Oil bodies (oleosomes): Occurrence, structure, allergenicity

Oil bodies, or oleosomes, consist of lipid droplets confined within a protein-containing lipid monolayer that are widely distributed in oil seeds, particularly edible oil seeds. Amphiphilic proteins embedded in the lipid monolayer form an interface between the hydrophobic core of the oil bodies and the hydrophilic cytoplasm in which these organelles are distributed. They also play a crucial role in stabilizing oil bodies and preventing their coalescence via charge and steric hindrances. Oleosins, small proteins measuring 16-25 kDa, are the most abundant amphiphilic proteins occurring in the lipid monolayer surrounding the triglyceride core of oil bodies. They are composed of a hydrophobic alpha-helical hairpin anchored to the lipid monolayer and extended on both the N- and C-terminal ends by hydrophilic alpha-helical arms lying on the surface of the lipid monolayer in contact with the cytoplasm. Oleosins from peanut (Ara h 10, Ara h 11, Ara h 14, Arab 15), hazelnut (Cor a 12, Cor a 13) and sesame (Ses i 4, Ses i 5) have been identified as major lipophilic IgE-binding allergens that are often associated with severe allergic reactions in sensitized subjects. Their allergenicity depends on the occurrence of IgE-binding epitopes along the hydrophilic arms attached to the hydrophobic alpha-helical hairpin. In addition, the phylogenetic relationships observed between oleosins belonging to different edible oil seeds suggest that some IgE-binding cross-reactivity may occur between oleosins of different origins. However, due to their lipophilic character, they are underrepresented in the water-soluble allergen extracts used in diagnosing food allergies and their role in triggering allergic responses in peanut and other tree nut allergies is thus doubtless greatly underestimated. (C) 2018 Elsevier Masson SAS. All rights reserved.