Identification of the amino-terminal fragment of Ara h 1 as a major target of the IgE-binding activity in the basic peanut protein fraction

Abstract

Background: Small, basic peanut proteins are often poorly extracted in pH-neutral buffers that are optimal for the extraction of peanut storage proteins such as Ara h 1. As a result, such proteins are easily missed as potential allergens.

Objective: To analyse the allergenic composition of the basic peanut protein (BPP) fraction.

Methods: A peanut extract prepared at pH 4 was fractionated by physicochemical procedures. Chemical analysis was performed by SDS-PAGE and mass spectrometry. Because immunoblotting was found to be inefficient for most of these small basic proteins, IgE-binding activity was measured by coupling the fractions to CNBr-activated Sepharose, followed by incubation with sera from 55 Dutch peanut-allergic children and ¹²⁵ I-labelled anti-IgE.

Results: Most IgE reactivity of the BPP fraction was due to the 5-7 kDa amino-terminal fragment of Ara h 1. This finding was confirmed by the use of the fragment in recombinant form, to which 25/55 of the sera was IgE-positive.

Conclusion: The amino-terminal fragment of Ara h 1, a member of a family of small anti-microbial proteins, is an allergen independent of the carboxy-terminal fragment of Ara h 1.

Keywords: IgE; allergens and epitopes; food allergy; immunologic tests.