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16?Pollen Allergens Differ From Nonallergenic Pollen Proteins by Their Lower Extent of Evolutionary Conservation.

ABSTRACT: BackgroundPollen contains hundreds of different proteins. However, only a small fraction of them have been identified to be allergenic. We aimed to test the hypothesis that most pollen proteins are non-allergenic due to their high extent of sequence conservation among non-related species.MethodsData on the composition of pollen proteomes of birch (Betula pendula), pellitory (Parientaria judaica) and timothy grass (Phleum pratense) were obtained from the literature. Sequences were downloaded from UniProt and manually classified into allergens and non-allergens. Complete proteome sequences of 3 dicotyledonous species (Arabidopsis thaliana, Populus trichocarpa and Vitis vinifera), 2 monocotyledons (Oryza sativa subsp. japonica and Zea mays) and one moss (Physcomitrella patents) were downloaded from ENSEMBL Plants. Sequences of pollen proteins were compared to these proteomes by using BLAST and the hits yielding the highest sequence identity recorded taking into account only sequence alignments at least 40 residues in length. The distributions of maximum sequence identities of allergens and non-allergens from each species were compared using the Mann-Whitney test.ResultsAllergens from birch and pellitory pollen were significantly (P < 0.001) less similar to proteins from monocots than non-allergenic pollen proteins. Median sequence identities to the nearest rice and maize homologues were 49 and 52% for birch allergens, 86 and 85% for birch non-allergens, 37 and 37% for pellitory allergens, and 87 and 89% for pellitory non-allergens. Similarly, timothy grass pollen allergens were significantly (P < 0.0001) less similar to dicot proteins than non-allergenic pollen proteins. Median sequence identities to the nearest homologues were 43 to 44% for allergens and 81 to 83% for non-allergens. A comparison of all 3 pollen proteomes to sequences from the moss P. patens yielded similarly significant differences.ConclusionsPollen allergens belong to evolutionary less conserved protein families than non-allergenic pollen proteins. The continual exposure of the human immune system to nearly identical and hence highly cross-reactive conserved proteins from multiple pollen and plant food species most likely leads to the induction of immunological tolerance rather than allergic sensitization.

SUBMITTER: Radauer C

PROVIDER: S-EPMC3512598 | biostudies-other | 2012 Feb

REPOSITORIES: biostudies-other

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Project description:Comparative genomics have facilitated the mining of biological information from a genome sequence, through the detection of similarities and differences with genomes of closely or more distantly related species. By using such comparative approaches, knowledge can be transferred from the model to non-model organisms and insights can be gained in the structural and evolutionary patterns of specific genes. In the absence of sequenced genomes for allergenic grasses, this study was aimed at understanding the structure, organisation and expression profiles of grass pollen allergens using the genomic data from Brachypodium distachyon as it is phylogenetically related to the allergenic grasses. Combining genomic data with the anther RNA-Seq dataset revealed 24 pollen allergen genes belonging to eight allergen groups mapping on the five chromosomes in B. distachyon. High levels of anther-specific expression profiles were observed for the 24 identified putative allergen-encoding genes in Brachypodium. The genomic evidence suggests that gene encoding the group 5 allergen, the most potent trigger of hay fever and allergic asthma originated as a pollen specific orphan gene in a common grass ancestor of Brachypodium and Triticiae clades. Gene structure analysis showed that the putative allergen-encoding genes in Brachypodium either lack or contain reduced number of introns. Promoter analysis of the identified Brachypodium genes revealed the presence of specific cis-regulatory sequences likely responsible for high anther/pollen-specific expression. With the identification of putative allergen-encoding genes in Brachypodium, this study has also described some important plant gene families (e.g. expansin superfamily, EF-Hand family, profilins etc) for the first time in the model plant Brachypodium. Altogether, the present study provides new insights into structural characterization and evolution of pollen allergens and will further serve as a base for their functional characterization in related grass species.

Project description:BackgroundPollen released by allergenic members of the botanically unrelated families of Asteraceae and Cupressaceae represent potent elicitors of respiratory allergies in regions where these plants are present. As main allergen sources the Asteraceae species ragweed and mugwort, as well as the Cupressaceae species, cypress, mountain cedar, and Japanese cedar have been identified. The major allergens of all species belong to the pectate lyase enzyme family. Thus, we thought to investigate cross-reactivity pattern as well as sensitization capacities of pectate lyase pollen allergens in cohorts from distinct geographic regions.MethodsThe clinically relevant pectate lyase pollen allergens Amb a 1, Art v 6, Cup a 1, Jun a 1, and Cry j 1 were purified from aqueous pollen extracts, and patients' sensitization pattern of cohorts from Austria, Canada, Italy, and Japan were determined by IgE ELISA and cross-inhibition experiments. Moreover, we performed microarray experiments and established a mouse model of sensitization.ResultsIn ELISA and ELISA inhibition experiments specific sensitization pattern were discovered for each geographic region, which reflected the natural allergen exposure of the patients. We found significant cross-reactivity within Asteraceae and Cupressaceae pectate lyase pollen allergens, which was however limited between the orders. Animal experiments showed that immunization with Asteraceae allergens mainly induced antibodies reactive within the order, the same was observed for the Cupressaceae allergens. Cross-reactivity between orders was minimal. Moreover, Amb a 1, Art v 6, and Cry j 1 showed in general higher immunogenicity.ConclusionWe could cluster pectate lyase allergens in four categories, Amb a 1, Art v 6, Cup a 1/Jun a 1, and Cry j 1, respectively, at which each category has the potential to sensitize predisposed individuals. The sensitization pattern of different cohorts correlated with pollen exposure, which should be considered for future allergy diagnosis and therapy.

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16?Pollen Allergens Differ From Nonallergenic Pollen Proteins by Their Lower Extent of Evolutionary Conservation.

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