Identification and characterization of a basic thaumatin-like protein (TLP 2) as an allergen in sapodilla plum (Manilkara zapota)

Scope: Cases of oral allergy syndrome following the ingestion of sapodilla plum (Manilkara zapota) have been reported rarely. As the causative allergens are not known, the main objective of this study was to identify and characterize the important allergens in sapodilla. Methods and results: Allergy to sapodilla was diagnosed by case history, skin prick test, and serum allergen-specific IgE. The allergen was detected by IgE immunoblotting, purified on SP-Sepharose and characterized by native/SDS-PAGE, IEF, MS, and amino acid composition. Several cases of allergy to sapodilla fruit were identified; majority of the sapodilla-allergic subjects (6/7) experienced typical oral allergy syndrome symptoms, and allergen-specific IgE to the purified protein was positive. The allergen has a pI ≥9.5 and high contents of arginine, threonine, glycine, and cysteine. Circular dichroism revealed a secondary structure rich in beta sheets/turns. Based on its N-terminal sequence of A-T-F-D-I-Q-N-N-C-X-Y-, the allergen (21 578 Da) was identified as a thaumatin-like protein by homology. Conclusion: The causative allergen in sapodilla plum has been identified and characterized as a highly basic thaumatin-like protein belonging to the pathogenesis-related protein (PR-5) family, which has been recognized as a new family of conserved, cross-reactive plant allergens.