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

J Allergy Clin Immunol. 2006 Jun;117(6):1389-95. doi: 10.1016/j.jaci.2006.02.017. Epub 2006 May 2.

Abstract

Background: The known cockroach allergens do not appear to account for the full repertoire of IgE responses.

Objective: To identify and investigate the importance of other Blattella germanica allergens contributing to cockroach allergy.

Methods: 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.

Results: 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-(beta-aminoethylether)-N,N,N',N'-tetraacetic acid did not significantly affect IgE binding in most cases. Interestingly, addition of 10 mmol/L CaCl2 after calcium depletion increased IgE binding by approximately 2-fold, a finding not previously reported for calcium binding allergens.

Conclusion: Bla g 6 is a troponin allergen with a calcium dependent IgE reactivity that may be involved in muscle contraction.

Clinical implications: Bla g 6 homologous allergens may occur among other insects and cause cosensitization or allergenic cross-reactivity.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Allergens / biosynthesis
  • Allergens / chemistry
  • Allergens / genetics
  • Allergens / immunology*
  • Allergens / metabolism
  • Amino Acid Sequence
  • Animals
  • Antigens, Plant
  • Calcium / metabolism*
  • Calcium / physiology
  • Cockroaches / immunology*
  • Humans
  • Immunoglobulin E / metabolism*
  • Insect Proteins / biosynthesis
  • Insect Proteins / immunology*
  • Insect Proteins / metabolism
  • Molecular Sequence Data
  • Periplaneta / immunology
  • Protein Binding / immunology
  • Protein Isoforms / biosynthesis
  • Protein Isoforms / immunology
  • Protein Isoforms / metabolism
  • Sequence Homology, Amino Acid
  • Troponin C / biosynthesis
  • Troponin C / immunology*
  • Troponin C / metabolism

Substances

  • Allergens
  • Antigens, Plant
  • Bla g 6 allergen, Blattella germanica
  • Insect Proteins
  • Per a 6 allergen, Periplaneta americana
  • Protein Isoforms
  • Troponin C
  • Immunoglobulin E
  • Calcium

Associated data

  • GENBANK/AY792950
  • GENBANK/DQ279092
  • GENBANK/DQ279093
  • GENBANK/DQ279094