Abstract
Cockroaches produce potent allergens that are an important cause of asthma. The two principal domiciliary cockroach species, Blattella germanica and Periplaneta americana, secrete major allergens, Bla g 1 and Per a 1. Here, we report the molecular cloning of three Bla g 1 cDNA clones, which showed 70% amino acid sequence identity with Per a 1. Plaque immunoassays with human IgE antibodies or murine monoclonal antibodies showed that these allergens were antigenically cross-reactive. The Bla g 1 sequences also showed homology to five previously undefined cockroach allergen sequences. An unusual feature of all these sequences was that they contained multiple tandem amino acid repeats of approximately 100 amino acid residues. Between one and seven repeat units were identified by dot-plot matrix analysis. The sequences also showed homology to a mosquito protein involved in digestion (ANG12 precursor) and to mitochondrial energy transfer proteins. High levels of Bla g 1 were found in cockroach hindgut and proventriculus. Amino acid sequencing of natural Bla g 1 and Per a 1 suggested that these allergens are cleaved by trypsin-like enzymes following secretion into the digestive tract. The repeat sequences appear to have evolved by duplication of an ancestral amino acid domain, which may have arisen from the mitochondrial energy transfer proteins.
Highlights
Inhalation of environmental allergens from pollens, mites, animal danders, insects, and fungi induces IgE antibody responses in ϳ20% of the Western population
Previous studies established that Bla g 1 and Per a 1 are important allergens that elicit IgE Ab responses in ϳ50% of cockroach allergic patients
The three Bla g 1 cDNA clones encode the sequences of two isoallergens, Bla g 1.01 and Bla g 1.02, with 75% amino acid sequence identity
Summary
Antibody; mAb, monoclonal antibody; BCIP, 5-bromo-4-chloro-3-indolyl phosphate; ELISA, enzymelinked immunosorbent assay; ER, endoplasmic reticulum. Structural studies, and assays of biological function have shown that allergens are a diverse group of proteins, including enzymes, ligand binding proteins, and structural and regulatory proteins [2, 3]. Several allergens have been cloned from German cockroach (Blattella germanica), including Bla g 2 (aspartic protease); Bla g 4 (lipocalin); and Bla g 5 (glutathione transferase) (9 –11). These allergens elicit IgE Ab responses in 50 – 80% of cockroach allergic patients and are B. germanica-specific [12]. Cross-reactive allergens have been identified in both German and American cockroach (Bla g 1 and Per a 1) but their structure was unknown [13,14,15]. The allergens show sequence homology to a mosquito protein associated with digestive function (ANG12 precursor), and the repeat sequences may have evolved from ancestral amino acid domains found in mitochondrial energy transfer proteins
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