Identification of the Major Brown Shrimp (Penaeus aztecus) Allergen as the Muscle Protein Tropomyosin

Shrimp, a major seafood allergen, was investigated as a model food allergen. Extracts from both shrimp (Penaeus aztecus) meat and cooking fluid contain a substantial and similar amount of allergenic activity. A 36-kD allergen, demonstrated in both extracts by SDS-PAGE/Western blot analysis, reacted with 28/34 (82%) sera from shrimp-sensitive, skin test and RAST-positive, individuals. This allergen, named Pen a I, was isolated by SDS-PAGE; its amino acid composition was rich in aspartic and glutamic acids. A 21-residue peptide, obtained from endoproteinase Lys-C digested Pen a I by high-performance liquid chromatography, demonstrated significant homology (60-87%) with the muscle protein tropomyosin from various species and origins. The greatest homology (87%) was noted with tropomyosin of the fruit fly (Drosophila melanogaster) reflecting the phylogenic relationship between these two arthropods. These studies demonstrate that tropomyosin is the major shrimp allergen. Although the amino acid sequence of this shrimp muscle protein shares considerable homology with tropomyosins of other species including man, significant differences remain in allergenic activity.