Role of complex asparagine-linked glycans in the allergenicity of plant glycoproteins

Abstract

Many plant proteins, particularly those found in foods and pollen, are known to act as sensitizing agents in humans upon repeated exposure. Among the cereal flour proteins involved in asthmatic reactions, those members of the alpha-amylase inhibitor family which are glycosylated, polypeptides, BMAI-1, BTAI-CMb*, and WTAI-CM16* are particularly reactive both in vivo and in vitro. We show here that these major glycoprotein allergens carry a single asparagine-linked complex glycan that contains both beta 1-->2 xylose and alpha 1-->3 fucose. Evidence is presented that the xylosyl residue and, to a lesser extent, the fucosyl residue are key IgE-binding epitopes and largely responsible for the allergenicity of these and unrelated proteins from plants and insects. Our results suggest that the involvement of xylose- and fucose-containing complex glycans in allergenic responses may have been underestimated previously; these glycans provide a structural basis to help explain the cross-reactivities often observed between pollen, vegetable food, and insect allergens.

Structural requirements for Arabidopsisβ1,2‐xylosyltransferase activity and targeting to the Golgi

“…Particularly, the plant Nglycan core is often substituted by 1,2-linked xylose (Xyl) and 1,3-linked fucose (Fuc) residues not found in their mammalian counterparts. These residues are components of carbohydrate epitopes responsible for the immunogenicity and/or allergenicity of plant N-glycans in most mammals (Faye et al, 1993;Garcia-Casado et al, 1996;Wilson and Altmann, 1998;Van Ree et al, 2000). The N-glycan maturation machinery is relatively well known in mammals and about one hundred mammalian Golgi glycosyltransferases have been cloned and sequenced.…”

N-Glycosylation of the 66-kDa Cell-Wall Glycoprotein of a Red Microalga

“…These xylose residues are attached to a different monosaccharide (and in a different linkage position) than known glycans. Therefore, it is not known whether the xylose residues reported here have allergenic natures similar to those of the xylose residues found in other known glycans [87][88]. In addition, we also do not know how the additional methyl groups affect the protein and its immunogenic response.…”

Unique N-Glycan Moieties of the 66-kDa Cell Wall Glycoprotein from the Red Microalga Porphyridium sp.

“…These findings indicate the existence of special glycosyltransferases and glycosylation pathways, unique to the red microalgae. It is not known whether the Xyl residues reported here have a similar allergenic nature to the Xyl residues found in other glycans (26,29). The glycosylation pattern might be important when using the red microalgae as cell factories for biopharmaceuticals.…”