1D-, 2D-Gel Electrophoresis, Immunoblotting, and Enzyme-Linked Immunosorbent Assay (ELISA) for the Study of Food Allergens

Protein-based methods have been fundamental for the study of food allergens, not only from a mechanistic and diagnostic point of view, but especially with respect to allergen management and food safety. In this chapter, four individual protocols are suggested, relying on one-dimensional, two-dimensional gel electrophoresis, immunoblotting, and enzyme-linked immunosorbent assay (ELISA). The particularities of the proposed protocols are focused on previous research targeting specific allergenic foods, with cow's milk proteins as case studies. Data on the importance of protein extraction and the use of different animal-raised antibodies and/or sera of food-allergic patients are also critically discussed within method development and optimization. The protocols herein described are successful examples applied to the study of cow's milk allergens in complex matrices, although they can be easily developed and optimized for any food allergen or allergenic food.

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.

Mechanism of Cold Plasma Combined with Glycation in Altering IgE-Binding Capacity and Digestion Stability of Tropomyosin from Shrimp

Tropomyosin (TM) is a major crustacean allergen, and the present studies have tried to reduce its allergenicity by processing technologies. However, most research stopped on the allergenicity and structure of allergens, while information about epitopes was less. In this study, we first investigated the effects of cold plasma (CP) combined with glycation (CP-G) treatment on the processing and trypsin cleavage sites of TM from shrimp (Penaeus chinensis). The results showed a significant reduction in the IgE-binding capacity of TM after CP-G treatment, with a maximum reduction of 30%. This reduction was associated with the combined effects: modification induced by CP destroyed the core helical structure (D137 and E218) and occupied the potential glycation sites, leading to sequent glycation on conserved areas of TM, especially the epitope L130-Q147. Additionally, CP-G treatment decreased the digestion stability of TM by increasing the number of cleavage sites of trypsin and improving the efficiency of some sites, including K5, K6, K30, and R133, resulting in a lower IgE-binding capacity of digestion products, which fell to a maximum of 20%. Thus, CP-G is a valuable and reliable processing technology for the desensitization of aquatic products.

IgE Epitope Analysis for Scy p 1 and Scy p 3, the Heat-Stable Myofibrillar Allergens in Mud Crab

Tropomyosin (Scy p 1) and myosin light chain (Scy p 3) are investigated to be important heat-stable allergens in Scylla paramamosain. However, the epitopes of Scy p 1 and Scy p 3 are limited. In this study, recombinant Scy p 1 and Scy p 3 had similar IgE-binding capacity to natural proteins. Mimotopes of Scy p 1 and Scy p 3 were analyzed by bioinformatics, phage display, and one-bead-one-compound technology. Ten linear epitopes of Scy p 1 and seven linear epitopes of Scy p 3 were identified by synthetic peptides and inhibition dot blot. Meanwhile, three conformational epitopes of Scy p 1 and seven conformational epitopes of Scy p 3 were verified by site-directed mutagenesis and the serological test. Furthermore, strong IgE-binding epitopes of Scy p 1 and Scy p 3 were conserved in multiple crustaceans. Overall, these epitopes could enhance our understanding of crab allergens, which lay the foundation for a cross-reaction.

Effect of Point Mutations on Structural and Allergenic Properties of the Lentil Allergen Len c 3

Plant lipid transfer proteins (LTPs) are known to be clinically significant allergens capable of binding various lipid ligands. Recent data showed that lipid ligands affected the allergenic properties of plant LTPs. In this work, we checked the assumption that specific amino acid residues in the Len c 3 structure can play a key role both in the interaction with lipid ligands and IgE-binding capacity of the allergen. The recombinant analogues of Len c 3 with the single or double substitutions of Thr41, Arg45 and/or Tyr80 were obtained by site-directed mutagenesis. All these amino acid residues are located near the “bottom” entrance to the hydrophobic cavity of Len c 3 and are likely included in the IgE-binding epitope of the allergen. Using a bioinformatic approach, circular dichroism and fluorescence spectroscopies, ELISA, and experiments mimicking the allergen Len c 3 gastroduodenal digestion we showed that the substitution of all the three amino acid residues significantly affected structural organization of this region and led both to a change of the ligand-binding capacity and the allergenic potential of Len c 3.

Combined effects of pH and thermal treatments on IgE-binding capacity and conformational structures of lectin from black kidney bean (Phaseolus vulgaris L.)

Combined effects of pH and thermal treatments on black kidney bean lectin (BKBL) were investigated by response surface methodology (RSM). Low-pH (1.0, 2.0, 3.0) incubation decreased hemagglutination activity (HA) and IgE-binding capacity, but the activities would be restored when the lectin was treated by pH shifting to 7.2. Conformational structure analyses indicated that low-pH induced protein unfolding and pH-shifting treatment resulted in a limited structural rearrangement. Mild heating, such as 60 °C for 3 min, slightly increased the HA and IgE-binding activities of pH shifted BKBL, but no obvious effects in the pH 1.0 incubated BKBL. High-temperature and long-time treatment might induce the protein aggregation, further decreased HA and IgE-binding capacities. RSM results showed both IgE-binding capacity and HA were the lowest under the combination of pH 1.0 incubation with 80 °C heating for 15 min or pH shifting from 1.0 to 7.2 with 100 °C heating for 10 min.

Glycation of β-lactoglobulin under dynamic high pressure microfluidization treatment: Effects on IgE-binding capacity and conformation

The effects of dynamic high-pressure microfluidization (DHPM) (80, 120, and 160MPa) treatment and glycation with galactose on the IgE-binding capacity and conformation of β-lactoglobulin (β-Lg) were investigated. The binding capacity of immunoglobulin E (IgE) from patients' sera with cow's milk allergy on β-Lg glycated with galactose decreased after DHPM treatment. β-Lg treated after different DHPM methods and pressures yielded a significant discrepancy in IgE-binding capacity. When β-Lg was pretreated by DHPM, the IgE-binding capacity of β-Lg-galactose conjugates decreased with increasing pressure; however, the conjugates showed higher IgE-binding capacity at 120MPa than that at 80 and 160MPa when the β-Lg-galactose mixture was treated by DHPM. Results of thermal properties, intrinsic fluorescence spectroscopy, surface hydrophobicity, and circular dichroism (CD) spectra indicated the occurrence of protein unfolding, as well as the tertiary and secondary structural changes of β-Lg. The results suggested pretreatment by DHPM and glycation with galactose was a promising approach for eliminating the IgE-binding capacity of β-Lg.