The major peanut allergen Ara h 1 and its cleaved-off N-terminal peptide; possible implications for peanut allergen detection

Ara h 1 was purified from raw peanuts (Arachis hypogaea L.) in the presence or absence of protease inhibitors. N-Terminal amino acid sequences were determined after western blotting. Both purification procedures proved to be very consistent and resulted in identical chromatographic and electrophoretic behavior of Ara h 1 and in the isolation of identical proteins of similar to64 kDa with RS/H_PPGERTRG as the N-terminal amino acid sequence. Consequently, purified Ara h 1 appears to be truncated at the N-terminal side. The observations strongly suggest that Ara h 1 occurs physiologically as a protein of which the first 84 and 78 amino acids, respectively, are cleaved off in planta upon maturation of the protein. On the basis of epitope mapping, the cleaved-off N-terminal peptide contains three allergenic epitopes, of which two are major. These truncated epitopes will go undetected in assays when purified Ara h 1 from peanuts is used as reference material. Patients' sera, however, contain IgE-type antibodies against the epitopes that are contained in the cleaved-off peptide, implying that the peptide, or part of it, is still present in peanuts that are consumed. Possible consequences of this exposure to these three epitopes are discussed. On the basis of literature data the cleaved-off peptide is hypothesized to have antifungal activity.