The amyloid fold of Gad m 1 epitopes governs IgE binding.

Rosa Sánchez,Ana Castro,Santiago Quirce,Javier Martínez,María Gasset,María Pedrosa,Rosa Rodríguez-Pérez

doi:10.1038/srep32801

Abstract

Amyloids are polymeric structural states formed from locally or totally unfolded protein chains that permit surface reorganizations, stability enhancements and interaction properties that are absent in the precursor monomers. β-Parvalbumin, the major allergen in fish allergy, forms amyloids that are recognized by IgE in the patient sera, suggesting a yet unknown pathological role for these assemblies. We used Gad m 1 as the fish β-parvalbumin model and a combination of approaches, including peptide arrays, recombinant wt and mutant chains, biophysical characterizations, protease digestions, mass spectrometry, dot-blot and ELISA assays to gain insights into the role of amyloids in the IgE interaction. We found that Gad m 1 immunoreactive regions behave as sequence-dependent conformational epitopes that provide a 1000-fold increase in affinity and the structural repetitiveness required for optimal IgE binding and cross-linking upon folding into amyloids. These findings support the amyloid state as a key entity in type I food allergy.

Highlights

Region I overlaps the sequence predicted as the cross-βsheet forming segment in helix A, whereas regions III and IV overlap the immunologically reactive sites located on the junctions between the AB and Circular dichroism (CD) domains and between the CD and EF domains[29,36]
For food allergens that undergo drastic environmental changes during gastrointestinal transit, these structural templates are merely snapshots of the protein life and other nonnative structures can be formed and change their interaction repertoire. One such structural state is the amyloid state that confers a polymeric trait required for multivalent interactions through the spine structure and growth properties
Only Gad m 1 amyloidogenesis was studied from the allergenic point of view, revealing the IgE binding capacity of the assemblies[36,45,46,47,48,49,50]

Summary

Introduction

These results indicate that the Gad m 1 chain contains two major IgE binding sites (regions II and IV), which are flanked and overlapped by sequences with amyloid-forming capacity (Fig. 2a). We modified the sequences with a predicted amyloid-forming capacity identified by the ZipperDB analysis as regions A, C and E to uncouple amyloid formation from IgE binding without disrupting the linear epitopes (Figs 2a and 3).

Results

Conclusion