Molecular and immunological characterization of β′-component (Onc k 5), a major IgE-binding protein in chum salmon roe

Abstract

Salmon roe has a high allergic potency and often causes anaphylaxis in Japan. The major allergic protein of salmon roe is β'-component, which is a 35kDa vitellogenin fragment consisting of two subunits. To elucidate structural information and immunological characteristics, β'-component and the subunit components were purified from chum salmon (Onchorhincus keta) roe and vitellogenin-encoding mRNA was used to prepare β'-component subunit-encoding cDNA. This was PCR-amplified, cloned and sequenced and the deduced amino acid sequence compared with partial sequences of β'-component obtained by peptide mapping. The recombinant β'-component subunit was produced by bacterial expression in Escherichia coli and its IgE-binding ability was measured by ELISA using the sera of a patient allergic to salmon roe. This was then compared with that of the native β'-component with and without carboxymethylation. Following successful cloning of the cDNA encoding the β'-component subunit, 170 amino acid residues were deduced and matched with the amino acid sequences of 121 and 88 residues in the 16kDa and 18kDa subunits, respectively. The sequences of both β'-component subunits were almost identical, and the predicted secondary structure of the β'-component showed a high content of β-pleated sheets and no α-helices. There was no difference in IgE-binding ability between the native and recombinant β'-component subunits at the same protein concentration, regardless of carboxymethylation. In conclusion, β'-component is a homodimer protein composed of two isoform subunits having the same level of IgE-binding ability and, therefore, allergenic identity.

Development of an enzyme-linked immunosorbent assay system for detecting β′-component (Onk k 5), a major IgE-binding protein in salmon roe

“…2, chum salmon β"-component as an immunized antigen showed a high purity. Lipovitellin heavy chain (around 90 kDa) was found to be the predominant component in all fish yolk extracts, and the 16 kDa and 18 kDa subunits of β"-component (Shimizu et al, 2014) were observed in chum salmon YEx. In the immunoblot analysis (Lane3), protein components detected by anti-β(Rabbit) were also found in the all other fish YEx, except for Pacific herring.…”

“…β′-component has been registered as a new allergen named "Onc k 5" in the official allergen list of the World Health Organization and International Union of 6 Immunological Societies Allergen Nomenclature Subcommittee in 2012 (http://www.allergen.org/). β′-component is a homodimer protein composed of two isoform subunits with similar allergenic identity (Shimizu et al, 2014), and the IgE-binding sites (IgE epitopes) in β′-component showed strong proteolytic resistance (Fujita et al, 2012), which may account for its strong allergenicity as a food allergen.…”

Fish Allergy Management: From Component-Resolved Diagnosis to Unmet Diagnostic Needs

“…Ingestion of fish roe may also lead to allergic sensitization and clinical allergy. The allergen Onc k 5 (chum salmon) is vitellogenin, a 118 kDa protein and precursor of yolk proteins [74]. Roe allergens from different fish species are cross-reactive but there is no cross-reactivity to hen's egg or fish muscle allergens.…”

Salmon roe‐specific serum IgE predicts oral salmon roe food challenge test results

“…In Japan, SR is the fifth most common food allergen , and it can cause anaphylactic reactions in small children . Using sera from several SR‐allergic patients, the beta‐component was identified as the main allergen . There is no IgE cross‐reactivity between SR and hen's egg allergies; nevertheless, in Japan, many patients with hen's egg allergies eliminate SR because SR is ‘an egg’ of fish.…”

“…Nevertheless, the main allergen for SR was not egg phosvitin. The beta‐component was identified as the main allergen. There was cross‐reactivity between SR and herring roe, but no relationship between SR and hen's egg .…”