Abstract
Hazelnut is one of the most frequent causes of food allergy. The major hazel allergen in Northern Europe is Cor a 1, which is homologous to the major birch pollen allergen Bet v 1. Both allergens belong to the pathogenesis related class PR-10. We determined the solution structure of Cor a 1.0401 from hazelnut and identified a natural ligand of the protein. The structure reveals the protein fold characteristic for PR-10 family members, which consists of a seven-stranded antiparallel β-sheet, two short α-helices arranged in V-shape and a long C-terminal α-helix encompassing a hydrophobic pocket. However, despite the structural similarities between Cor a 1 and Bet v 1, they bind different ligands. We have shown previously that Bet v 1 binds to quercetin-3-O-sophoroside. Here, we isolated Cor a 1 from hazel pollen and identified the bound ligand, quercetin-3-O-(2“-O-β-D-glucopyranosyl)-β-D-galactopyranoside, by mass spectrometry and nuclear magnetic resonance spectroscopy (NMR). NMR experiments were performed to confirm binding. Remarkably, although it has been shown that PR-10 allergens show promiscuous binding behaviour in vitro, we can demonstrate that Cor a 1.0401 and Bet v 1.0101 exhibit highly selective binding for their specific ligand but not for the respective ligand of the other allergen.
Highlights
Allergy to hazel is very common in Europe[1,2] and has even been found to be the most frequent cause of IgE-mediated food allergy[3,4,5]
The structure of Cor a 1.0401 showed the overall fold typical for PR-10 allergens, consisting of a seven-stranded antiparallel β-sheet followed by a long C-terminal helix, which is enclosed by two shorter helices arranged in V-shape that comprise a hydrophobic pocket (Fig. 1A; Table 1)
These regions consist of loops which, to the strawberry allergen Fra a 1 probably show dynamic behaviour on unfavorable timescales to broaden nuclear magnetic resonance spectroscopy (NMR) signals beyond detection[35]
Summary
Allergy to hazel is very common in Europe[1,2] and has even been found to be the most frequent cause of IgE-mediated food allergy[3,4,5]. In certain plant tissues that have higher risks of being attacked by insects, fungi or of being damaged by UV-radiation, PR-10 proteins are expressed constitutively[14]. They are encoded by multiple genes and occur as a mixture of different isoallergens with >67% sequence identity and variants (formerly called isoforms) thereof, which share a very high sequence identity of >90%15. Different Cor a 1 isoallergens and variants have been identified in hazel pollen as well as in hazelnut and hazel leaves[21]. Bet v 1 has been extensively studied biochemically[16,24,25,26,27] as well as immunologically[25,28,29,30,31], the exact physiological role of this protein and its homologs derived from different plants remains elusive
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