Are defensins important plant allergens?

Defensins are small disulfide-rich proteins, which are widely distributed in plants. They all have a knottin domain with an abcabc topology, which is characterized by the existence of a knot interlaced with disulfide bridges. The knot is made up of a disulphide bridge, which is crossed by a loop formed by two other disulfide bridges-connected to a peptide backbone. This structure denotes that the crossing disulfide bridge(s) is oriented perpendicularly to the two other disulfide bridges forming the loop. The knottin domain can be connected either by a long C-terminal tail rich in hydroxyproline (definsins with a long chain with about 110 amino acids) or by a short C-terminal chain (with about 50 amino acids). The Art v 1 allergen of mugwort (Artemisia vulgaris) pollen is the prototype of the long-chain defensins whereas defensins of the Brassicaceae essentially belong to the short-chain defensin group. Except for Art v 1 and the closely-related Amb a 4 allergen from ragweed (Ambrosia artemisiifolia) pollen, both of which are well-known allergens, the allergenicity of other plant defensins is far from being clinically demonstrated. Nevertheless, the fact that electropositive amino acid patches (with lysine and arginine) and electronegative patches (with aspartic and glutamic acids) which have been identified on the surface of both Art v 1 and Amb a 4 also exist in a few other defensins suggests that other defensins could also be allergenic. Further clinical and immunological investigations are necessary to ascertain the allergenicity of these putative defensin allergens. (C) 2013 Elsevier Masson SAS. All rights reserved.