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

Structure of allergens and structure based epitope predictions

The structure determination of major allergens is a prerequisite for analyzing surface exposed areas of the allergen and for mapping conformational epitopes. These may be determined by experimental methods including crystallographic and NMR-based approaches or predicted by computational methods. In this review we summarize the existing structural information on allergens and their classification in protein fold families. The currently available allergen-antibody complexes are described and the experimentally obtained epitopes compared. Furthermore we discuss established methods for linear and conformational epitope mapping, putting special emphasis on a recently developed approach, which uses the structural similarity of proteins in combination with the experimental cross-reactivity data for epitope prediction.

Expression of flavonoid 3',5'-hydroxylase and acetolactate synthase genes in transgenic carnation: assessing the safety of a nonfood plant

For 16 years, genetically modified flowers of carnation ( Dianthus caryophyllus ) have been sold to the floristry industry. The transgenic carnation carries a herbicide tolerance gene (a mutant gene encoding acetolactate synthase (ALS)) and has been modified to produce delphinidin-based anthocyanins in flowers, which conventionally bred carnation cannot produce. The modified flower color has been achieved by introduction of a gene encoding flavonoid 3',5'-hydroxylase (F3'5'H). Transgenic carnation flowers are produced in South America and are primarily distributed to North America, Europe, and Japan. Although a nonfood crop, the release of the genetically modified carnation varieties required an environmental risk impact assessment and an assessment of the potential for any increased risk of harm to human or animal health compared to conventionally bred carnation. The results of the health safety assessment and the experimental studies that accompanied them are described in this review. The conclusion from the assessments has been that the release of genetically modified carnation varieties which express F3'5'H and ALS genes and which accumulate delphinidin-based anthocyanins do not pose an increased risk of harm to human or animal health.

Toxicological evaluation of proteins introduced into food crops

This manuscript focuses on the toxicological evaluation of proteins introduced into GM crops to impart desired traits. In many cases, introduced proteins can be shown to have a history of safe use. Where modifications have been made to proteins, experience has shown that it is highly unlikely that modification of amino acid sequences can make a non-toxic protein toxic. Moreover, if the modified protein still retains its biological function, and this function is found in related proteins that have a history of safe use (HOSU) in food, and the exposure level is similar to functionally related proteins, then the modified protein could also be considered to be "as-safe-as" those that have a HOSU. Within nature, there can be considerable evolutionary changes in the amino acid sequence of proteins within the same family, yet these proteins share the same biological function. In general, food crops such as maize, soy, rice, canola etc. are subjected to a variety of processing conditions to generate different food products. Processing conditions such as cooking, modification of pH conditions, and mechanical shearing can often denature proteins in these crops resulting in a loss of functional activity. These same processing conditions can also markedly lower human dietary exposure to (functionally active) proteins. Safety testing of an introduced protein could be indicated if its biological function was not adequately characterized and/or it was shown to be structurally/functionally related to proteins that are known to be toxic to mammals.

Food proteins from different allergen families sensitize Balb/c mice to family-specific immune responses

The classification of food allergens based on the structure and function of proteins contributes to the study of the relationship between bioinformatics and potential allergenicity of allergens. Food allergens always share sequence similarity with the allergens in the same allergen families. For that reason, food proteins from different allergen families may induce different patterns of immune responses in animal models. Female Balb/c mice (3-4-weeks-old) were sensitized with food proteins once per week for 4 weeks, and then challenged 2 weeks later (on Day 42 of study). Blood was collected (to obtain serum levels of histamine and protein-specific IgG1 and IgE antibodies) and measures of vascular permeability were performed 20 min after the challenge. Five food proteins (11S globulin, OVA [ovalbumin], HAS [human serum albumin] and LRP [lysine-responsive storage protein] of different allergen families, and Cry 1Ab/Ac [crystal protein]) were used to assess patterns of immune responses for each allergen family and then bioinformatics and digestive stability in simulated gastric fluid were employed to assess the overall utility of the Balb/c. The assay results indicated that, in this model, histamine and protein-specific IgE antibody levels and vascular permeability could be used to identify allergenicity of 11S globulin, OVA, and PAP (potato acid phosphatase) only. However, the results of the protein-specific IgG1 measures could only distinguish allergic food proteins with negative control. Based on bioinformatic analyses, the five different food proteins clearly induced distinct patterns of immune responses in the Balb/c model.

The sensitising capacity of intact β-lactoglobulin is reduced by co-administration with digested β-lactoglobulin

BACKGROUND

It is generally believed that protein hydrolysis in the gastrointestinal tract decreases the allergenicity of food allergens. However, it remains unknown if specific properties of digestion products determine whether a sensitisation or tolerogenic immune response will develop. We sought to examine the sensitising capacity of the cow's milk allergen β-lactoglobulin (BLG) and digestion products thereof in a Brown Norway (BN) rat model.

METHODS

Intact BLG was digested in an in vitro model simulating the gastro-duodenal digestion process and subsequently fractionated by gel permeation chromatography. BN rats were dosed with either PBS, 200 µg of intact BLG, 30 µg of intact BLG, 200 µg of partially digested BLG, 200 µg of digested BLG, or with 200 µg of a fraction of large complexes or a fraction of small complexes. Sera from BN rats were analysed for specific antibodies and avidity was measured.

RESULTS

BLG partly resisted the digestion process. However, the BLG molecules that did not survive the digestion process were rapidly broken down to peptides of sizes less than Mr 4,500. Specific antibody responses revealed that both 200 and 30 µg of intact BLG had immunogenic as well as sensitising capacity, while digested BLG could not induce any specific antibodies. Most importantly, while intact BLG showed a significant sensitising capacity when administered alone, this sensitising capacity was significantly reduced when co-administered with digested BLG.

CONCLUSIONS

Co-immunisation of intact BLG with digested BLG reduces the sensitising capacity of intact BLG, which could result from tolerogenic mechanisms induced by the digestion products.

Innate immunostimulatory properties of allergens and their relevance to food allergy

Food allergy is an increasingly prevalent disease of immune dysregulation directed to a small subset of proteins. Shared structural and functional features of allergens, such as glycosylation, lipid-binding and protease activity may provide insight into the mechanisms involved in the induction of primary Th2 immune responses. We review the literature of innate Th2-type immune activation as a context for better understanding the properties of allergens that contribute to the induction of Th2-biased immune responses in at least a subset of individuals. Th2-priming signals have been largely identified in the context of parasite immunity and wound healing. Some of the features of parasite antigens and the innate immune responses to them are now understood to play a role in allergic inflammation as well. These include both exogenous and endogenous activators of innate immunity and subsequent release of key cytokine mediators such as thymic stromal lymphopoietin (TSLP), interleukin (IL)-25 and IL-33. Moreover, numerous innate immune cells including epithelium, dendritic cells, basophils, innate lymphoid cells and others all interact to shape the adaptive Th2 immune response. Progress toward understanding Th2-inducing innate immune signals more completely may lead to novel strategies for primary prevention and therapy of respiratory and food allergies.

Mass spectrometry in the proteome analysis of mature cereal kernels

In the last decade, the improved performance and versatility of the mass spectrometers together with the increasing availability of gene and genomic sequence database, led the mass spectrometry to become an indispensable tool for either protein and proteome analyses in cereals. Mass spectrometric works on prolamins have rapidly evolved from the determination of the molecular masses of proteins to the proteomic approaches aimed to a large-scale protein identification and study of functional and regulatory aspects of proteins. Mass spectrometry coupled with electrophoresis, chromatographic methods, and bioinformatics tools is currently making significant contributions to a better knowledge of the composition and structure of the cereal proteins and their structure-function relationships. Results obtained using mass spectrometry, including characterization of prolamins, investigation of the gluten toxicity for coeliac patients, identification of proteins responsible of cereal allergies, determination of the protein pattern and its modification under environmental or stress effects, investigation of genetically modified varieties by proteomic approaches, are summarized here, to illustrate current trends, analytical troubles and challenges, and suggest possible future perspectives.

Determinants of food allergy

Food allergy is an emerging epidemic in the United States and the Western world. The determination of factors that make certain foods allergenic is still not clearly understood. Only a tiny fraction of thousands of proteins and other molecules is responsible for inducing food allergy. In this review, the authors present 3 examples of food allergies with disparate clinical presentations: peanut, soy, and mammalian meat. The potential relationships between allergen structure and function, emphasizing the importance of cross-reactive determinants, immunoglobulin E antibodies to the oligosaccharides, and the immune responses induced in humans are discussed.

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.

Mobilization of seed protein reserves

The mobilization of seed storage proteins upon seed imbibition and germination is a crucial process in the establishment of the seedling. Storage proteins fold compactly, presenting only a few vulnerable regions for initial proteolytic digestion. Evolutionarily related storage proteins have similar three-dimensional structure, and thus tend to be initially cleaved at similar sites. The initial cleavage makes possible subsequent rapid and extensive breakdown catalyzed by endo- and exopeptidases. The proteolytic enzymes that degrade the storage proteins during mobilization identified so far are mostly cysteine proteases, but also include serine, aspartic and metalloproteases. Plants often ensure early initiation of storage protein mobilization by depositing active proteases during seed maturation, in the very compartments where storage proteins are sequestered. Various means are used in such cases to prevent proteolytic attack until after imbibition of the seed with water. This constraint, however, is not always enforced as the dry seeds of some plant species contain proteolytic intermediates as a result of limited proteolysis of some storage proteins. Besides addressing fundamental questions in plant protein metabolism, studies of the mobilization of storage proteins will point out proteolytic events to avoid in large-scale production of cloned products in seeds. Conversely, proteolytic enzymes may be applied toward reduction of food allergens, many of which are seed storage proteins.

Digested Ara h 1 loses sensitizing capacity when separated into fractions

The major peanut allergen Ara h 1 is an easily digestible protein under physiological conditions. The present study revealed that pepsin digestion products of Ara h 1 retained the sensitizing potential in a Brown Norway rat model, while this sensitizing capacity was lost by separating the digest into fractions by gel permeation chromatography. Protein chemical analysis showed that the peptide composition as well as the aggregation profiles of the fractions of Ara h 1 digest differed from that of the whole pool. These results indicate that the sensitizing capacity of digested Ara h 1 is a consequence of the peptides being in an aggregated state resembling the intact molecule or that most peptides of the digests need to be present in the same solution, having a synergistic or adjuvant effect and thereby augmenting the immune response against other peptides.

Molecular diagnosis of peanut and legume allergy

PURPOSE OF REVIEW

To review and discuss recent studies on molecular diagnosis of peanut and other legume allergy.

RECENT FINDINGS

Studies from the UK and France suggest that quantification of Ara h 2-specific IgE may accurately discriminate peanut allergy from tolerance. However, the pattern of allergenic component recognition in peanut-sensitized patients from different populations or geographical areas varies, reflecting different pollen and dietary exposures. In the USA, peanut-allergic patients are commonly sensitized to Ara h 1-3, in Spain to Ara h 9 and in Sweden to Ara h 8. Patients with soybean allergy sensitized to Gly m 5 or Gly m 6 allergens may be at greater risk of experiencing severe allergic reactions.

SUMMARY

Accurate diagnosis of peanut and legume allergy is challenging and essential. Measurement of IgE response to specific allergenic molecules may be more useful in predicting the presence and severity of clinical allergy than currently used skin or blood tests based on whole extracts. However, given the heterogeneity in component recognition patterns observed in different geographical areas, further studies are essential to identify and confirm potentially useful molecular diagnostic and prognostic markers. Until such markers are confirmed and replicated in different age groups, oral food challenge (OFC) remains the gold standard for accurate diagnosis.

Effect of roasting on the allergenicity of major peanut allergens Ara h 1 and Ara h 2/6: the necessity of degranulation assays

BACKGROUND

Peanuts are often consumed after roasting, a process that alters the three-dimensional structure of allergens and leads to Maillard modification. Such changes are likely to affect their allergenicity.

OBJECTIVE

We aimed to establish the effect of thermal treatment mimicking the roasting process on the allergenicity of Ara h 1 and a mix of 2S albumins from peanut (Ara h 2/6).

METHODS

Ara h 1 and Ara h 2/6 were purified from raw peanuts and heated in a dry form for 20 min at 145°C in the presence (R+g) or absence (R-g) of glucose, and soluble proteins were then extracted. Sera obtained from 12 well-characterized peanut-allergic patients were used to assess the IgE binding and degranulation capacities of the allergens.

RESULTS

Extensive heating at low moisture resulted in the hydrolysis of both Ara h 1 and Ara h 2/6. However, in contrast to Ara h 2/6, soluble R+g Ara h 1 formed large aggregates. Although the IgE-binding capacity of R+g and R-g Ara h 1 was decreased 9000- and 3.6-fold, respectively, compared with native Ara h 1, their capacity to elicit mediator release was increased. Conversely, both the IgE-binding capacity and the degranulation capacity of R-g Ara h 2/6 were 600-700-fold lower compared with the native form, although the presence of glucose during heating significantly moderated these losses.

CONCLUSIONS AND CLINICAL RELEVANCE

Extensive heating reduced the degranulation capacity of Ara h 2/6 but significantly increased the degranulation capacity of Ara h 1. This observation can have important ramifications for component-resolved approaches for diagnosis and demonstrates the importance of investigating the degranulation capacity in addition to IgE reactivity when assessing the effects of food processing on the allergenicity of proteins.

Sensitization with 7S globulins from peanut, hazelnut, soy or pea induces IgE with different biological activities which are modified by soy tolerance

BACKGROUND

It is not known why some foods sensitizing via the gastrointestinal tract are prevalent allergenic foods and others are not. Eating habits, processing, and the food matrix have been suggested to influence the allergenicity of a given food. Factors related to protein structure, such as stability to digestion, have also been suggested. 7S globulins from peanut, hazelnut, soy, and pea were studied to determine whether related proteins would induce a similar sensitization when removed from their 'normal' matrix.

METHODS

Brown Norway rats (soy tolerant or nontolerant) were immunized i.p. 3 times with 100 μg purified peanut, hazelnut, soy, or pea 7S without adjuvant. Sera were analyzed for specific antibodies by different ELISAs (IgG1, IgG2a, and IgE), inhibition ELISA, and rat basophilic leukemia cell assay.

RESULTS

The 4 related 7S globulins induced a response with an almost identical level of specific antibodies, but peanut 7S induced IgE of higher avidity than hazelnut and pea 7S which, again, had a higher avidity than IgE induced by soy 7S. Soy tolerance reduced the functionality of IgE without influencing antibody titers.

CONCLUSIONS

Although the 4 7S globulins are structurally related allergens, they induce antibodies with different antigen-binding characteristics. Peanut 7S induces IgE of a higher avidity than hazelnut and pea 7S which, again, has a higher avidity than IgE induced by soy 7S. We also show that soy tolerance influences the function of antibodies to peanut 7S. These findings may help explain how antibodies of different clinical significances can develop in different individuals sensitized to the same allergen.

Changes in protein expression profiles between a low phytic acid rice ( Oryza sativa L. Ssp. japonica) line and its parental line: a proteomic and bioinformatic approach

The seed proteome of a low phytic acid (lpa) rice line (Os-lpa-XS110-1), developed as a novel food source, was compared to that of its parental line, Xiushui 110 (XS-110). Analysis by surfaced enhanced laser desorption ionization-time-of-flight mass spectrometry (SELDI-TOF MS) and two-dimensional gel electrophoresis (2-DE) allowed the detection of a potential low molecular weight biomarker and identification of 23 differentially expressed proteins that include stress-related proteins, storage proteins, and potential allergens. Bioinformatic analyses revealed that triose phosphate isomerase (TPI) and fructose bisphosphatealdolase (FBA), two major differentially expressed proteins, are involved in myo-inositol metabolism. Accumulation of globulin was also significantly decreased in the lpa line. This study demonstrates the potential of proteomic and bioinformatic profiling techniques for safety assessment of novel foods. Furthermore, these techniques provide powerful tools for studying functional genomics due to the possibility of identifying genes related to the mutated traits.

The structural characteristics of nonspecific lipid transfer proteins explain their resistance to gastroduodenal proteolysis

The structure and stability of the allergenic nonspecific lipid transfer protein (LTP) of peach were compared with the homologous LTP1 of barley and its liganded form LTP1b. All three proteins were resistant to gastric pepsinolysis and were only slowly digested at 1 to 2 out of 14 potential tryptic and chymotryptic cleavage sites under duodenal conditions. Peach LTP was initially cleaved at Tyr79-Lys80 and then at Arg39-Thr40 (a site lost in barley LTP1). Molecular dynamics simulations of the proteins under folded conditions showed that the backbone flexibility is limited, explaining the resistance to duodenal proteolysis. Arg39 and Lys80 side chains were more flexible in simulations of peach compared with barley LTP1. This may explain differences in the rates of cleavage observed experimentally for the two proteins and suggests that the flexibility of individual amino acid side chains could be important in determining preferred proteolytic cleavage sites. In order to understand resistance to pepsinolysis, proteins were characterized by NMR spectroscopy at pH 1.8. This showed that the helical regions of both proteins remain folded at this pH. NMR hydrogen exchange studies confirmed the rigidity of the structures at acidic pH, with barley LTP1 showing some regions with greater protection. Collectively, these data suggest that the rigidity of the LTP scaffold is responsible for their resistance to proteolysis. Gastroduodenal digestion conditions do not disrupt the 3D structure of peach LTP, explaining why LTPs retain their ability to bind IgE after digestion and hence their allergenic potential.

In vitro digestion of Cry1Ab proteins and analysis of the impact on their immunoreactivity

A pepsin resistance test performed at pH 1.2 and with high pepsin to protein ratio is one of the steps of the weight-of-evidence approach used for assessment of allergenicity of new proteins. However, the use of other in vitro digestibility tests, performed in more physiologically relevant conditions and in combination with immunological assays so as to increase the value of the information gained from the studies of stability of a novel protein to digestion for the overall allergenicity assessment, has been proposed. This study then aimed to investigate the stability to digestion of Cry1Ab protoxin and toxin, insecticidal proteins expressed in genetically modified crops, using simulated gastric fluid (SGF) at different pH values and pepsin-to-substrate ratios, in the presence or absence of physiological surfactant phosphatidylcholine (PC). Electrophoresis and immunoblot patterns and residual immunoreactivity of digesta were analyzed. Although Cry1Ab protoxin is extensively degraded at pH 1.2 with high pepsin-to-protein ratio, it is only slightly degraded at pH 2.0 and conserved its immunoreactivity. Furthermore, Cry1Ab proteins were demonstrated to be stable in a more physiologically relevant in vitro digestibility test (pH 2.5, pepsin-to-substrate ratio 1:20 (w/w) with PC). Factors such as pH, SGF composition, and pepsin-to-substrate ratio then greatly influence the digestion of Cry1Ab proteins, confirming that new and more physiologically relevant in vitro digestibility tests should be also considered to study the relationship between the resistance of a protein to digestion and its allergenicity.

Structural stability of Amandin, a major allergen from almond (Prunus dulcis), and its acidic and basic polypeptides

Information relating to the resistance of food allergens to thermal and/or chemical denaturation is critical if a reduction in protein allergenicity is to be achieved through food-processing means. This study examined the changes in the secondary structure of an almond allergen, amandin, and its acidic and basic polypeptides as a result of thermal and chemical denaturation. Amandin ( approximately 370 kDa) was purified by cryoprecipitation followed by gel filtration chromatography and subjected to thermal (13-96 degrees C) and chemical (urea and dithiothreitol) treatments. Changes in the secondary structure of the protein were followed using circular dichroism spectroscopy. The secondary structure of the hexameric amandin did not undergo remarkable changes at temperatures up to 90 degrees C, although protein aggregation was observed. In the presence of a reducing agent, irreversible denaturation occurred with the following experimental values: T(m) = 72.53 degrees C (transition temperature), DeltaH = 87.40 kcal/mol (unfolding enthalpy), and C(p) = 2.48 kcal/(mol degrees C) (heat capacity). The concentration of urea needed to achieve 50% denaturation was 2.59 M, and the Gibbs free energy of chemical denaturation was calculated to be DeltaG = 3.82 kcal/mol. The basic and acidic polypeptides of amandin had lower thermal stabilities than the multimeric protein.

Evidence for novel tomato seed allergens: IgE-reactive legumin and vicilin proteins identified by multidimensional protein fractionation-mass spectrometry and in silico epitope modeling

Tomato fruit and seed allergens were detected by IgE-immunoblotting using sera from 18 adult tomato-sensitized patients selected based on a positive history skin prick test (SPT) and specific Immunglobulin (Ig) E-levels. Isolated tomato seed total protein showed high SPT activity comparable or even higher than tomato fruit protein. For the molecular characterization of tomato seed allergens, a multidimensional protein fractionation strategy and LC-MS/MS was used. Two legumin- and vicilin-proteins were purified and showed strong IgE-reactivity in immunoblots. Individual patient sera exhibited varying IgE-sensitivity against the purified proteins. In silico structural modeling indicates high homology between epitopes of known walnut allergens and the detected IgE-crossreactive tomato proteins.

Resolution and identification of major peanut allergens using a combination of fluorescence two-dimensional differential gel electrophoresis, Western blotting and Q-TOF mass spectrometry

Peanut allergy is triggered by several proteins known as allergens. In this study, the complexity the peanut allergome is investigated with proteomic tools. The strength of this investigation resides in combining the high-resolving power and reproducibility of fluorescence two-dimensional differential gel electrophoresis with specific immunological detection as well as polypeptide sequencing by high-resolution mass spectrometry. Matching of the peanut proteins in 2D gels was achieved by differential labelling whereby peanut proteins and purified allergens (Ara h 1, Ara h 2 or Ara h 3/4) were run on the same gel. Ten protein spots on a mass line of ca. 63-68 kDa were likely to correspond to Ara h 1. Two doublets on two different mass lines at ca. 16 and 18 kDa matched with purified allergen Ara h 2. The basic and acidic sub-units of Ara h 3/4 were observed at masses of ca. 25 kDa and 40-45 kDa, respectively. Subsequently the antibody-binding capacity of spots corresponding to peanut allergens was investigated by Western blotting of 2D gels using antibodies (IgY) raised against Ara h 1, Ara h 2 and the recombinant 40 kDa sub-unit of Ara h 3/4. Final confirmation of the identity of the protein spots matched after 2D electrophoresis and identified by Western blotting was obtained by in-gel digestion of protein spots and analysis by quadrupole time-of-flight mass spectrometry. By using the method developed in our work, the location and identification of two different isoforms of the allergen Ara h 1, the allergen Ara h 2 and six isoforms of the allergen Ara h 3/4 in 2D peanut protein maps was established.

Purification and structural stability of the peach allergens Pru p 1 and Pru p 3

Pru p 1 (a Bet v 1 homologue) and Pru p 3 (a nonspecific lipid transfer protein; nsLTP) are major allergenic proteins in peach fruit, but differ in their abundance and stability. Pru p 1 has low abundance and is highly labile and was purified after expression as a recombinant protein in Escherichia coli. Pru p 3 is highly abundant in peach peel and was purified by conventional methods. The identities of the proteins were confirmed by sequence analysis and their masses determined by MS analysis. The purified proteins reacted with antisera against related allergens from other species: Pru p 1 with antiserum to Bet v 1 and Pru p 3 with antiserum to Mal d 3 (from apple). The presence of secondary and tertiary structure was demonstrated by circular dichroism (CD) and high field NMR spectroscopy. CD spectroscopy also showed that the two proteins differed in their stability at pH 3 and in their ability to refold after heating to 95 degrees C. Thus, Pru p 1 was unfolded at pH 3 even at 25 degrees C but was able to refold after heating to 95 degrees C at pH 7.5. In contrast, Pru p 3 was unable to refold after heating under neutral conditions but readily refolded after heating at pH 3.

Comparative proteomical analysis of zygotic embryo and endosperm from Coffea arabica seeds

During coffee seed development, proteins are predominantly deposited in cotyledons and in the endosperm. Reserve proteins of the 11S family are the most abundant globulins in coffee seeds, acting as a nitrogen source during roasting and guaranteeing flavor and aroma. The aim of the present study was to compare the protein profiles of endosperm and zygotic embryos of coffee seeds. Proteins were extracted from whole seed as well as from embryo and endosperm, separately. Total proteins were analyzed by two-dimensional electrophoresis (2-DE) followed by identification by mass spectrometry (MS). The most abundant spots observed in the gels of coffee seeds were excised, digested with trypsin, and identified by MS as subunits of the 11S globulin. Spots with identical pI and molecular masses were also observed in the protein profiles of coffee endosperm and embryo, indicating that 11S protein is also highly expressed in those tissues. Peptide sequence coverage of about 20% of the entire 11S globulin was obtained. Three other proteins were identified in the embryo and endosperm 2-DE profiles as a Cupin superfamily protein, an allergenic protein (Pru ar 1), exclusive to the endosperm 2D map, and a hypothetical protein, observed only in the zygotic embryo profile.

IgE antibodies to omega-5 gliadin associate with immediate symptoms on oral wheat challenge in Japanese children

BACKGROUND

Gliadins have been implicated in immunoglobulin E (IgE)-mediated allergy to ingested wheat and omega-5-gliadin is known to represent a major allergen in wheat-dependent exercise-induced anaphylaxis. Less known is whether omega-5-gliadin is a clinically relevant allergen in children with immediate allergy to ingested wheat. This study investigates whether specific IgE antibodies to omega-5-gliadin (sIgE-omega-5-gliadin-ab) could be used as a marker for oral wheat challenge outcome in wheat-sensitized children. A secondary objective was to study whether the level of sIgE-omega-5-gliadin was related to symptom severity in children with a positive challenge test.

METHODS

Serum samples from 88 children sensitized to wheat, of whom 35 underwent wheat challenge, were collected consecutively. sIgE-omega-5-gliadin-ab was related to a physician's diagnosis of wheat allergy and challenge symptoms.

RESULTS

The mean concentration of sIgE-omega-5-gliadin-ab was 7.25 kU(A)/l in patients with wheat allergy and 1.08 kU(A)/l in patients with no wheat allergy (P < 0.01). sIgE-omega-5-gliadin-ab was only detected in 12 of the non-wheat allergic children and 11 of them had a specific IgE to wheat below 1.30 kU(A)/l. Children reacting with severe symptoms upon challenge (n = 8) had increased levels of sIgE-omega-5-gliadin-ab compared to children with moderate, mild or no symptoms (P < 0.001).

CONCLUSIONS

The presence of sIgE-omega-5-gliadin-ab is related to the reaction level to wheat challenge outcome in wheat-sensitized children. The sIgE-omega-5-gliadin-ab was found to be associated with a strong convincing history of wheat allergy also in those cases when oral food challenge was avoided. The sIgE-omega-5-gliadin-ab level may serve as a marker for clinical reactivity in wheat-sensitized individuals.