Bla g 6: A troponin C allergen from Blattella germanica with IgE binding calcium dependence

• Published in: Journal of Allergy and Clinical Immunology 2006-06, Vol.117 (6), p.1389-1395
• Main Authors: Hindley, James, Wünschmann, Sabina, Satinover, Shama M., Woodfolk, Judith A., Chew, Fook Tim, Chapman, Martin D., Pomés, Anna
• Format: Article
• Language: English
• Subjects: allergens; Allergens - biosynthesis; Allergens - chemistry; Allergens - genetics; Allergens - immunology; Allergens - metabolism; Allergies; allergy; Amino Acid Sequence; Animals; Antigens, Plant; Asthma; Biological and medical sciences; Blattella germanica; Calcium - metabolism; Calcium - physiology; calcium binding proteins; Chromatography; Cloning; cockroach; Cockroaches - immunology; Dependence; Fundamental and applied biological sciences. Psychology; Fundamental immunology; Humans; Immunoassay; Immunoglobulin E - metabolism; Immunopathology; Insect Proteins - biosynthesis; Insect Proteins - immunology; Insect Proteins - metabolism; Medical sciences; Molecular Sequence Data; multiplex array technology; Periplaneta - immunology; Pichia pastoris; Protein Binding - immunology; Protein Isoforms - biosynthesis; Protein Isoforms - immunology; Protein Isoforms - metabolism; Sequence Homology, Amino Acid; Studies; Troponin C - biosynthesis; Troponin C - immunology; Troponin C - metabolism
• ISSN: 0091-6749; 1097-6825; 1365-2567
• DOI: 10.1016/j.jaci.2006.02.017

The known cockroach allergens do not appear to account for the full repertoire of IgE responses. To identify and investigate the importance of other Blattella germanica allergens contributing to cockroach allergy. A B germanica cDNA library was screened with pooled sera from patients with cockroach allergy. Three isoallergens of troponin C (Bla g 6) were cloned and expressed in Pichia pastoris. Homology modeling was performed by using Swiss-Model. IgE responses to purified allergens were simultaneously measured in 104 sera by using a fluorescent multiplex array system. The effect of calcium on IgE binding was investigated by ELISA. Three isoallergens, Bla g 6.0101, Bla g 6.0201, and Bla g 6.0301, were identified which share homology with insect troponin Cs and vertebrate calmodulins (61% to 78% and 42% to 44% amino acid identity, respectively) and have 2 EF-hand calcium binding domains. Molecular models of Bla g 6 showed 2 structurally homologous lobes connected by a linker that confers flexibility to the allergen. The prevalence of IgE binding to recombinant Bla g 6 was 14%. Calcium depletion by 10 mmol/L ethyleneglycol-bis-(β-aminoethylether)-N,N,N′,N′-tetraacetic acid did not significantly affect IgE binding in most cases. Interestingly, addition of 10 mmol/L CaCl 2 after calcium depletion increased IgE binding by approximately 2-fold, a finding not previously reported for calcium binding allergens. Bla g 6 is a troponin allergen with a calcium dependent IgE reactivity that may be involved in muscle contraction. Bla g 6 homologous allergens may occur among other insects and cause cosensitization or allergenic cross-reactivity.