Identification,\nPurification, and Characterization\nof Kunitz-Type Protease Inhibitors from White-Fleshed Dragon Fruit\n(Selenicereus undatus) and Red-Fleshed\nDragon Fruit (Selenicereus costaricensis) Seeds as Novel Food Allergens

There have been clinical reports of allergies to dragon\nfruits.\nHowever, little is known about the allergens that trigger these reactions.\nThis study aimed to investigate novel allergens in dragon fruits.\nThe peptide mass fingerprints of two purified natural allergens were\nidentified by LC–MS/MS with chymotrypsin proteolysis. The complete\namino acid sequences of the allergens were deduced from cDNA amplicon\nsequences. The coding sequences of two allergens were inserted in\nthe expression vector pColdI, and recombinant allergens were produced\nin Escherichia coli. Circular dichroism\nwas performed to analyze the secondary structures of natural and recombinant\nallergens. Our results identified two novel allergens as Kunitz-type\nprotease inhibitors. Recombinant allergens exhibited well-folded structures,\npredominantly composed of β-sheets, similar to their natural\ncounterparts. IgE reactivity analysis with sera from ten patients\nprimarily sensitized to dragon fruit indicated that Kunitz-type protease\ninhibitors are major allergens in dragon fruits. These results improve\nour understanding of allergen sources and provide important insights\ninto the allergenicity of proteins from different species.