Homology modelling of the major peanut allergen Ara h 2 and surface mapping of IgE-binding epitopes (original) (raw)
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Journal of immunology (Baltimore, Md. : 1950), 2002
Hypersensitivity to peanuts is a reaction mediated by IgE Abs in response to several peanut protein allergens. Among these allergenic proteins, Ara h 2 is one of the most commonly recognized allergens. Ara h 2 is a 17-kDa protein that has eight cysteine residues that could form up to four disulfide bonds. Circular dichroism studies showed substantial changes in the secondary and tertiary structures of the reduced Ara h 2 as compared with the native protein. Upon treatment with trypsin, chymotrypsin, or pepsin, a number of relatively large fragments are produced that are resistant to further enzymatic digestion. These resistant Ara h 2 peptide fragments contain intact IgE-binding epitopes and several potential enzyme cut sites that are protected from the enzymes by the compact structure of the protein. The enzyme-treated allergen remains essentially intact despite the action of proteases until the fragments are dissociated when the disulfide linkages are reduced. Amino acid sequence ...
Journal of Agricultural and Food Chemistry, 2005
Although many sequences and linear IgE epitopes of allergenic proteins have been identified and archived in databases, structural and physicochemical discriminators that define their specific properties are lacking. Current bioinformatics tools for predicting the potential allergenicity of a novel protein use methods that were not designed to compare peptides. Novel tools to determine the quantitative sequence and three-dimensional (3D) relationships between IgE epitopes of major allergens from peanut and other foods have been implemented in the Structural Database of Allergenic Proteins (SDAP; http://fermi.utmb.edu/SDAP/). These peptide comparison tools are based on fivedimensional physicochemical property (PCP) vectors. Sequences from SDAP proteins similar in their physicochemical properties to known epitopes of Ara h 1 and Ara h 2 were identified by calculating property distance (PD) values. A 3D model of Ara h 1 was generated to visualize the 3D structure and surface exposure of the epitope regions and peptides with a low PD value to them. Many sequences similar to the known epitopes were identified in related nut allergens, and others were within the sequences of Ara h 1 and Ara h 2. Some of the sequences with low PD values correspond to other known epitopes. Regions with low PD values to one another in Ara h 1 had similar predicted structure, on opposite sides of the internal dimer axis. The PD scale detected epitope pairs that are similar in structure and/or reactivity with patient IgE. The high immunogenicity and IgE reactivity of peanut allergen proteins might be due to the proteins' arrays of similar antigenic regions on opposite sides of a single protein structure. ]. Figure 1. SDAP-based methodology used to identify sequences similar to known epitopes of the peanut allergens.
Structure of the Major Peanut Allergen Ara h 1 May Protect IgE-Binding Epitopes from Degradation
The Journal of Immunology, 2000
In the past decade, there has been an increase in allergic reactions to peanut proteins, sometimes resulting in fatal anaphylaxis. The development of improved methods for diagnosis and treatment of peanut allergies requires a better understanding of the structure of the allergens. Ara h 1, a major peanut allergen belonging to the vicilin family of seed storage proteins, is recognized by serum IgE from >90% of peanut-allergic patients. In this communication, Ara h 1 was shown to form a highly stable homotrimer. Hydrophobic interactions were determined to be the main molecular force holding monomers together. A molecular model of the Ara h 1 trimer was constructed to view the stabilizing hydrophobic residues in the three dimensional structure. Hydrophobic amino acids that contribute to trimer formation are at the distal ends of the three dimensional structure where monomer-monomer contacts occur. Coincidentally, the majority of the IgE-binding epitopes are also located in this region, suggesting that they may be protected from digestion by the monomer-monomer contacts. On incubation of Ara h 1 with digestive enzymes, various protease-resistant fragments containing IgE-binding sites were identified. The highly stable nature of the Ara h 1 trimer, the presence of digestion resistant fragments, and the strategic location of the IgE-binding epitopes indicate that the quaternary structure of a protein may play a significant role in overall allergenicity.
Degradation 1 May Protect IgE-Binding Epitopes from Structure of the Major Peanut Allergen Ara h
2000
In the past decade, there has been an increase in allergic reactions to peanut proteins, sometimes resulting in fatal anaphylaxis. The development of improved methods for diagnosis and treatment of peanut allergies requires a better understanding of the structure of the allergens. Ara h 1, a major peanut allergen belonging to the vicilin family of seed storage proteins, is recognized by serum IgE from >90% of peanut-allergic patients. In this communication, Ara h 1 was shown to form a highly stable homotrimer. Hydrophobic interactions were determined to be the main molecular force holding monomers together. A molecular model of the Ara h 1 trimer was constructed to view the stabilizing hydrophobic residues in the three dimensional structure. Hydrophobic amino acids that contribute to trimer formation are at the distal ends of the three dimensional structure where monomer-monomer contacts occur. Coincidentally, the majority of the IgE-binding epitopes are also located in this region, suggesting that they may be protected from digestion by the monomer-monomer contacts. On incubation of Ara h 1 with digestive enzymes, various protease-resistant fragments containing IgE-binding sites were identified. The highly stable nature of the Ara h 1 trimer, the presence of digestion resistant fragments, and the strategic location of the IgE-binding epitopes indicate that the quaternary structure of a protein may play a significant role in overall allergenicity.
Molecular Immunology, 2009
Eight distinct sequential IgE-binding epitopes were identified along the amino acid sequence of Ara h 3 using the Spot technology. They essentially correspond to preferencially electropositive regions exposed on the molecular surface of the protein. A few IgE-binding epitopes are coalescent to create more extended IgE-binding regions exposed on the surface of the allergen. Ara h 3 contains a core region corresponding to the cupin motifs and predicted to be preserved upon the trypsin and chymotrypsin attack in the gastro-intestinal tract. Some of the identified IgE-binding epitopes should remain unaltered in the core region to subsequently interact with the local immune system. They most probably account for the strong allergenic potency of Ara h 3. Most of the identified IgE-binding epitopes of Ara h 3 readily differ from the corresponding regions of other legume and tree-nut legumin allergens except for epitope #1 and #7 which are rather conserved essentially in other allergens. These structurally related epitopes could account for some cross-reactions occurring between Ara h 3 and other legumin allergens.
Linear IgE epitope mapping of the English walnut (Juglans regia ) major food allergen, Jug r 1
Journal of Allergy and Clinical Immunology, 2002
Background: Peanut and tree nut allergies can be life-threatening, and they appear to be growing in prevalence. Jug r 1, a 2S albumin seed storage protein, was previously characterized as a major English walnut food allergen. Objective: We sought to identify the linear IgE-binding epitopes of Jug r 1 and to determine which, if any, amino acids are necessary for this binding to occur. Methods: Pools of sera from walnut-allergic patients and overlapping peptides synthesized on an activated cellulose membrane were used to screen for IgE-binding epitopes. Mutational analysis of the immunodominant epitope was carried out through single and multisite amino acid substitutions. Inhibition assays were performed through use of affinity-purified IgE, soluble forms of the epitope peptide, and the recombinant 2S albumin, rJug r 1. Results: One immunodominant linear epitope was identified. Amino acid mutations to the epitope demonstrated that the residues RGEE, at positions 36 through 39, were minimally required for IgE binding. Probing of this epitope with sera from each of 20 patients revealed 15 of the sera to be positive. Binding of patients' IgE to the epitope was inhibited with a soluble form of the peptide; however, soluble peptide did not completely inhibit the binding of IgE to the intact rJug r 1. Conclusion: One major linear IgE-reactive epitope and its critical core amino acid residues have been identified. Mutation of any of these core amino acids resulted in loss of IgE binding to the epitope, and this points toward the feasibility of reducing allergenicity in genetically modified walnuts. However, strong evidence for the existence of conformational epitopes was also obtained. (J Allergy Clin Immunol 2002;109:143-9.)
Epitope mapping of the major allergen 2S albumin from pine nut
Food Chemistry, 2021
The epitopes of the major allergen of pine nut, Pin p 1, were analyzed using a peptide library and sera from patients with clinical allergy to pine nut in order to deepen into the allergenic characteristics of Pin p 1. Analyses of epitope similarities and epitopes location in a 3D-model were also performed. Results showed that three main regions of Pin p 1 containing 5 epitopes were recognized by patient sera IgE. The epitopes of Pin p 1 had important similarities with epitopes of allergenic 2S albumins from peanut (Ara h 2 and 6) and Brazil nut (Ber e 1). The epitopes of Pin p 1 were found in α-helices and coils in the 3D protein structure. Interestingly, all epitopes were found to be well-exposed in the protein surface, which suggests facile access for IgE-binding to the structure of Pin p 1 which is known to be highly resistant.
Biochimie, 2005
Three-dimensional models of the major vicilin allergens from peanut (Ara h 1), lentil (Len c 1) and pea (Pis s 1), were built by homologybased modelling from the X-ray coordinates of the structurally closely related soybean b-conglycinin. All the allergen monomers exhibit the typical cupin motif made of two modules related by a pseudo-dyad axis. Each module consists of a b-barrel core domain associated to a loop domain which mainly contains a-helices. The three cupin motifs are assumed to be arranged in a homotrimeric structure similar to that observed in b-conglycinin, phaseolin or canavalin. Most of the sequential B-cell epitopes characterized on the C-terminus of the Ara h 1 allergen are well conserved in both Len c 1 and Pis s 1 allergens. They occupy very comparable areas on the molecular surface of the allergens and exhibit a similar three-dimensional conformation. This antigenic community readily accounts for the IgE-binding crossreactivity commonly observed between the vicilin allergens from edible legume seeds. The clinical implication of this cross-reactivity is addressed for a definite diagnosis of legume seed allergy.
Biochemical Journal, 2006
Resistance to proteolytic enzymes and heat is thought to be a prerequisite property of food allergens. Allergens from peanut (Arachis hypogaea) are the most frequent cause of fatal food allergic reactions. The allergenic 2S albumin Ara h 2 and the homologous minor allergen Ara h 6 were studied at the molecular level with regard to allergenic potency of native and protease-treated allergen. A high-resolution solution structure of the protease-resistant core of Ara h 6 was determined by NMR spectroscopy, and homology modelling was applied to generate an Ara h 2 structure. Ara h 2 appeared to be the more potent allergen, even though the two peanut allergens share substantial cross-reactivity. Both allergens contain cores that are highly resistant to proteolytic digestion and to temperatures of up to 100 °C. Even though IgE antibody-binding capacity was reduced by protease treatment, the mediator release from a functional equivalent of a mast cell or basophil, the humanized RBL (rat bas...