IDENTIFICATION OF ACTINIDIN AS THE MAJOR ALLERGEN OF KIWI FRUIT

Background: Allergic reactions to fruits and vegetables are among the most frequent food allergies in adults. Kiwi fruit (Actinidia chinensi s) is commonly involved, causing local mucosal, systemic, or both type s of symptoms by an IgE-mediated mechanism. In a previous study on 30 patients allergic to kiwi, we identified a major allergen of 30 kd aga inst which all sera tested clearly reacted. Other allergens were detec ted at 12, 24, and 28 kd. Objective: The aim of this study was to full y characterize the major kiwi fruit allergen of 30 kd. Methods: Allerg ens were separated and purified by high-performance liquid chromatogra phy with anion-exchange columns. The purity of the single proteins was checked by sodium dodecylsulfate-polyacrylamide gel electrophoresis, and their allergenicity was checked by immunoblotting with a pool of s era from patients allergic to kiwi. The allergens were characterized b y isoelectrofocusing and amino acid sequencing, and periodic acid-Schi ff stain was used to detect glycoproteins. Results: Proteins of 30, 28 , 24, and 17 kd were purified by high-performance liquid chromatograph y. IgE binding indicated the 30 kd protein, which shelved an isoelectr ic point of 3.5, as the major allergen of kiwi. Determination of its p artial amino acid sequence and comparison with the Swiss Protein Bank shelved that this was actinidin, the main protein component of kiwi. T he 24 and 28 kd proteins had the same N-terminal sequence, which did n ot correspond to any known protein. The 17 kd protein had a blocked N- terminal sequence. Conclusions: These results demonstrate that the maj or allergen of kiwi fruit, Act c 1, is actinidin, a proteolytic enzyme belonging to the class of thiol-proteases, Two other allergens of 24 and 28 kd appear identical on amino acid sequencing.