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.

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Tropomyosin (Pen a 1) from brown shrimp, Penaeus aztecus, has been identified as the only major shrimp allergen. Since beef, pork and chicken are other tropo-myosin-containing foods that are not very allergenic, tropomyosins can serve to investigate the contribution of the structural properties of a protein to its allergenicity. The aim of this study was to determine the primary structure of Pen a 1 and to identify IgE-binding epitopes. The screening of a unidirectional expression cDNA library from shrimp tail muscle with the Pen-a-1-specific monoclonal antibody 4.9.5 resulted in 4 positive Escherichia coli clones. Immunoblot analysis with human sera from shrimp-allergic subjects demonstrated IgE binding of all 4 recombinant shrimp proteins. Three of 4 expressed recombinant proteins have a molecular weight of approximately 36 kD, consistent with the molecular weight of natural Pen a 1. The DNA sequence analysis identified these recombinant shrimp proteins as tropomyosin and could be aligned with the sequence of greasyback shrimp (Metapenaeus ensis) tropomyosin (Met e 1). In order to characterize contiguous IgE-binding epitopes of Pen a 1, a peptide library (Novagen epitope mapping system) expressing 10–30 amino-acid-residue-long recombinant Pen a 1 peptides was constructed and screened with human IgE. Four recombinant, IgE-reactive Pen a 1 peptides were selected and sequenced. They show various degrees of sequence identity with tropomyosins of other arthropods, such as fruitfly and house dust mite, helminths and vertebrates.