The effect of the food matrix on in vivo immune responses to purified peanut allergens

There is little knowledge about the factors that determine the allergenicity of food proteins. One aspect that remains to be elucidated is the effect of the food matrix on immune responses to food proteins. To study the intrinsic immunogenicity of allergens and the influence of the food matrix, purified peanut allergens (Ara h 1, Ara h 2, Ara h 3, or Ara h 6) and a whole peanut extract (PE) were tested in the popliteal lymph node assay (PLNA) and in an oral model of peanut hypersensitivity. In the PLNA, peanut proteins were injected into the hind footpad of BALB/c mice; in the oral exposure experiments C3H/HeOuJ mice were gavaged weekly with PE or allergens in the presence of cholera toxin (CT). Upon footpad injection, none of the allergens induced significant immune activation. In contrast, PE induced an increase in cell number, cytokine production, and activation of antigen-presenting cells. Furthermore, the presence of a food matrix enhanced the immune response to the individual allergens. Oral exposure to the purified allergens in the presence of CT induced specific IgE responses, irrespective of the presence of a food matrix. These results suggest that purified peanut allergens possess little intrinsic immune-stimulating capacity in contrast to a whole PE. Moreover, the data indicate that the food matrix can influence responses to individual proteins and, therefore, the food matrix must be taken into account when developing models for allergenic potential assessment.

Large scale purification of rapeseed proteins (Brassica napus L.)

Rapeseed (Brassica napus L.) cruciferin (12S globulin), napin (2S albumin) and lipid transfer proteins (LTP) were purified at a multi-g scale. The procedure developed was simple, rather fast and resolutive; it permitted the recovery of these proteins with a good yield, such as 40% for cruciferin and 18% for napin. Nanofiltration eliminated the major phenolic compounds. The remaining protein fraction was fractionated by cation exchange chromatography (CEC) on a streamline SP-XL column in alkaline conditions. The unbound neutral cruciferin was polished by size exclusion chromatography. The alkaline napin isoforms and LTP, adsorbed on the beads, were eluted as a whole fraction and further separated by an other CEC step at acidic pH. Napins were polished by hydrophobic interaction chromatography (HIC). The fractions were characterized by reverse phase HPLC, electrophoresis, N-terminal sequencing and mass spectrometry. All the fractions contained less than 5% of impurities.

Influence of the maillard reaction on the allergenicity of rAra h 2, a recombinant major allergen from peanut (Arachis hypogaea), its major epitopes, and peanut agglutinin

The influence of thermal processing and nonenzymatic browning reactions on the IgE-binding activity of rAra h 2 was studied and compared to findings recently reported for the allergen's natural counterpart. ELISA experiments as well as inhibition assays revealed that thermal treatment of rAra h 2 in the presence of reactive carbohydrates and carbohydrate breakdown products induces a strong increase of the IgE-binding activity, thus collaborating with the data reported for the natural protein isolated from peanuts. To localize the Ara h 2 sequences responsible for the formation of highly IgE-affine glycation sites, model peptides have been synthesized mimicking sequences which contain possible targets for glycation as well as the immunodominant epitopes. Immunological evaluation of these peptides heated in the absence or presence of reducing sugars and carbonyls, respectively, revealed that neither the two lysine residues of Ara h 2 nor its N-terminus are involved in the formation of IgE-affine structures by Maillard reaction. Also, the cysteine-containing major epitope 3 (aa 27-36) was found to lose its IgE-binding capacity upon heating. By contrast, the overlapping major epitopes 6 and 7, which do not contain any lysine or arginine moieties, showed a distinct higher level of IgE binding when subjected to Maillard reaction, thus giving the first evidence that nonbasic amino acids might be accessible for nonenzymatic glycation reactions and that these posttranslational modifications might induce increased IgE binding of the glycated Ara h 2. Analogous experiments were performed with peanut agglutinin, considered in the literature as a minor allergen. ELISA experiments revealed that the majority of tested sera samples from peanut-sensitive patients showed a high level of IgE binding to the lectin even after heat treatment. In contradiction to published data, nonenzymatic browning reactions seem to deteriorate the IgE affinity of the lectin.

Emulsion properties of sunflower (Helianthus annuus) proteins

Emulsions were made with sunflower protein isolate (SI), helianthinin, and sunflower albumins (SFAs). Emulsion formation and stabilization were studied as a function of pH and ionic strength and after heat treatment of the proteins. The emulsions were characterized with respect to average droplet size, surface excess, and the occurrence of coalescence and/or droplet aggregation. Sunflower proteins were shown to form stable emulsions, with the exception of SFAs at neutral and alkaline pH values. Droplet aggregation occurred in emulsions made with SI, helianthinin, and SFAs. Droplet aggregation and subsequent coalescence of emulsions made with SFAs could be prevented at pH 3. Calcium was found to cause droplet aggregation of emulsions made with helianthinin, at neutral and alkaline pH values. Treatments that increase conformational flexibility of the protein molecule improved the emulsion properties of sunflower proteins.

Isolation and characterization of natural Ara h 6: evidence for a further peanut allergen with putative clinical relevance based on resistance to pepsin digestion and heat

Peanut allergy is a significant health problem because of its prevalence and the potential severity of the allergic reaction. The characterization of peanut allergens is crucial to the understanding of the mechanism of peanut allergy. Recently, we described cloning of the peanut allergen Ara h 6. The aim of this study was isolation and further characterization of nAra h 6. We purified nAra h 6 from crude peanut extract using gel filtration and anion exchange chromatography. The preparation was further characterized by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) with subsequent immunoblotting. Stability of nAra h 6 was studied by an in vitro digestibility assay as well as by resistance against thermal processing. Sequencing of nAra h 6 identified the N-terminal amino acid sequence as MRRERGRQGDSSS. Further results clearly demonstrated stability of nAra h 6 against pepsin digestion and heating. Immunoglobulin G (IgE) binding analysis and its biological activity shown by RBL 25/30-test of natural Ara h 6 supported the importance of this peanut allergen. Investigation of nAra h 6 revealed evidence for a further peanut allergen with putative clinical relevance based on resistance to pepsin digestion and heat.

Stability of the major allergen Brazil nut 2S albumin (Ber e 1) to physiologically relevant in vitro gastrointestinal digestion

The major 2S albumin allergen from Brazil nuts, Ber e 1, was subjected to gastrointestinal digestion using a physiologically relevant in vitro model system either before or after heating (100 degrees C for 20 min). Whilst the albumin was cleaved into peptides, these were held together in a much larger structure even when digested by using a simulated phase 1 (gastric) followed by a phase 2 (duodenal) digestion system. Neither prior heating of Ber e 1 nor the presence of the physiological surfactant phosphatidylcholine affected the pattern of proteolysis. After 2 h of gastric digestion, approximately 25% of the allergen remained intact, approximately 50% corresponded to a large fragment of M(r) 6400, and the remainder comprised smaller peptides. During duodenal digestion, residual intact 2S albumin disappeared quickly, but a modified form of the 'large fragment' remained, even after 2 h of digestion, with a mass of approximately 5000 Da. The 'large fragment' comprised several smaller peptides that were identified, by using different MS techniques, as deriving from the large subunit. In particular, sequences corresponding to the hypervariable region (Q37-M47) and to another peptide (P42-P69), spanning the main immunoglobulin E epitope region of 2S albumin allergens, were found to be largely intact following phase 1 (gastric) digestion. They also contained previously identified putative T-cell epitopes. These findings indicate that the characteristic conserved skeleton of cysteine residues of 2S albumin family and, particularly, the intrachain disulphide bond pattern of the large subunit, play a critical role in holding the core protein structure together even after extensive proteolysis, and the resulting structures still contain potentially active B- and T-cell epitopes.

Extensive in vitro cross-reactivity to seed storage proteins is present among walnut (Juglans) cultivars and species

BACKGROUND

Tree nuts, including English walnuts (Juglans regia), are sources of food allergens often associated with life-threatening allergic reactions. It is unknown if seed storage proteins from other Juglans species have IgE epitopes similar to those of the important English walnut allergens, Jug r 1 (2S albumin) and Jug r 2 (vicilin-like).

OBJECTIVE

To screen for potential germplasm sources of hypoallergenic seed storage proteins of relevance in walnut food allergy. We sought to identify English walnut cultivars (cvs) or other Juglans species that showed decreased IgE binding to major seed storage proteins or an inability to cross-react with Jug r 1 or Jug r 2.

METHODS

We determined if IgE in sera of patients who have had life-threatening systemic reactions to English walnut bound protein extracts from all tested walnut cvs (57 cvs total) or species (six) by Western immunoblot. Further, we used immunoblot inhibition to determine the in vitro cross-reactivity of Jug r 1 and Jug r 2, native and recombinant, with several walnut species.

RESULTS

All walnut cvs and species contain allergenic proteins. Furthermore, as shown by in vitro immunoblot inhibition, the major walnut allergens in the species tested cross-reacted with those in J. regia cv. Chandler and J. nigra cv. Thomas extracts.

CONCLUSIONS

Based on our findings, it is unlikely that a composite hypoallergenic walnut could be bred from available germplasm. In addition, patients with severe allergy to English walnut are likely to be clinically allergic to all commercial English walnut cvs and other closely related Juglans species.

Solution structure and stability against digestion of rproBnIb, a recombinant 2S albumin from rapeseed: relationship to its allergenic properties

NMR spectroscopy has been used to determine the solution structure of the precursor form of the recombinant napin BnIb, rproBnIb, a 2S albumin, 109-residue protein from the seeds of Brassica napus. More than 90% of the side-chain proton resonances were unambiguously assigned from the analysis of two-dimensional correlation (COSY), total correlation (TOCSY), and nuclear Overhauser effect (NOESY) spectra. The final structures were computed by using restrained molecular dynamics on the basis of 1316 upper-limit distance constraints derived from NOE cross-correlation intensities. The computed structures exhibited a root-mean-square deviation (RMSD) radius of 0.66 A for the backbone and 1.16 A for the side-chain heavy atoms of the structural core. The resulting structure consists of five amphipathic helices arranged in a right-handed super helix, a folding motif found in other proteins of the prolamin superfamily. As in the case of the mature protein, the recombinant precursor behaves as a plant food allergen. To trace out the origin and characteristics of its allergenic properties, rproBnIb was assayed against simulated gastric fluid and found to be very resistant to proteolysis. Also, heat treatment of the protein followed up to 85 degrees C by circular dichroism showed a very limited unfolding, which was recovered after cooling to 20 degrees C, indicating a high thermal stability. These results suggest that rproBnIb, as other 2S albumins, may be able to reach the gut immune system intact. A comparison of the putative epitopes against IgE antibodies of the three members of the prolamine family [2S albumins, nonspecific lipid transfer proteins (nsLTPs), and alpha-amylase/trypsin inhibitors] indicates that there are not common surfaces of interaction with IgE. Though the epitopes appear to be located in different regions of the proteins, they do comply with the requirements of being solvent-exposed and flexible.

Reversible denaturation of Brazil nut 2S albumin (Ber e1) and implication of structural destabilization on digestion by pepsin

The high resistance of Brazil nut 2S albumin, previously identified as an allergen, against proteolysis by pepsin was examined in this work. Although the denaturation temperature of this protein exceeds the 110 degrees C at neutral pH, at low pH a fully reversible thermal denaturation was observed at approximately 82 degrees C. The poor digestibility of the protein by pepsin illustrates the tight globular packing. Chemical processing (i.e., subsequent reduction and alkylation of the protein) was used to destabilize the globular fold. Far-UV circular dichroism and infrared spectroscopy showed that the reduced and alkylated form had lost its beta-structures, whereas the alpha-helix content was conserved. The free energy of stabilization of the globular fold of the processed protein as assessed by a guanidine titration study was only 30-40% of that of the native form. Size exclusion chromatography indicated that the heavy chain lost its globular character once separated from the native 2S albumin. The consequences of these changes in structural stability for degradation by pepsin were analyzed using gel electrophoresis and mass spectrometry. Whereas native 2S albumin was digested slowly in 1 h, the reduced and alkylated protein was digested completely within 30 s. These results are discussed in view of the potential allergenicity of Brazil nut 2S albumin.

Characterization of the T-cell epitopes of a major peanut allergen, Ara h 2

BACKGROUND

The development of safe and effective immunotherapy for peanut allergy has been complicated by the high anaphylactic potential of native peanut extracts. We sought to map the T-cell epitopes of the major peanut allergen, Ara h 2 in order to develop T-cell targeted vaccines.

METHODS

A panel of eight peanut-specific CD4+ T-cell lines (TCL) was derived from eight peanut-allergic subjects and proliferative and cytokine responses to stimulation with a set of overlapping 20-mer peptides representing the entire sequence of Ara h 2 determined. Proliferation was assessed in 72 h assays via tritiated thymidine incorporation, while interleukin (IL)-5 and interferon (IFN)-gamma production were assessed via sandwich enzyme-linked immunosorbent assay (ELISA) of cell culture supernatants.

RESULTS

Eight of the 17 Ara h 2 peptides were recognized by one or more subjects, with the two peptides showing highest reactivity [Ara h 2 (19-38) and Ara h 2 (73-92)] being recognized by three subjects each. Adjoining peptides Ara h 2 (28-47) and Ara h 2 (100-119) induced proliferative responses in two subjects. Each of these peptides was associated with a Th2-type cytokine response.

CONCLUSION

Two highly immunogenic T-cell reactive regions of Ara h 2 have been identified, Ara h 2 (19-47) and Ara h 2 (73-119), providing scope for the development of safe forms of immunotherapy for peanut allergy.

The major human structural IgE epitope of the Brazil nut allergen Ber e 1: a chimaeric and protein microarray approach

A protein microarray system containing different dilutions of 77 related and non-related proteins was used to show that IgE from subjects allergic to Brazil nut specifically recognise the seed 2S albumin protein (Ber e 1). Further, correctly folded chimaeric 2S albumin proteins containing structural epitope replacement were constructed and directed to the secretion pathway of the methylotropic yeast Pichia pastoris. Through the use of a chimaeric protein microarray system together with sera from a panel of 18 well-characterised Brazil nut allergic subjects, a structural IgE epitope of Ber e 1 was mapped to a helix-loop-helix region. The same structural region has been previously reported as the immunodominant region in related food allergens by different techniques. In conclusion, the combination of chimaeric proteins and protein microarrays will greatly facilitate the screening of a large number of individuals for a particular structural epitope and help to further our understanding of how proteins are recognised by the adaptive immune system.

Conformational states of sunflower (Helianthus annuus) Helianthinin: effect of heat and pH

The structure and solubility of helianthinin, the most abundant protein of sunflower seeds, was investigated as a function of pH and temperature. Dissociation of the 11S form (hexamer) into the 7S form (trimer) gradually increased with increasing pH from 5.8 to 9.0. High ionic strength (I = 250 mM) stabilizes the 11S form at pH > 7.0. Heating and low pH resulted in dissociation into the monomeric constituents (2-3S). Next, the 7S and 11S forms of helianthinin were isolated and shown to differ in their secondary and tertiary structure, and to have denaturation temperatures (T(d)) of 65 and 90 degrees C, respectively. Furthermore, the existence of two populations of the monomeric form of helianthinin with denaturation temperatures of 65 and 90 degrees C was described. This leads to the hypothesis that helianthinin can adopt two different conformational states: one with T(d) = 65 degrees C and a second with T(d) = 90 degrees C.

Competitive inhibition ELISA for quantification of Ara h 1 and Ara h 2, the major allergens of peanuts

Allergies to peanuts are becoming an increasingly important health problem as a result of the persistence and severity of the reaction in allergic individuals. Because no treatment currently is available, avoidance is the only option for peanut-allergic individuals. Avoidance of an abundant and often disguised food such as peanuts, however, is very difficult; therefore, competitive inhibition ELISAs were developed to detect and quantitate each of the major peanut allergens, Ara h 1 and Ara h 2. Under optimal conditions for each assay, the sensitivity of the Ara h 1 and Ara h 2 detection assays were 12 and 0.5 ng/mL, respectively. These assays were primarily devised to effectively compare the levels of Ara h 1 and Ara h 2 in a wide variety of peanuts or peanut products but can also be used to identify cross-reactive antigens. The method is simple and rapid, requiring only one allergen-specific antibody and, therefore, could be adapted specifically to detect the presence of these individual allergens in different foods.

Can commercial peanut assay kits detect peanut allergens?

Peanut is the food group mostly associated with severe and fatal allergic reactions. In the United States, more than 90% of peanut-allergic individuals' serum IgE recognized peanut proteins Ara h 1 and Ara h 2, thus establishing these proteins as major peanut allergens. The amount of Ara h 1 and Ara h 2 in 3 varieties of peanut cultivars that are commonly processed in the industrialized countries was determined to be 12-16 and 6-9%, respectively. Current commercial peanut test kits use polyclonal peanut-specific antibodies to detect soluble or buffer extractable peanut proteins. Because the 2 major peanut allergens Ara h 1 and Ara h 2 are isolated from soluble peanut proteins, it is generally assumed that these commercial kits can detect peanut allergens, although none of these kits claims to detect peanut allergen. This study showed for the first time that the peanut test kits could, in fact, detect major peanut allergens Ara h 1 and Ara h 2 in both native or heat-denatured structures; therefore, these kits qualified to be classified as peanut allergen enzyme-linked immunosorbent assays.

Development of an epitope-specific analytical tool for the major peanut allergen Ara h 2 using a high-density multiple-antigenic peptide strategy

Using the major peanut allergen Ara h 2 as an example, an analytical tool enabling the determination of immunoglobulin E (IgE)-epitopes in processed food allergens was developed. We synthesized a multiple-antigenic peptide (MAP) of the IgE-reactive linear epitope 3 (amino acid positions 27-36) of Ara h 2 and raised a monospecific antiserum against this epitope to obtain a positive control for future epitope resolved diagnostics. First, a MAP of epitope 3, having a molecular mass of 7770 Da, was synthesized, purified, and its structure confirmed by liquid chromatography-mass spectrometry (electrospray ionization) (LC-MS(ESI)), matrix assisted laser desorption/ionization-time of flight (MALDI-TOF), and Edman sequencing. The MAP was then used to raise high titer antibodies in rabbits using the adjuvant Titermax and to characterize the specificity of IgE from allergenic patients sensitized to Ara h 2. The antiserum exclusively detects Ara h 2 in crude peanut extract with a titer of 10(7) by Western blot and reacts specifically with epitope 3 shown by epitope mapping for a library of solid-phase-bound synthetic 15-mer peptides covering the entire sequence of Ara h 2. Such IgE-reactive epitopes are of high analytical relevance as they could constitute the basis for epitope-specific detection systems for use in quality control in the food industry or for forensic purposes in cases of fatal reactions to otherwise undetected peanut proteins.

A napin-like polypeptide with translation-inhibitory, trypsin-inhibitory, antiproliferative and antibacterial activities from kale seeds

A heterodimeric napin-like polypeptide with translation-inhibiting and antibacterial activities has been isolated from kale seeds. The purification procedure entailed ion-exchange chromatography on dielthylaminoethyl (DEAE)-cellulose, affinity chromatography on Affi-gel blue gel, ion-exchange chromatography by fast protein liquid chromatography (FPLC) on Mono S, and gel filtration by FPLC on Superdex 75. The napin-like polypeptide was unadsorbed on DEAE-cellulose but adsorbed on Affi-gel blue gel and Mono S. Its 7-kDa large subunit differs in N-terminal amino acid sequence from the 4-kDa small subunit. The polypeptide inhibited translation in the rabbit reticulocyte lysate system with an IC50 of 37.5 nM. This activity was preserved between pH 5 and pH 11, and between 10 and 40 degrees C. It fell to a low level at pH 3 and pH 13 and at 70 degrees C. Antibacterial activity against Bacillus, Megabacterium, and Pseudomonas species and antiproliferative activity against leukemia L1210 cells were observed. However, the polypeptide did not exert antifungal, ribonuclease, or protease activity.

Isoforms of the Major Peanut Allergen Ara h 2: IgE Binding in Children with Peanut Allergy

BACKGROUND

The major peanut allergen Ara h 2 consists of two isoforms, namely Ara h 2.0101 and Ara h 2.0201. The recently identified Ara h 2.0201 isoform contains an extra 12 amino acids including an extra copy of the reported immunodominant epitope DPYSPS. This study aimed to evaluate the IgE binding of the two Ara h 2 isoforms.

METHODS

Ten clones of Ara h 2 were sequenced to assess the relative frequency of the Ara h 2 isoforms and to identify whether there was further variation in the Ara h 2 sequence. IgE binding to Ara h 2.0101 and Ara h 2.0201 was measured for 70 peanut-allergic children using an IgE DELFIA assay to quantitate specific IgE binding. A competition assay was used to measure whether Ara h 2.0201 contained IgE epitopes other than those found for Ara h 2.0101.

RESULTS

The original Ara h 2.0101 sequence was found for 6/10 clones and Ara h 2.0201 was found for 2/10 clones. Ara h 2.0201 had the expected insertion of 12 amino acids as well as substitutions at positions 40 (40G) and 142 (142E). Two new isoforms were identified as different polymorphisms of position 142. One Ara h 2.01 clone (Ara h 2.0102) contained 142E and one Ara h 2.02 clone (Ara h 2.0202) contained 142D. A polymorphism that was previously identified by other investigators at position 77 (77Q or 77R) was not found for any of the 10 sequences. Although the level of IgE binding to Ara h 2.0201 of individual patients was frequently higher than the binding to Ara h 2.0101 (p < 0.01), there was a strong correlation in binding to both isoforms (r = 0.987, p < 0.0001) and when analyzed as a group the means were similar. Ara h 2.0101 was not as efficient at blocking reactivity to Ara h 2.0201 indicating there is an additional IgE specificity for the Ara h 2.0201 isoform.

CONCLUSIONS

Ara h 2.0201 has similar but higher IgE binding than the originally sequenced Ara h 2.0101 isoform and contains other IgE specificities.

Effect of pH and ionic strength modifications on thermal denaturation of the 11S globulin of sunflower (Helianthus annuus)

Helianthinin, the main storage protein of sunflowers, has low water solubility and does not form a gel when heated; this behavior is different from other 11S globulins and limits its food applications. To understand this particular behavior, changes on helianthinin association-dissociation state induced by modifications in pH and ionic strength were analyzed. The influence of these different medium conditions on its thermal stability and tendency to form aggregates was also studied. Helianthinin behavior at different pH values and ionic strengths is similar to other 11S globulins except that it remains in a trimeric form at pH 11. Helianthinin thermal stability is higher than other 11S globulins but is lower than oat 11S globulin. Alkaline pH produces a 10 degrees C decrease of its denaturation temperature and also of the cooperativity of denaturation process, but it does not affect the denaturation activation energy. The decrease in thermal stability with the pH increase is also manifested by its tendency to form aggregates by SH/SS interchange reactions. When thermal treatments at alkaline pH are performed, all helianthinin subunits form aggregates, characterized by a higher proportion of beta-polypeptides than alpha-polypeptides, which is an indication that aggregation is accompanied by dissociation. Treatments at 80 degrees C are sufficient to induce aggregation but not to produce denaturation, and in these conditions hexameric forms remain after the treatment.

Detailed physicochemical characterization of the 2S storage protein from rape (Brassica napus L.)

Chromatographic, chemical, and spectroscopic techniques were used to characterize the physicochemical properties of napin purified by preparative chromatography. The molar extinction coefficient was determined (epsilon = 0.56), and static and dynamic light scattering measurements enabled the average molecular weight (M(w) = 13919), the second virial coefficient (A(2) = 23.95 x 10(-)(5) mol cm(3) g(-)(2)), and the hydrodynamic radius (R(H) = 1.98 nm) to be determined. No conformational changes were observed by fluorescence and circular dichroism measurements in different buffers at pH 3, 4.6, 7, and 12, confirming the high pH stability of this protein. From MALDI-TOF analysis and after enzymatic digestion, it was found that this purified sample, extracted from the rapeseed variety Express, contained mainly isoform 2SS3_BRANA.

[Polymorphism and inheritance of seed storage protein in sunflower]

The data on polymorphism and inheritance of the seed storage protein helianthinin are presented. The results of hybrid analysis indicate that in the annual sunflower Helianthus annuus, helianthinin synthesis is controlled by at least three loci: HelA, HelB, HelB, and HelC. Codominant alleles controlling different electrophoretic variants of polypeptides were identified at each of the loci. The HelA locus was inherited independently of HelB and HelC in a series of dihybrid crosses. The frequencies of recombination between loci HelB and HelC estimated in F2 and BC of two crossing combinations were respectively 21.8 and 19.0%. Segregation of the Hel-C-controlled variants in the progenies from the crosses of cultured sunflower with annual wild species and forms corresponded to that theoretically expected for Mendelian inheritance. The maternal type of helianthinin inheritance was observed in the progenies from the crosses of inbred H. annuus lines with perennial diploid and polyploid Helianthus species. Altered expression of the HelC locus was detected in some hybrid combinations. These alterations appeared in early (F1, F2) hybrid generations and were similar in different hybrid combinations. They did not depend on the perennial paternal species being more influenced by the maternal genotype and by the mode of obtaining hybrids (in an embryo culture or in the field). These results are explained by "genomic shock" generated by hybridization of genetically incompatible species.

Mixed antibody and T cell responses to peanut and the peanut allergens Ara h 1, Ara h 2, Ara h 3 and Ara h 6 in an oral sensitization model

BACKGROUND

Peanut allergy is known for its severity and persistence through life. Several peanut proteins have been identified as allergenic and are indicated as Ara h 1-7. Very little is known about the mechanisms that underlie sensitization to peanut proteins.

OBJECTIVE

The purpose of the present study was to reveal the immune responses that are induced against peanut and the peanut allergens Ara h 1, Ara h 2, Ara h 3 and Ara h 6 during sensitization, including the very early responses.

METHODS

Humoral and T cell responses against peanut and the peanut allergens were examined in an early and later stage of sensitization in an established murine model of peanut anaphylaxis. Therefore C3H/HeJ mice were orally exposed to two different doses of peanut extract plus cholera toxin.

RESULTS

Oral sensitization to peanut was characterized by an antigen-induced mixed cytokine response in the spleen (IL-4, IL-5, IL-10 and IFN-gamma), which could already be observed 7 days after the onset of exposure. Additionally, polyisotypic humoral responses (IgE, IgG1 and IgG2a) against peanut were found in the serum. Moreover, we demonstrated that these T helper (Th)1/Th2 cytokine and antibody responses were also directed specifically against the major peanut allergens Ara h 1, Ara h 2, Ara h 3 and Ara h 6.

CONCLUSIONS

This study implicates that both Th1 and Th2 phenomena are involved in the development of peanut allergy in the C3H/HeJ murine model. Furthermore, we show that the present oral model is suitable to examine immune responses to food allergens during different stages of sensitization upon treatment with a whole food extract.

Transport of ricin and 2S albumin precursors to the storage vacuoles of Ricinus communis endosperm involves the Golgi and VSR-like receptors

We have studied the transport of proricin and pro2S albumin to the protein storage vacuoles of developing castor bean (Ricinus communis L.) endosperm. Immunoelectron microscopy and cell fractionation reveal that both proteins travel through the Golgi apparatus and co-localize throughout their route to the storage vacuole. En route to the PSV, the proteins co-localize in large (>200 nm) vesicles, which are likely to represent developing storage vacuoles. We further show that the sequence-specific vacuolar sorting signals of both proricin and pro2SA bind in vitro to proteins that have high sequence similarity to members of the VSR/AtELP/BP-80 vacuolar sorting receptor family, generally associated with clathrin-mediated traffic to the lytic vacuole. The implications of these findings in relation to the current model for protein sorting to storage vacuoles are discussed.

Solution structure of a methionine-rich 2S albumin from sunflower seeds: relationship to its allergenic and emulsifying properties

The three-dimensional structure in aqueous solution of SFA-8, a 2S albumin 103-residue protein from seeds of sunflower (Helianthus anuus L.), has been determined by NMR methods. An almost complete (1)H resonance assignment was accomplished from analysis of two-dimensional (2D) COSY and 2D TOCSY spectra, and the structure was computed by using restrained molecular dynamics on the basis of 1393 upper limit distance constraints derived from NOE cross-correlation intensities measured in 2D NOESY spectra. In contrast with most other 2S albumins, SFA-8 consists of a single polypeptide chain without any cleavage in the segment of residues 30-46. The computed structures exhibited an rmsd radius of 0.52 A for the backbone structural core (residues 11-30 and 46-101) and 1.01 A for the side chain heavy atoms. The resulting structure consists of five amphipathic helices arranged in a right-handed superhelix, a folding motif first observed in nonspecific lipid transfer (nsLTP) proteins, and common to other 2S albumins. In contrast to nsLTP proteins, neither SFA-8 nor RicC3 (a 2S albumin from castor bean) has an internal cavity that is able to host a lipid molecule, which results from an exchange in the pairing of disulfide bridges in the CXC segment. Both 2S albumins and nonspecific lipid transfer proteins belong to the prolamin superfamily, which includes a number of important food allergens. Differences in the extension and solvent exposition of the so-called "hypervariable loop" (which connects helices III and IV) in SFA-8 and RicC3 may be responsible for the different allergenic properties of the two proteins. SFA-8 has been shown to form highly stable emulsions with oil/water mixtures. We propose that these properties may be determined partly by a hydrophobic patch at the surface of the protein which consists of five methionines that partially hide the Trp76 residue. The flexibility of the loop which contains Trp76 and the hydrophobicity of the whole environment may favor a conformational change, by which the Trp76 side chain may become inserted into the oil phase.

Relevance of Ara h1, Ara h2 and Ara h3 in peanut-allergic patients, as determined by immunoglobulin E Western blotting, basophil-histamine release and intracutaneous testing: Ara h2 is the most important peanut allergen

BACKGROUND

A number of allergenic proteins in peanut has been described and the relative importance of these allergens is yet to be determined.

OBJECTIVES

We have investigated the relevance of previously identified peanut allergens in well-characterized peanut-allergic patients by in vitro, ex vivo and in vivo assays.

METHODS

Thirty-two adult peanut-allergic patients were included based on careful and standardized patient history and the presence of peanut-specific IgE. The diagnosis peanut allergy was confirmed using double-blind placebo-controlled food challenges in 23 patients. Major peanut allergens Ara h1, Ara h2 and Ara h3 were purified from peanuts using ion-exchange chromatography. IgE immunoblotting was performed and IgE-cross-linking capacity was examined by measuring histamine release (HR) after incubating patient basophils as well as passively sensitized basophils with several dilutions of the allergens. Intracutaneous tests (ICTs) using 10-fold dilution steps of the purified allergens and crude peanut extract were performed.

RESULTS

Ara h2 was recognized most frequently (26 out of 32) in all tests and induced both positive skin tests and basophil degranulation at low concentrations, whereas Ara h1 and Ara h3 were recognized less frequently and reacted only at 100-fold higher concentrations as analysed with HR and intracutaneous testing (ICT). Next to the three tested allergens, proteins with molecular weights of somewhat smaller than 15 kDa were identified as a IgE-binding proteins on immunoblot in the majority of the patients (20 out of 32).

CONCLUSION

We conclude that Ara h2 is, for our patient group, the most important peanut allergen, and that previously unidentified peanut proteins with molecular weights of somewhat smaller than 15 kDa may be important allergens as well. ICT in combination with basophil-HR and IgE immunoblotting provides insight in the patient specificity towards the individual peanut allergens.

High-yield expression in Escherichia coli, purification, and characterization of properly folded major peanut allergen Ara h 2

Allergic reactions to peanuts are a serious health problem because of their high prevalence, associated with potential severity, and chronicity. One of the three major allergens in peanut, Ara h 2, is a member of the conglutin family of seed storage proteins. Ara h 2 shows high sequence homology to proteins of the 2S albumin family. Presently, only very few structural data from allergenic proteins of this family exist. For a detailed understanding of the molecular mechanisms of food-induced allergies and for the development of therapeutic strategies knowledge of the high-resolution three-dimensional structure of allergenic proteins is essential. We report a method for the efficient large-scale preparation of properly folded Ara h 2 for structural studies and report CD-spectroscopic data. In contrast to other allergenic 2S albumins, Ara h 2 exists as a single continuous polypeptide chain in peanut seeds, and thus heterologous expression in Escherichia coli was possible. Ara h 2 was expressed as Trx-His-tag fusion protein in E. coli Origami (DE3), a modified E. coli strain with oxidizing cytoplasm which allows the formation of disulfide bridges. It could be shown that recombinant Ara h 2, thus overexpressed and purified, and the allergen isolated from peanuts are identical as judged from immunoblotting, analytical HPLC, and circular dichroism spectra.

Protein patterns of the Brassica rapa ovules and seeds under altered gravity

Electrophoretic investigation of protein patterns of Brassica rapa L. ovules and seeds from plants grown under clinorotation and in the laboratory control was carried out. Ovules at different stages (7 and 18 days after pollination) and mature seeds were analyzed. Polymorphism of seed storage proteins of B. rapa was taken into consideration in analysis of changes in ovule protein patterns under clinorotation. The appearance of a protein component in the region of about 43 kDa was detected in protein patterns of 7-day-old and 18-day-old ovules in the clinostat variants. Under altered gravity, in 18-day-old ovules, the appearance of a protein in the region of about 70 kDa was also revealed. The appearance of the protein component with the similar mobility (about 43 kDa) in ovules of different age from plants grown at clinorotation suggests that synthesis of this protein may be associated with the plant response to altered gravity. However, the investigation of the nature of this protein and its role requires further research to rule out its appearance because of genotypic differences between ovules of the control and experimental variants.

Mass spectrometry and structural characterization of 2S albumin isoforms from Brazil nuts (Bertholletia excelsa)

Proteomic approaches have been used to characterise the main 2S albumin isoforms from Brazil nuts (Bertholletia excelsa). Whilst most isoforms ( approximately 10 discrete protein species) exhibited molecular masses of around 12 kDa with a high amino acid sequence homology, important charge heterogeneity was found, with pIs varying between 4.6 and 6.6, with one >or=7.0. Proteomic analysis showed that these corresponded to a total of six National Center for Biotechnology Information (NCBI) accessions and that three isoforms had been purified to homogeneity corresponding to gi/384327, 112754 and 99609. The latter sequence corresponds to an isoform, previously only identified at the nucleotide sequence level, had a slightly higher molecular weight (13.4 kDa), and with noticeable differences in the primary structure. Proteins corresponding to six different NCBI accessions were identified, the heterogeneity of which had been increased by posttranslational processing. Evidence was found of cyclization of the N-terminal glutamine residue in two isoforms, together with ragged C-termini, indicative of carboxypeptidase activity within the vacuole following posttranslational processing. No evidence of glycosylation was found. Circular dichroism (CD) and Fourier transform-infrared (FT-IR) spectroscopy indicated all the studied isoforms were predominantly alpha-helical in nature, but that the Mr 13400 species was structurally distinct, with a higher proportion of alpha-helical structure.

Microarray immunoassay: association of clinical history, in vitro IgE function, and heterogeneity of allergenic peanut epitopes

BACKGROUND

IgE epitope mapping of food allergens is a prerequisite for engineering hypoallergenic immunotherapeutic agents and might reveal basic information regarding a patient's immune response. Mapping of large numbers of epitopes by using individual patient sera has been impractical with current techniques.

OBJECTIVE

We sought to develop a peptide microarray-based immunoassay to map peanut epitopes by using microliter quantities of serum.

METHODS

A set of 213 overlapping 20-residue peptides was synthesized corresponding to the primary sequences of Ara h 1, Ara h 2, and Ara h 3. These were arrayed in triplicate along with the corresponding recombinant proteins onto glass slides and used for immunolabeling.

RESULTS

Seventy-seven patient and 15 control sera were analyzed. The majority of patients (97%) had specific IgE to at least one of the recombinant allergens, and 87% had detectable IgE to sequential epitopes. Microarray mapping correlated well with previous studies. However, the analysis of individual patients revealed remarkable heterogeneity in the number and patterns of epitope recognition. High epitope diversity was found in patients with a history of more severe allergic reactions. Also, sensitization of effector cells with more diverse IgE antibodies conferred greater reactivity to specific allergen.

CONCLUSIONS

The protein microarray immunoassay confirmed that Ara h 1, Ara h 2, and Ara h 3 are major peanut allergens and allows for parallel epitope analysis. This has led to the discovery of an additional important epitope of Ara h 1 and the recognition of a high degree of patient heterogeneity. This qualitative difference in epitope diversity might provide prognostic information about the patient.

The expression and processing of two recombinant 2S albumins from soybean (Glycine max) in the yeast Pichia pastoris

Soybean seeds contain two 2S albumin storage proteins (AL1 and AL3) which may contribute to their industrial processing quality and allergenicity. We show that these proteins (AL1 and AL3) are well expressed by the methylotrophic yeast Pichia pastoris and that one of the secreted proteins (AL3) has a similar conformation and stability to that purified from soybean seeds. Further, we show that the subunits are post-translationally processed within the same loop region as the native protein but with some differences in the precise sites. This internal processing provides useful information on the endoproteolytic activity in P. pastoris. We also show that, similar to many plant allergens, the 2S albumins from soybean are stable to heat and chemical treatments.

2S storage protein gene of Douglas-fir: characterization and activity of promoter in transgenic tobacco seeds

To date a few sequences regulating expression of conifer seed-specific genes have been reported. To characterize Douglas-fir (Pseudotsuga menziesii [Mirb] Franco) 2S albumin storage protein genes, a genomic DNA sequence containing upstream promoter sequences was isolated by screening a Douglas-fir genomic library. Sequence analysis of the Douglas-fir gPm2S1 promoter revealed the presence of RY-repeated elements (GCATGC), and multiple E-box motifs (CANNTG) and ACGT-core elements, features characteristic of 2S storage protein genes in angiosperms. When fused to the GUS reporter gene, the 1.16 kb Douglas-fir 2S promoter sequence was sufficient to direct transient expression in both developing Douglas-fir embryos and maternally derived haploid megagametophytes. Analysis of this promoter construct in transgenic tobacco showed that expression was restricted to embryo and endosperm in developing seeds and was not detected in vegetative tissues of two-week-old seedlings. These results strongly suggest that both structural and regulatory elements as well as upstream signaling components controlling the expression of 2S albumin genes are highly conserved during evolution.

New Methods for Chemo-Enzymatic Galactosidation of 2S Rapeseed Protein

Two chemo-enzymatic methodologies to synthesize neoglycoproteins from rapeseed 2S protein (napin) were developed. In the first approach, glycosidases were used to catalyse 1-O-glycosylation of serine residues, whereas in the second one, 6-N-galactosylation was examined using an amino-reduction reaction between the epsilon-NH2 of lysine residues and 6-oxogalactosides (readily available by means of the oxidation reaction of the corresponding galactosides mediated by galactose oxidase). Our results indicated that glycosidases were unable to glycosylate native proteins. Conversely, this reaction was possible, although in low yields (10%), after the introduction of a hydroxyethylene spacer. The latter modified proteins were obtained via the condensation of epsilon-NH2 of lysines with ethylene carbonate in basic medium (40% yield). The second approach was much more efficient, as 61% of the lysine residues were shown to be 6-N-galactosylated using sodium cyanoborohydride as a reduction reagent.

A napin-like polypeptide from dwarf Chinese white cabbage seeds with translation-inhibitory, trypsin-inhibitory, and antibacterial activities

Napins are 1:1 disulfide-linked complexes of a smaller (ca. 4kDa) subunit and a larger (ca. 10kDa) subunit. The intent of the present study was to ascertain the production of napin by the seeds of a Brassica species that has not been examined previously, and also to explore new biological activities of the napin. A heterodimeric 11-kDa napin-like polypeptide has been isolated from Chinese white cabbage (Brassica chinensis cv dwarf) seeds with a protocol comprising ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, fast protein liquid chromatography (FPLC)-ion exchange chromatography on Mono S and FPLC-gel filtration on Superdex 75. The N-terminal sequence of the 7-kDa subunit manifests striking similarity to napin large chain, albumin and trypsin inhibitor. The N-terminal sequence of the 4-kDa subunit is homologous to napin large chain and an antimicrobial peptide. The napin-like polypeptide inhibited translation in the rabbit reticulocyte system with an IC50 of 18.5nM. This translation-inhibitory activity was stable between pH 4 and 11, and between 10 and 40 degrees C. The polypeptide inhibited trypsin with a higher potency ( IC50 = 8.5 microM) than it inhibited chymotrypsin (IC50 = 220 microM), but was devoid of ribonuclease and antifungal activities. It manifested antibacterial activity against Pseudomonas aeruginosia, Bacillus subtilis, Bacillus cereus, and Bacillus megaterium. The results revealed that the napin-like polypeptide from Chinese white cabbage seeds exhibited some potentially exploitable activities.

Analysis of proteins by CE, CIEF, and microfluidic devices with whole-column-imaging detection

The recently developed whole-column-imaging detection technique for capillary electrophoresis (CE) and capillary isoelectric focusing (CIEF), a commercial whole-column-imaged CIEF instrument and its standard operation protocol are introduced. Furthermore, new developments and applications of whole-column-imaging detection in protein-protein interaction study, in protein separation using microfluidic devices and CIEF methods without carrier ampholytes, as well as in 2D separation techniques are reviewed. Miniaturization of whole-column-imaging CIEF and axially illuminated fluorescence whole-column-imaging CIEF are also discussed.

Solution structure of RicC3, a 2S albumin storage protein from Ricinus communis

The three-dimensional structure in aqueous solution of recombinant (15)N labeled RicC3, a 2S albumin protein from the seeds of castor bean (Ricinus communis), has been determined by NMR methods. The computed structures were based on 1564 upper limit distance constraints derived from NOE cross-correlation intensities measured in the 2D-NOESY and 3D-HSQC-NOESY experiments, 70 phi torsion angle constraints obtained from (3)J(HNH)(alpha) couplings measured in the HNHA experiment, and 30 psi torsion angle constraints derived from (3)J(H)(alpha)(Ni+1) couplings measured in the HNHB experiment. The computed structures showed a RMSD radius of 0.64 A for the structural core. The resulting structure consists of five amphipatic helices arranged in a right-handed super helix, a folding motif first observed in nonspecific lipid transfer proteins. Different than the latter, RicC3 does have not an internal cavity, a fact that can be related to the exchange in the pairing of disulfide bridges in the segment.CXC. Previous attempts to determine high resolution structures of a 2S albumin protein by either X-ray crystallography or NMR methods failed because of the heterogeneity of the protein prepared from natural sources. Both 2S albumins and nonspecific lipid transfer proteins belong to the prolamine superfamily, some of whose members are food allergens. The solution structure for recombinant RicC3 determined here is a suitable representative structure for the broad family of seed 2S albumin proteins, which may help to establish meaningful relationships between structure and allergenicity. RicC3 is also the peptidic component of the immunomodulator Inmunoferon, a widely used pharmaceutical product, and its structure is expected to help understand its pharmaceutical activity.

Serological characteristics of peanut allergy in children

BACKGROUND

Food challenge is considered an excellent clinical tool for the diagnosis of specific food allergy. However in the case of peanut allergy it may be difficult to perform because of the severity of the reactions. The quantitation of a specific immunoglobulin E (IgE) response to different peanut allergens could also contribute to the improvement of the diagnosis. We characterized the IgE response to a whole peanut protein extract and to Ara h 1 and Ara h 2 in different groups of patients classified according to the severity of their allergic reactions.

METHODS

Specific serum IgE were analyzed in 96 children by enzyme-linked immunosorbent assay tests using a whole protein extract or purified peanut proteins and anti-human IgE monoclonal antibodies labeled with acetylcholinesterase.

RESULTS

A parallel was observed between levels of peanut-specific IgE and the classification in five groups and subgroups of patients upon increasing severity of symptoms, especially within the group of highest severity. Moreover, the highest frequency of positive response and the highest levels of specific IgE were observed with whole peanut protein extract.

CONCLUSION

In a retrospective evaluation of peanut allergy in children, we have shown that quantitation of peanut-specific IgE could be used to avoid a food challenge particularly in the case of severe reactions. When compared to Ara h 1 and Ara h 2, whole peanut protein extract appeared to be the most appropriate allergen to perform the test.

Sequence-specific, Golgi-dependent vacuolar targeting of castor bean 2S albumin

The targeting of the castor bean (Ricinus communis) 2S albumin precursor has been investigated by expressing cDNA in transformed tobacco (Nicotiana tabacum) leaf cells and by following biosynthesis in the native tissue. Correct targeting in both tissues was accompanied by processing of the precursor. Delivery to vacuoles was sensitive to brefeldin A (BFA) treatment in both tissues and to perturbation of COPII function in tobacco, supporting the view that transport through the Golgi is required. The targeting signal for this Golgi-dependent routing lies within the propeptide of the first heterodimer of proalbumin. This propeptide directed a normally secreted reporter protein to the vacuoles of tobacco cells in a Golgi-dependent manner in vivo, unless a critical Leu residue was mutated, supporting the view that a sequence-specific signal was needed to target a seed storage protein to the vacuoles of a vegetative cell.

A 2S albumin-homologous protein from passion fruit seeds inhibits the fungal growth and acidification of the medium by Fusarium oxysporum

Antimicrobial proteins have been isolated from a wide range of plant species. More recently, it has become increasingly clear that these types of proteins play an important role in the protection of plants. In this study, we investigate the presence of defense-related proteins from passion fruit (Passiflora edulis f. flavicarpa) seeds. Initially, seed flour was extracted for 2h (at 4 degrees C) with phosphate buffer, pH 5.5. The precipitate obtained between 0 and 70% relative ammonium sulfate saturation was re-dissolved in distilled water and heated at 80 degrees C for 15 min. The resulting suspension was clarified by centrifugation and the supernatant (F/0-70) was extensively dialyzed. A Sephadex G-50 size exclusion column was employed for further separation of proteins. The fraction with antifungal activity was pooled and submitted to CM-Sepharose cation exchange. Two proteins, named Pf1 and Pf2, were eluted in 0.1 and 0.2M of salt, respectively, and submitted to reverse-phase chromatography in HPLC. This fraction inhibited the growth, in an in vitro assay, of the phytopathogenic fungi Fusarium oxysporum and colletotrichum lindemuthianum and the yeast Saccharomyces cerevisiae and strongly inhibited glucose-stimulated acidification of the medium by F. oxysporum in a dose-dependent manner. The molecular masses of these proteins, referred to now as Pf1-RP and Pf2-RP, were obtained by MALDI-TOF spectrometry and corresponded to 12,088 Da for Pf1-RP and 11,930 Da for Pf2-RP. These proteins were also subjected to automated N-terminal amino acid sequencing. Sequence comparisons for the heavy subunit of Pf2-RP showed the presence of a protein with a high degree of homology to storage 2S albumins.

A plant-based allergy vaccine suppresses experimental asthma via an IFN-gamma and CD4+CD45RBlow T cell-dependent mechanism

Allergic asthma is currently considered a chronic airway inflammatory disorder associated with the presence of activated CD4(+) Th2-type lymphocytes, eosinophils, and mast cells. Interestingly, therapeutic strategies based on immune deviation and suppression have been shown to successfully attenuate the development of the asthma phenotype. In this investigation, we have for the first time used a genetically modified (GM) plant, narrow leaf lupin (Lupinus angustifolius L.), expressing a gene for a potential allergen (sunflower seed albumin) (SSA-lupin) to examine whether a GM plant/food-based vaccine strategy can be used to suppress the development of experimental asthma. We show that oral consumption of SSA-lupin promoted the induction of an Ag-specific IgG2a Ab response. Furthermore, we demonstrate that the plant-based vaccine attenuated the induction of delayed-type hypersensitivity responses and pathological features of experimental asthma (mucus hypersecretion, eosinophilic inflammation, and enhanced bronchial reactivity (airways hyperreactivity). The suppression of experimental asthma by SSA-lupin was associated with the production of CD4(+) T cell-derived IFN-gamma and IL-10. Furthermore, we show that the specific inhibition of experimental asthma was mediated via CD4(+)CD45RB(low) regulatory T cells and IFN-gamma. Thus, our data demonstrate that a GM plant-based vaccine can promote a protective immune response and attenuate experimental asthma, suggesting that plant-based vaccines may be potentially therapeutic for the protection against allergic diseases.

In vitro stability and immunoreactivity of the native and recombinant plant food 2S albumins Ber e 1 and SFA-8

BACKGROUND

The ability of an intact protein to reach the circulatory system may be a prerequisite to allergenicity and many allergens, particularly those from plant foods, have been found to be consistently more resistant to digestion by pepsin than other proteins.

OBJECTIVE

This study assessed the pepsinolytic stability of native 2S albumins from Brazil nut and sunflower seed and their recombinant versions produced in Pichia pastoris. The physicochemical stability of native and recombinant Brazil nut 2S albumins and recombinant sunflower seed 2S albumin was also assessed. The immunoreactivity of native Brazil nut 2S albumin and recombinant 2S albumins was compared using serum from patients allergic to Brazil nuts and animals immunized with native 2S albumins.

METHODS

Digestibility was measured in simulated gastric fluid followed by SDS-PAGE. Circular dichroism spectra were used to analyse unfolding, as proteins were denatured by temperature, pH and guanidinium chloride. Immunoreactivity was assessed by immunoblot, RAST and ELISA.

RESULTS

Brazil nut 2S albumin was significantly more resistant to proteolytic digestion than other Brazil nut proteins. It was also resistant to thermally and chemically induced denaturation. Equally high resistance to proteolytic digestion was observed with sunflower seed 2S albumin. The recombinant albumins mirrored their native counterparts in stability and immunoreactivity.

CONCLUSION

The important food allergen Brazil nut 2S albumin is as stable to digestion as is sunflower seed 2S albumin, whose allergenicity has yet to be determined. The 2S albumins and their recombinant counterparts could not be easily denatured by physicochemical treatments. The results suggest that 2S albumin is the only Brazil nut protein to reach the gut immune system intact. The production of properly folded recombinant proteins will facilitate mechanistic studies as well as diagnostic testing and antigen-based therapies.

The major peanut allergen, Ara h 2, functions as a trypsin inhibitor, and roasting enhances this function

BACKGROUND

The widespread use of peanut products, the severity of the symptoms, and its persistence in afflicted individuals has made peanut allergy a major health concern in western countries such as the United States, United Kingdom, and Canada. In a previous study, the authors showed that the allergenic properties of peanut proteins are enhanced as a result of thermal processing.

OBJECTIVE

The purpose of this investigation was to determine whether any specific functions are associated with the major peanut allergen, Ara h 2, and whether the functionality of this protein is influenced by processing. An assay was developed and used to assess structure/function changes in Ara h 2 induced by roasting and the effect of these alterations on the allergenic properties of this major peanut allergen.

METHODS

A protein domain homology search was used to determine possible functions for Ara h 2. One of the putative functions (protease inhibition) was tested by means of appropriate enzyme assays and protein gel electrophoresis. Circular dichroism was used to compare the structural properties of Ara h 2 purified from raw and roasted peanuts.

RESULTS

Ara h 2 purified from peanuts is homologous to and functions as a trypsin inhibitor. Roasting caused a 3.6-fold increase in trypsin inhibitory activity. Functional and structural comparison of the Ara h 2 purified from roasted peanuts to native and reduced Ara h 2 from raw peanuts revealed that the roasted Ara h 2 mimics the behavior of native Ara h 2 in a partially reduced form.

CONCLUSIONS

The data indicate that thermal processing might play an important role in enhancing the allergenic properties of peanuts. Not only has it previously been shown to affect the structural and allergic properties of peanut proteins but also, for the first time, the functional characteristics of an allergen. These structural and functional alterations are likely to influence the allergenicity of peanuts.

Isolation of a napin-like polypeptide with potent translation-inhibitory activity from Chinese cabbage (Brassica parachinensis cv green-stalked) seeds

A heterodimeric napin-like polypeptide was isolated from Brassica parachinensis seeds with a procedure involving ion exchange chromatography on DEAE-cellulose, affinity chromatography on Affi-gel blue gel, FPLC-ion exchange chromatography on Mono S and FPLC-gel filtration on Superdex 75. The N-terminal sequence of the 5 kDa subunit of the polypeptide (PAGPFRIPKKRKKEE) showed high homology with other 2S storage proteins like napins and albumins. The polypeptide potently inhibited translation in a cell free system with an IC50 of 6.2 nM. The translation-inhibiting activity of the polypeptide was relatively stable in the pH range 6-11 and in the temperature range 10-50 degrees C.

Measurement of peptide-specific IgE as an additional tool in identifying patients with clinical reactivity to peanuts

BACKGROUND

Peanut allergy is one of the most common food allergies, often resulting in severe reactions. Diagnostic decision levels of food-specific IgE antibody concentrations have been described. However, many patients still need to undergo oral peanut challenges because their IgE levels are in the nondiagnostic level.

OBJECTIVE

The aim of this study was to determine whether differences exist in IgE-binding epitope recognition between sensitized children with and without symptomatic peanut allergy.

METHODS

Eight peptides representing the immunodominant sequential epitopes on Ara h 1, 2, and 3 were synthesized on SPOTs membranes. Individual patient labeling was performed with sera from 15 patients with symptomatic peanut allergy and 16 patients who were sensitized but tolerant. Ten of these 16 patients had "outgrown" their allergy.

RESULTS

Regardless of their peanut-specific IgE levels, most patients with symptomatic peanut allergy showed IgE binding to the 3 immunodominant epitopes on Ara h 2. In contrast, each of these epitopes was recognized by < 10% of the tolerant patients. In addition, tolerant patients did not recognize 2 immunodominant epitopes on Ara h 1. At least 93% of symptomatic, but only 12.5% of tolerant patients, recognized 1 of these "predictive" epitopes on Ara h 1 or 2. Moreover, the cumulative IgE binding to the peanut peptides was significantly higher in patients with peanut allergy than in tolerant patients. With up to 50% of patients with peanut-specific IgE levels below diagnostic decision levels still being clinically reactive, oral food challenges could be avoided in ~90% of these patients through determination of peptide-specific IgE.

CONCLUSIONS

Determination of epitope recognition provides an additional tool to diagnose symptomatic peanut allergy, especially in children with peanut-specific IgE below diagnostic decision levels.

Persistent protective effect of heat-killed Escherichia coli producing "engineered," recombinant peanut proteins in a murine model of peanut allergy

BACKGROUND

Peanut allergy (PNA) is a life-threatening food allergy for which there is no definitive treatment.

OBJECTIVE

We investigated the long-term immunomodulatory effect of heat-killed Escherichia coli producing engineered (mutated) Ara h1, 2, and 3 (HKE-MP123) administered rectally (pr) in a murine model of PNA.

METHODS

Peanut-allergic C3H/HeJ mice received 0.9 (low dose), 9 (medium dose), or 90 (high dose) microg HKE-MP123 pr, HKE-containing vector (HKE-V) alone, or vehicle alone (sham) weekly for 3 weeks. Mice were challenged 2 weeks later. A second and third challenge were performed at 4-week intervals.

RESULTS

After the first challenge, all 3 HKE-MP123 and HKE-V-treated groups exhibited reduced symptom scores (P <.01,.01,.05,.05, respectively) compared with the sham-treated group. Interestingly, only the medium- and high-dose HKE-MP123-treated mice remained protected for up to 10 weeks after treatment accompanied by a significant reduction of plasma histamine levels compared with sham-treated mice (P <.05 and.01, respectively). IgE levels were significantly lower in all HKE-MP123-treated groups (P <.001), being most reduced in the high-dose HKE-MP123-treated group at the time of each challenge. IL-4, IL-13, IL-5, and IL-10 production by splenocytes of high-dose HKE-MP123-treated mice were significantly decreased (P <.01;.001,.001, and.001, respectively), and IFN-gamma and TGF-beta production were significantly increased (P <.001 and.01, respectively) compared with sham-treated mice at the time of the last challenge.

CONCLUSIONS

Treatment with pr HKE-MP123 can induce long-term "downregulation" of peanut hypersensitivity, which might be secondary to decreased antigen-specific T(H)2 and increased T(H)1 and T regulatory cytokine production.

Isolation and characterization of two complete Ara h 2 isoforms cDNA

BACKGROUND

Ara h 2 is a major peanut allergen recognized by IgE in more than 90% of patients. After electrophoretic separation the purified protein exists as a doublet, and sequences of one incomplete cDNA and one genomic clone for this allergen have been reported.

METHODS

Ara h 2 isoforms were purified and analyzed by mass spectroscopy, and PCR amplification products of Ara h 2 were cloned and sequenced.

RESULTS

Mass spectroscopy of purified Ara h 2 clearly identified a molecular doublet of 16,670 and 18,050 Daltons. Amplification of a peanut cDNA library using PCR primer pairs located at the amino- and carboxy-terminus revealed 2 bands separated by 50 base pairs, which we cloned and sequenced. Two types of complete cDNA clones were obtained, Ara h 2.01 and Ara h 2.02. Compared to Ara h 2.01 and the previously reported cDNA sequences, Ara h 2.02 is characterized by a 12 amino acid insertion starting at position 75 that contains a third repeat of the major IgE binding epitope DPYSPS.

CONCLUSION

We demonstrated the molecular and genetic characteristics of two Ara h 2 isoforms, revealing that one, Ara h 2.02, might be the more potent allergen.

Engineered recombinant peanut protein and heat-killed Listeria monocytogenes coadministration protects against peanut-induced anaphylaxis in a murine model

Peanut allergy (PNA) is the major cause of fatal and near-fatal anaphylactic reactions to foods. Traditional immunotherapy using peanut (PN) protein is not an option for PNA therapy because of the high incidence of adverse reactions. We investigated the effects of s.c. injections of engineered (modified) recombinant PN proteins and heat-killed Listeria monocytogenes (HKLM) as an adjuvant on anaphylactic reactions in a mouse model of PN allergy. PN-allergic C3H/HeJ mice were treated s.c. with a mixture of the three major PN allergens and HKLM (modified (m)Ara h 1-3 plus HKLM). The effects on anaphylactic reactions following PN challenge and the association with Ab levels and cytokine profiles were determined. Although all mice in the sham-treated groups exhibited anaphylactic symptoms with a median symptom score of 3, only 31% of mice in the mAra h 1-3 plus HKLM group developed mild anaphylaxis, with a low median symptom score of 0.5. Alterations in core body temperature, bronchial constriction, plasma histamine, and PN-specific IgE levels were all significantly reduced. This protective effect was markedly more potent than in the mAra h 1-3 protein alone-treated group. HKLM alone did not have any protective effect. Reduced IL-5 and IL-13, and increased IFN-gamma levels were observed only in splenocytes cultures from mAra h 1-3 plus HKLM-treated mice. These results show that immunotherapy with modified PN proteins and HKLM is effective for treating PN allergy in this model, and may be a potential approach for treating PNA.

Comparison of protein chemical and physicochemical properties of rapeseed cruciferin with those of soybean glycinin

Rapeseeds contain cruciferin (11S globulin), napin (2S albumin), and oleosin (oil body protein) as major seed proteins. The effects of oil expression and drying conditions on the extraction of these proteins from rapeseed meal were examined. The conditions strongly affected the extraction of oleosin and only weakly affected the extraction of cruciferin and napin. The protein chemical and physicochemical properties of cruciferin, the major protein present, were compared with those of glycinin (soybean 11S globulin) under various conditions. In general, cruciferin exhibited higher surface hydrophobicity, lower thermal stability, and lower and higher solubility at mu= 0.5 and mu = 0.08, respectively, than did glycinin. At the pHs (6.0, 7.6, and 9.0) and ionic strengths (mu= 0.08 and 0.5) examined, the emulsifying ability of cruciferin was worse than that of glycinin, except at mu= 0.08 and pH 7.6. The emulsifying abilities of cruciferin and glycinin did not correlate with thermal stability and surface hydrophobicity. Higher protein concentration, higher heating temperature, higher pH, and lower ionic strength were observed to produce harder gels from cruciferin. Gel hardness partly correlated with the structural stability of cruciferin.

The disulphide mapping, folding and characterisation of recombinant Ber e 1, an allergenic protein, and SFA8, two sulphur-rich 2S plant albumins

We have cloned and expressed genes encoding the allergenic brazil nut 2S albumin (Ber e 1) and the sunflower albumin 8 (SFA8) in the methylotrophic yeast Pichia pastoris. We show that both proteins were secreted at high levels and that the purified proteins were properly folded. We also showed that Ber e 1 is glycosylated during secretion and that the glycan does not interfere with the folding or immunoreactivity. The disulphide map of the Ber e 1 protein was experimentally established and is in agreement with the conserved disulphide structure of other members of the 2S albumin family. A model three-dimensional structure of the allergen was generated. During the expression studies and through mutation we have also shown that alteration of the sequences around the Kex2 endoproteolytic processing site in the expressed fusion protein can compromise the secretion by targeting part of the protein for possible degradation. The secreted production of these properly folded sulphur-rich plant albumins presents an opportunity to delineate the attributes that make an allergen and to facilitate the diagnosis and therapy of type I allergy.

Stability of recombinant 2 S albumin allergens in vitro

Two well known 2 S albumins, Ber e 1 from brazil nut and sunflower 2 S albumin 8 (SFA-8), have been expressed in a eukaryotic system and purified. Analysis of recombinant versions of Ber e 1 and SFA-8 revealed them to be significantly more resistant to digestion by pepsin than BSA, and to be stable for up to 30 min in simulated gastric fluid. Unfolding monitored by CD indicated that both proteins were also very resistant to denaturation induced by heat and low pH. These results suggest that, although the ability of 2 S albumins to reach the circulatory system may be a prerequisite for the allergenicity of this group of proteins, stability is just one of a number of characteristics that provoke a selective immune response.