MOLECULAR-CLONING OF A MAJOR COCKROACH (BLATTELLA-GERMANICA) ALLERGEN, BLA-G-2 - SEQUENCE HOMOLOGY TO THE ASPARTIC PROTEASES

Inhalation of allergens produced by the German cockroach (Blattella ge rmanica) elicits IgE antibody formation and the development of asthma in genetically predisposed individuals. We compared the allergenic imp ortance of two cockroach (CR) allergens, Bla g 1 and Bla g 2, and dete rmined the complete amino acid sequence of the major 36-kDa allergen, Bla g 2. A survey of 106 sera from CR allergic patients showed the pre valence of IgE antibodies to Bla gl and Bla g 2 to be 30.2% and 57.6%, respectively. Immediate skin tests on 7 selected patients gave positi ve reactions using 10(-3) mu g/ml either allergen, whereas controls sh owed no response to 10 mu g/ml. Natural Bla g 2 was purified and the s equence of the NH2 terminus and tryptic peptides, comprising 36% of th e molecule, was determined. The cDNA for Bla g 2 was cloned from a B. germanica expression library and encoded a 24 amino acid signal peptid e and a 328-amino acid mature protein, which showed sequence homology to aspartic proteases. Bla g 2 showed the highest degree of identity t o mosquito (Aedes aegypti) lysosomal aspartic protease (30.8%), with s imilar identity to pepsin, cathepsins D and E, renin, and chymosin, Bl a g 2 mRNA and protein were detected in B, germanica, but not in Perip laneta americana, the other principal domiciliary CR species in the U. S. High concentrations of Bla g 2 were found in CR digestive organs ( esophagus, gut, and proventriculus). The results show that Ela g 2 is a major species-specific allergen of B. germanica and suggest that the allergen functions as a digestive enzyme in the cockroach.