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J Allergy Clin Immunol. 2006 Jun;117(6):1389-95. Epub 2006 May 2.

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

Author information

1
School of Biosciences, Cardiff University, VA 22903, USA.

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.

PMID:
16751002
DOI:
10.1016/j.jaci.2006.02.017
[Indexed for MEDLINE]

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