Abstract
Sunflower pollen was reported to contain respiratory allergens responsible for occupational allergy and pollinosis. The present study describes the comprehensive characterization of a major sunflower allergen Hel a 6. Natural Hel a 6 was purified from sunflower pollen by anion exchange and gel filtration chromatography. Hel a 6 reacted with IgE-antibodies from 57% of 39 sunflower-sensitized patient sera suggesting it to be a major allergen. The patients were of Indian origin and suffering from pollinosis and allergic rhinitis. Hel a 6 exhibited allergenic activity by stimulating mediator release from basophils. Monomeric Hel a 6 displayed pectate lyase activity. The effect of various physicochemical parameters such as temperature, pH, and calcium ion on the functional activity of Hel a 6 revealed a stable nature of the protein. Hel a 6 was folded, and its melting curve showed reversible denaturation in which it refolded back to its native conformation from a denatured state. Hel a 6 displayed a high degree of sequence conservation with the pectate lyase allergens from related taxonomic families such as Amb a 1 (67%) and Art v 6 (57%). The IgE-cross reactivity was observed between Hel a 6 and its ragweed and mugwort homologs. The cross-reactivity was further substantiated by the mediator release when Hel a 6-sensitized effector cells were cross-stimulated with Art v 6 and Amb a 1. Several putative B cell epitopes were predicted and mapped on these 3 allergens. Two antigenic regions were found to be commonly shared by these 3 allergens, which could be crucial for cross-reactivity. In conclusion, Hel a 6 serves as a candidate molecule for diagnosis and immunotherapy for weed allergy.
Highlights
The global prevalence of IgE-antibody mediated respiratory allergy caused by airborne pollen grains is increasing at an alarming rate
Advancement of recombinant DNA technology and genetic engineering has enabled the researchers to manufacture the allergy-eliciting components on a large scale to be used in the diagnostic antigen panel and to manipulate the allergen structure to create an attenuated version to be used for immunotherapy
The present study describes the comprehensive characterization of a new major allergen of sunflower pollen designated as Hel a 6, which is a pectate lyase
Summary
The global prevalence of IgE-antibody mediated respiratory allergy caused by airborne pollen grains is increasing at an alarming rate. The foremost part of this task is to identify, purify, and derive the sequence information of the natural allergen from its natural source Another member of the Asteraceae family is sunflower (Helianthus annuus), which grows all over the world and is commercially cultivated for edible oil. One of our earlier reports identified 8 novel allergens from sunflower pollen through a proteomic study and the major allergen being a pectate lyase, which displayed frequent IgE-reactivity within a population of pollinosis patients from an Indian megacity[8]. Most of these patients were reported to either work in the sunflower oil industry or to have sunflower plantations in their vicinity. We aimed to purify and characterize the sunflower allergen Hel a 6 (MW 42 kDa; pI 4.3) to estimate its potential as a candidate molecule for diagnosis and therapy
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