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

Screening and Interaction Analysis of Shark-Derived Nanobodies against Crayfish Major Allergen Pro c 2

Pro c 2 (arginine kinase) is a major allergen in crayfish (Procambarus clarkii). Shark-derived variable domains of new antigen receptors (VNARs) have advantages in developing allergen detection and immunotherapy. This study constructed a VNAR domain library from Chiloscyllium plagiosum immunized with Pro c 2. Three VNARs (VNAR-11, VNAR-20, and VNAR-29) against Pro c 2 obtained by screening the library were expressed in the HEK293F cells, fusing with the immunoglobulin (Ig) G1 Fc fragment (VNAR-Fc-11, VNAR-Fc-29, and VNAR-Fc-20). The VNAR-Fc fusions bound to Pro c 2 with an affinity KD ranging from 0.2131 ∼ 465.3 μM, with the ability to inhibit patients' IgE binding to Pro c 2. VNAR-20 and VNAR-29 displayed more stable binding with Pro c 2 during molecular dynamics simulation. The binding sites of the VNARs are distributed in the conserved IgE epitopes of arginine kinase. These achievements indicate the application potential of VNARs in allergen detection and allergy therapeutics.

Identification and Validation of Key Amino Acids in IgE Linear Epitopes of β-Lactoglobulin: Comparison of Recognition Patterns of Chinese Bovine Milk-Allergic Sera with Different Symptoms

β-lactoglobulin (BLG) is the primary allergen in bovine milk allergy. The identification of key amino acids in the BLG epitopes has not been comprehensive due to differences in identification methods, patient symptoms, and population characteristics. In this study, bioinformatics predictions were conducted for key amino acids based on two potential IgE linear epitopes in BLG. Then, the peptide AA30-43 was confirmed as an IgE linear epitope through alanine scanning mutagenesis and peptide microarray assays, with four key amino acids (A34, A37, R40, and V41) common to different symptoms being identified. Moreover, symptom-specific key amino acids were identified. Serine (S30) and aspartic acid (D33) are the key amino acids for cutaneous allergy, while food allergy sera showed a preference for recognizing leucines in different positions (L31 and L39). Additionally, mutant peptides (R40, V41, L39, and D33) showed an obvious decrease in digestive stability compared with the epitope. Finally, the results of the KU812 cell degranulation model validated the critical role of the amino acids in allergenicity. These findings offer significant advantages for advancing both immune tolerance therapies and hypoallergenic milk product development, which hold significant implications for further research, prevention, and treatment of bovine milk allergy.

A Crystal Structure of Pro c 2 Provides Insights into Cross-Reactivity of Aquatic Allergens from the Phosphagen Kinase Family

Arginine kinase (AK) from the phosphagen kinase family is a cross-reactive shellfish allergen. Structurally related cross-reactive allergens are involved in the pathogenesis of allergic symptoms. This study aimed to unravel the cross-reactivity of AK from a structural perspective. The crystal structure of Procambarus clarkii AK (Pro c 2) was resolved at 1.57 Å resolution, which showed a well-conserved structure not only to shellfish AKs but also to fish creatine kinase (CK), another allergen from the phosphagen kinase family. In Western blot, the CK corresponding protein in fish muscles was found to be reactive with AK-specific immunoglobulin (Ig) G. Recombinant Pro c 2 (rPro c 2) and CKs from Lateolabrax japonicus (rCK-L) and Ctenopharyngodon idell (rCK-C) were then produced, and the IgE reactivity of rCK-L and rCK-C, as well as their IgG/IgE cross-reactivity with rPro c 2, was confirmed by immunological assays. This study demonstrated the cross-reactivity among aquatic allergens from the phosphagen kinase family due to their structural similarity.

Development of Hypoallergenic Derivatives of Cra a 1 with B Cell Epitope Deletion and T Cell Epitope Retention

Tropomyosin was reported as an important allergen in Crassostrea angulata and designated as Cra a 1. The localization of the T cell epitopes and the reduction of the immunoreactivity of Cra a 1 are still lacking. In this study, four T cell epitopes were identified by using wild-type Cra a 1 (wtCra a 1)-immunized mouse splenocytes cultured with synthetic peptides. The immunoreactivity was maintained after chemical denaturation treatment, indicating that the linear epitope is an immunodominant epitope of wtCra a 1. Furthermore, the hypoallergenic derivative (mCra a 1) was developed by the deletion of linear B cell epitopes and retention of T cell epitopes. mCra a 1 could stimulate CD4+T cell proliferation and upregulate interleukin-10 secretion. Overall, basophil activation by mCra a 1 was low, but its ability to induce T cell proliferation was retained, suggesting that mCra a 1 may serve as a viable candidate for treating oyster allergy.

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

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

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

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

Immunoglobulin E Epitope Mapping and Structure-Allergenicity Relationship Analysis of Crab Allergen Scy p 9

Filamin C is an allergen of Scylla paramamosain (Scy p 9), and six IgE linear epitopes of the allergenic predominant region had previously been validated. However, the IgE epitope and structure-allergenicity relationship of Scy p 9 are unclear. In this study, a hydrophobic bond was found to be an important factor of conformation maintaining. The critical amino acids in the six predicted conformational epitopes were mutated, and the IgE-binding capacity and surface hydrophobicity of four mutants (E216A, T270A, Y699A, and V704A) were reduced compared to Scy p 9. Ten linear epitopes were verified with synthetic peptides, among which L-AA187-205 had the strongest IgE-binding capacity. In addition, IgE epitopes were mapped in the protruding surface of the tertiary structure, which were conducive to binding with IgE and exhibited high conservation among filamin genes. Overall, these data provided a basis for IgE epitope mapping and structure-allergenicity relationship of Scy p 9.