Importance of conformation for the IgE reactivity of sarcoplasmic calcium-binding protein from the black tiger shrimp Penaeus monodon

Sarcoplasmic calcium-binding protein (SCP) is an EF-hand Ca2+-binding protein recently identified as a new crustacean allergen. Some EF-hand Ca2+-binding allergens, such as parvalbumin (fish allergen) and Bet v 4 (birch pollen allergen), have been shown to contain conformational-type IgE epitopes associated with the Ca2+-chelating. This study was performed to clarify the relationships between IgE reactivity and structure of the black tiger shrimp SCP. When analyzed by ELISA in the absence and presence of EGTA, the IgE reactivity of the black tiger shrimp SCP was found to be considerably reduced by Ca2+-depletion. Furthermore, circular dichroism spectral data showed a conformational difference between Ca2+-bound and Ca2+-depleted forms of the black tiger shrimp SCP. On the other hand, the synthetic 18 peptides spanning the entire amino acid sequence of the black tiger shrimp SCP were all assessed to have little IgE-binding ability by ELISA. Our results demonstrate that the IgE reactivity of the black tiger shrimp SCP is attributable mostly to conformational-type IgE epitopes, at least part of which is maintained by Ca2+-chelating.