Pollen allergens are restricted to few protein families and show distinct patterns of species distribution

Abstract

Background: Inhalative allergies are elicited predominantly by pollen of various plant species. However, a classification of the large number of identified pollen allergens is still missing.

Objective: To analyze pollen allergen sequences with respect to protein family membership, taxonomic distribution of protein families, and interspecies variability.

Methods: Protein family memberships of all plant allergen sequences from the Allergome database were determined by using the Protein Families Database of Alignments and Hidden Markov Models. The taxonomic distribution of pollen allergens was established from the Integrated Taxonomic Information System. Members of abundant pollen allergen families were compared with allergenic and nonallergenic homologues by database similarity searches and multiple sequence alignments.

Results: Pollen allergens were classified into 29 of 7868 protein families. Expansins, profilins, and calcium-binding proteins constitute the major pollen allergen families, whereas most plant food allergens belong to the prolamin, cupin, or profilin families. Pollen allergens were revealed to be ubiquitous (eg, profilins), present in certain plant families (eg, pectate lyases), or limited to a single taxon (eg, thaumatin-like proteins). Allergenic plant profilins constitute a highly conserved family with sequence identities of 70% to 85% among each other but low identities of 30% to 40% with nonallergenic profilins from other eukaryotes, including human beings. Similarly, allergenic polcalcins possess sequence identities of 64% to 92% but show low identities of 39% to 42% to related nonallergenic calmodulins and calmodulin-like proteins from vegetative plant tissues and man.

Conclusion: This classification of pollen allergens into protein families will aid in predicting cross-reactivity, designing comprehensive diagnostic devices, and assessing the allergenic potential of novel proteins.