Molecular identification of the lobster muscle protein tropomyosin as a seafood allergen

Crustaceans are a major cause of seafood allergy. Recent studies have identified tropomyosin as the major allergen in shrimp. However, such data are lacking in other crustaceans. In the present study lobster allergens were identified and characterized by molecular cloning, sequencing, and expression. An IgE-reactive complementary DNA clone of 2 kilobase pairs (kb) was identified by screening an expression library of the spiny lobster Panulirus stimpsoni using sera from subjects with crustacean allergy. Expression and sequencing of this clone showed that it has an opening reading frame of 274 amino acids, coding for a 34-kDa protein designated as Pan s I. In addition, we expressed the fast muscle tropomyosin from the American lobster Homarus americanus and found that this protein, coined Horn a I, was also recognized by IgE from patients with crustacean allergies. The deduced amino acid sequences of Pan s I and Hom a I, which are the first identified lobster allergens, show significant homology to shrimp tropomyosin. Sera from subjects with crustacean allergies, when pre-absorbed with recombinant proteins Pan s I or Hom a I, lost their IgE reactivity to muscle extract of P. stimpsoni and H. americanus. Preincubation of crustacean allergy sera with the recombinant shrimp tropomyosin Met e I also removed their IgE reactivity to lobster muscle extracts. The results suggest that patients with allergic reactions to crustaceans have common and possibly cross-reactive IgE-reactive epitopes in lobster and shrimp.