Characterization and phylogenetic analysis of allergenic Tryp_alpha_amyl protein family in plants

Most known allergenic proteins in rice ( Oryza sativa ) seed belong to the Tryp_alpha_amyl family (PF00234), but the sequence characterization and the evolution of the allergenic Tryp_alpha_amyl family members in plants have not been fully investigated. In this study, two specific motifs were found besides the common alpha-amylase inhibitors (AAI) domain from the allergenic Tryp_alpha_amyl family members in rice seeds (trRSAs). To understand the evolution and functional importance of the Tryp_alpha_amy1 family and the specific motifs for the allergenic one, a BLAST search identified 75 homologous proteins of trRSAs (trHAs) from 22 plant species including main crops such as rice, maize ( Zea mays ), wheat ( Triticum aestivum ), and sorghum ( Sorghum bicolor ) from all available sequences in the public databases. Statistical analysis showed that the allergenicity of trHAs is closely associated with these two motifs with high number of cysteine residues (p value = 0.00026), and the trHAs with and without the two motifs were clustered into separate clades, respectively. Furthermore, significant difference was observed on the secondary and tertiary structures of allergenic and nonallergenic trHAs. In addition, expression analysis showed that trHA-encoding genes of purple false brome ( Brachypodium distachyon ), barrel medic ( Medicago truncatula ), rice, and sorghum are dominantly expressed in seeds. This work provides insight into the understanding of the properties of allergens in the Tryp_alpha_amyl family and is helpful for allergy therapy.