Identification and Characterisation of the IgE-Binding Proteins 2S Albumin and Conglutin γ in Almond (Prunus dulcis) Seeds

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Abstract
Background: Almond proteins can cause severe anaphylactic reactions in susceptible individuals. The aim of this study was the identification of IgE-binding proteins in almonds and the characterisation of these proteins by N-terminal sequencing. Methods: Five sera were selected from individuals with a positive reaction to food challenge. Sodium dodecylsulphate-polyacrylamide gel electrophoresis and immunoblotting were performed on almond seed proteins. Purified IgE-binding proteins were tested for immunoblot inhibition with sera pre-incubated with extracts of hazelnut and walnut. Results: N-terminal sequences of the 12-, 30- and 45-kD proteins were obtained. The 45- and 30-kD proteins shared the same N terminus, with 60% homology to the conglutin γ heavy chain from lupine seed (Lupinus albus) and to basic 7S globulin from soybean (Glycine max). The sequences of the N-terminal 12-kD protein and of an internal peptide obtained by endoproteinase digestion showed good homology to 2S albumin from English walnut (Jug r 1). Immunoblot inhibition experiments were performed and IgE binding to almond 2S albumin and conglutin γ was detected in the presence of cross-reacting walnut or hazelnut antigens. Conclusions: Two IgE-binding almond proteins were N-terminally sequenced and identified as almond 2S albumin and conglutin γ. Localisation and conservation of IgE binding in a 6-kD peptide obtained by endoproteinase digestion of 2S albumin was shown.