons. A proposal to amend the European Food Labelling Directive requires that all ingredients intentionally added to food products will have to be included on the label. Reliable detection and quantification methods for food allergens are necessary to ensure compliance with food labelling and to improve consumer protection. Methods available so far are based on protein or DNA detection. This review presents an up-to-date picture of the characteristics of the major food allergens and collects published methods for the determination of food allergens or the presence of potentially allergenic constituents in food products. A summary of the current availability of commercial allergen detection kits is given. One part of the paper describes various methods that have been generally employed in the detection of allergens in food; their advantages and drawbacks are discussed in brief. The main part of this review, however, focuses on specific food allergens and appropriate methods for their detection in food products. Special emphasis is given to allergenic foods explicitly mentioned in the Amendment to the European Food Labelling Directive that pose a potential risk for allergic individuals, namely celery, cereals containing gluten (including wheat, rye and barley) crustaceans, eggs, fish, peanuts, soybeans, milk and dairy products, mustard, tree-nuts, sesame seeds, and sulphite at concentrations of at least 10 mg kg(-1). Sulphites, however, are not discussed.

Computational tools for the study of allergens

Allergy is a major cause of morbidity worldwide. The number of characterized allergens and related information is increasing rapidly creating demands for advanced information storage, retrieval and analysis. Bioinformatics provides useful tools for analysing allergens and these are complementary to traditional laboratory techniques for the study of allergens. Specific applications include structural analysis of allergens, identification of B- and T-cell epitopes, assessment of allergenicity and cross-reactivity, and genome analysis. In this paper, the most important bioinformatic tools and methods with relevance to the study of allergy have been reviewed.

Genetic modification removes an immunodominant allergen from soybean

The increasing use of soybean (Glycine max) products in processed foods poses a potential threat to soybean-sensitive food-allergic individuals. In vitro assays on soybean seed proteins with sera from soybean-sensitive individuals have immunoglobulin E reactivity to abundant storage proteins and a few less-abundant seed proteins. One of these low abundance proteins, Gly m Bd 30 K, also referred to as P34, is in fact a major (i.e. immunodominant) soybean allergen. Although a member of the papain protease superfamily, Gly m Bd 30 K has a glycine in the conserved catalytic cysteine position found in all other cysteine proteases. Transgene-induced gene silencing was used to prevent the accumulation of Gly m Bd 30 K protein in soybean seeds. The Gly m Bd 30 K-silenced plants and their seeds lacked any compositional, developmental, structural, or ultrastructural phenotypic differences when compared with control plants. Proteomic analysis of extracts from transgenic seed detected the suppression of Gly m Bd 30 K-related peptides but no other significant changes in polypeptide pattern. The lack of a collateral alteration of any other seed protein in the Gly m Bd 30 K-silenced seeds supports the presumption that the protein does not have a role in seed protein processing and maturation. These data provide evidence for substantial equivalence of composition of transgenic and non-transgenic seed eliminating one of the dominant allergens of soybean seeds.

Par j 1 and Par j 2, the major allergens from Parietaria judaica pollen, have similar immunoglobulin E epitopes

BACKGROUND

Parietaria judaica is the main cause of allergy in Mediterranean countries. The major allergens from P. judaica pollen, Par j 1 and Par j 2, have amino acid sequence identity of 45% and contain eight cysteine residues involved in disulphide bonds that compact the structure.

OBJECTIVE

The aim of the study was to identify IgE-binding epitopes on Par j 1 and Par j 2, the major allergens from P. judaica pollen and correlate them with the three-dimensional structure of the proteins.

METHODS

Overlapping peptides representing the complete length of Par j 1 and Par j 2 were synthesized on a cellulose-derivatized membrane. Sera from 17 P. judaica-allergenic patients were used to identify IgE-binding epitopes. Homology modelling of the three dimensional structure of both allergens was generated using the Swiss-Model software on the basis of previously reported crystal structures.

RESULTS

Five and eight IgE-binding epitopes were identified on Par j 1 and Par j 2 allergens, respectively. Both proteins belonged to the non-specific lipid transfer proteins (ns-LTP) family and therefore a three-dimensional model of both allergens was constructed on the basis of the maize ns-LTP crystal structure. Par j 1 and Par j 2 allergens have three similar allergenic epitopes with high homology and identical conformation.

CONCLUSION

Three similar IgE-epitopes of major allergens from P. judaica have been described. They could be good candidates for designing of IgE haptens as therapeutic agents with reduced anaphylactic side-effects or for developing hypoallergenic variants of these major allergens.

Ana o 1, a cashew (Anacardium occidental) allergen of the vicilin seed storage protein family

BACKGROUND

The allergens responsible for cashew food allergy have not been well characterized.

OBJECTIVES

We initiated a study to clone cDNAs encoding cashew food allergens.

METHODS

A cashew cDNA library was screened with human serum for IgE-reactive clones and rabbit IgG anti-cashew extract antisera. Reactive clones were sequenced and expressed, and linear epitopes were identified by means of solid-phase overlapping peptide analysis. Immunoblot inhibition was used to identify the native peptide in cashew extract.

RESULTS

Four closely related clones reactive with both human and rabbit antisera were sequenced. Sequence analysis showed that these encode members of the vicilin/sucrose-binding protein family of plant seed storage proteins. Screening of the recombinant protein with sera from 20 patients with cashew allergy and 8 cashew-tolerant patients with allergies to other tree nuts showed that 50% and 25% of sera from patients with cashew allergy and cashew-tolerant subjects, respectively, bound the recombinant protein. The corresponding native allergen protein, designated Ana o 1, was located at approximately 50 kd. Epitope mapping revealed 11 linear IgE-binding epitopes, of which 3 appear to be immunodominant. None of the epitopes were shared in common with those of the peanut vicilin allergen Ara h 1.

CONCLUSION

Ana o 1, a vicilin-like protein, is a major food allergen in cashews. Cashew and peanut vicilins do not share linear epitopes.

Linear IgE epitope mapping of the English walnut (Juglans regia) major food allergen, Jug r 1

BACKGROUND

Peanut and tree nut allergies can be life-threatening, and they appear to be growing in prevalence. Jug r 1, a 2S albumin seed storage protein, was previously characterized as a major English walnut food allergen.

OBJECTIVE

We sought to identify the linear IgE-binding epitopes of Jug r 1 and to determine which, if any, amino acids are necessary for this binding to occur.

METHODS

Pools of sera from walnut-allergic patients and overlapping peptides synthesized on an activated cellulose membrane were used to screen for IgE-binding epitopes. Mutational analysis of the immunodominant epitope was carried out through single and multisite amino acid substitutions. Inhibition assays were performed through use of affinity-purified IgE, soluble forms of the epitope peptide, and the recombinant 2S albumin, rJug r 1.

RESULTS

One immunodominant linear epitope was identified. Amino acid mutations to the epitope demonstrated that the residues RGEE, at positions 36 through 39, were minimally required for IgE binding. Probing of this epitope with sera from each of 20 patients revealed 15 of the sera to be positive. Binding of patients' IgE to the epitope was inhibited with a soluble form of the peptide; however, soluble peptide did not completely inhibit the binding of IgE to the intact rJug r 1.

CONCLUSION

One major linear IgE-reactive epitope and its critical core amino acid residues have been identified. Mutation of any of these core amino acids resulted in loss of IgE binding to the epitope, and this points toward the feasibility of reducing allergenicity in genetically modified walnuts. However, strong evidence for the existence of conformational epitopes was also obtained.

How to make foods safer--genetically modified foods

It is the responsibility of companies developing genetically modified foods, and of regulatory authorities that approve their marketing, to ensure that they are at least as safe as the traditional foods they are intended to replace in the diet. This requires that any novel material introduced into the food material should not be allergenic. If the novel gene has come from an allergenic source, e.g. nuts, it is necessary to demonstrate using immunological procedures applied to the IgE fractions of pooled sera from individuals with confirmed allergies that the novel protein is non-allergenic. When the novel gene is from a non-allergenic source then it is necessary to demonstrate lack of significant amino acid sequence homology to known allergens together with sensitivity to food manufacturing and digestive processes. Consumer confidence in genetically modified foods would be significantly improved if hypoallergenic varieties of crops and food products that are currently allergenic could be developed. Techniques such as antisense technology and single site amino acid substitution have been shown to have such potential.