The novel structure of the cockroach allergen Bla g 1 has implications for allergenicity and exposure assessment

Abstract

Background Sensitization to cockroach allergens is a major risk factor for asthma. The cockroach allergen Bla g 1 has multiple repeats of ~100 amino acids, but the fold of the protein and the biological function are unknown. Objective To determine the structure of Bla g 1, investigate the implications for allergic disease, and standardize cockroach exposure assays. Methods Natural Bla g 1 and recombinant constructs were compared by ELISA using specific murine IgG and human IgE. The structure of Bla g 1 was determined by X-ray crystallography. Mass spectrometry and NMR were utilized to examine ligand-binding properties of the allergen. Results The structure of a recombinant Bla g 1 construct with comparable IgE and IgG reactivity to the natural allergen was solved by X-ray crystallography. The Bla g 1 repeat forms a novel fold with 6 helices. Two repeats encapsulate a large and nearly spherical hydrophobic cavity, defining the basic structural unit. Lipids in the cavity varied depending on the allergen origin. Palmitic, oleic and stearic acids were associated with nBla g 1 from cockroach frass. One Unit of Bla g 1 was equivalent to 104 ng of allergen. Conclusions Bla g 1 has a novel fold with a capacity to bind various lipids, which suggests a digestive function associated with non-specific transport of lipid molecules in cockroaches. Defining the basic structural unit of Bla g 1 facilitates the standardization of assays in absolute units for the assessment of environmental allergen exposure.

The genes and the environment in nasal allergy

“…Strategies for protecting workers are limited to monitoring, understanding how occupational exposures occur, and adopting measures to decrease allergen exposure [26]. Lastly, recent work in this field includes molecular characterization of allergens and their epitopes [27,28], which may lead to development of future diagnostic and prognostic tests for specific allergen epitopes, the socalled component testing, which is already used now in food allergy.…”

Characterization of an anti-Bla g 1 scFv: Epitope mapping and cross-reactivity

“…Whereas Bla g 2 is a stable globular protein, Bla g 1 is a more complex allergen, and has a fragmentation pattern on SDS-PAGE that made standardization difficult for a long time. It was only recently that 1 Unit of the allergen Bla g 1 was standardized to be 104 ng (Mueller et al, 2013). This will facilitate a better comparison of allergen exposure levels.…”

“…In other insect species, up to 7 copies of α and β are present on a single polypeptide chain (Randall et al, 2013). The two core sequences each form a pentagon of alpha helices with a sixth helix displaced above the plane of the pentagon (Mueller et al, 2013). The two pentagons of α and β interact via the rim, creating a large internal hydrophobic cavity that can bind various lipids (Mueller et al, 2013).…”

“…The two core sequences each form a pentagon of alpha helices with a sixth helix displaced above the plane of the pentagon (Mueller et al, 2013). The two pentagons of α and β interact via the rim, creating a large internal hydrophobic cavity that can bind various lipids (Mueller et al, 2013). The unstructured loops between α and β are frequently proteolyzed, leading to the mistaken impression on SDS-PAGE analysis that the protein is highly fragmented and therefore there is a consequent loss of antibody epitopes.…”

“…The unstructured loops between α and β are frequently proteolyzed, leading to the mistaken impression on SDS-PAGE analysis that the protein is highly fragmented and therefore there is a consequent loss of antibody epitopes. It has been demonstrated that even with variable fragmentation patterns, antibody recognition of the allergen was consistent, indicating that the core structure remains intact (Mueller et al, 2013). …”