β(1,2)-Xylose and α(1,3)-Fucose Residues Have a Strong Contribution in IgE Binding to Plant Glycoallergens

Abstract

Primary structures of the N-glycans of two major pollen allergens (Lol p 11 and Ole e 1) and a major peanut allergen (Ara h 1) were determined. Ole e 1 and Ara h 1 carried high mannose and complex N-glycans, whereas Lol p 11 carried only the complex. The complex structures all had a ␤(1,2)-xylose linked to the core mannose. Substitution of the proximal N-acetylglucosamine with an ␣(1,3)-fucose was observed on Lol p 11 and a minor fraction of Ole e 1 but not on Ara h 1. To elucidate the structural basis for IgE recognition of plant N-glycans, radioallergosorbent test analysis with protease digests of the three allergens and a panel of glycoproteins with known N-glycan structures was performed. It was demonstrated that both ␣(1,3)-fucose and ␤(1,2)-xylose are involved in IgE binding. Surprisingly, xylose-specific IgE antibodies that bound to Lol p 11 and bromelain did not recognize closely related xylose-containing structures on horseradish peroxidase, phytohemeagglutinin, Ole e 1, and Ara h 1. On Lol p 11 and bromelain, the core ␤-mannose is substituted with just an ␣(1,6)-mannose. On the other xylose-containing N-glycans, an additional ␣(1,3)-mannose is present. These observations indicate that IgE binding to xylose is sterically hampered by the presence of an ␣(1,3)-antenna.In the early 1980s, it was reported for the first time that IgE antibodies in sera of pollen allergic patients can be directed to carbohydrate determinants on glycoproteins (1-3). The carbohydrate nature of these epitopes was supported by several characteristic properties, such as their periodate sensitivity and their resistance to heating and protease digestion. IgE antibodies directed to these carbohydrate structures were shown to be extremely cross-reactive not only between different plant-derived glycoproteins but also to glycoproteins from invertebrate animals (e.g. seafood and insect venoms) (2, 4 -7).This high degree of cross-reactivity was explained by the conserved structure of N-glycans from plants and invertebrate animals, sharing several features that are not found in mammalian N-glycans (8). More recently, several research groups have confirmed the role of carbohydrate epitopes in IgE reactivity (9 -22).In plants, the N-glycosylation of proteins starts by the transfer of the oligosaccharide precursor Glc 3 Man 9 GlcNAc 2 in the endoplasmic reticulum (reviewed in Ref. 23). This structure can subsequently be modified by glycosidases and glycosyltransferases during transport of the glycoprotein through the endoplasmic reticulum, the Golgi apparatus, and the vacuole. Depending on the accessibility of the glycan side chain, these enzymes can convert the precursor to high mannose-type Nglycans ranging from Man 9 GlcNAc 2 to Man 5 GlcNAc 2 and then to complex-type N-glycans having an ␣(1,3)-fucose attached to the proximal glucosamine residue and/or a ␤(1,2)-xylose residue attached to the ␤-mannose. These linkages of fucose and xylose are typical for complex N-glycans from plants and invertebrate animals and are not found in mammals. Mo...

Reduced Immunogenicity of Arabidopsis hgl1 Mutant N-Glycans Caused by Altered Accessibility of Xylose and core Fucose Epitopes

“…Earlier reports showed that xylose is not always bound equally well by specific antibodies (31), and one study suggested that presence of ␣1,3-mannose on M3X(F) structures might interfere sterically with binding (20). In our study, three-dimensional-glycan modeling provided a first correlative and plausible explanation for altered xylose recognition.…”

“…Previously, van Ree et al (20) concluded that xylose-specific IgE antibodies that bound to bromelain M2XF (MUXF) N-glycan did not recognize closely related M3XF (MMXF) structures of PHA-L or HRP because of sterical hindrance caused by the presence of ␣1,3-mannose in case of M3XF (MMXF), whereas Bencúrová et al (31) concluded that bromelain is not useful for detection of xylose-specific antibodies because of an absence of ␣1,3-mannose from M2X (MUX).…”

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.…”

Structural characterization of the N-glycans of gpMuc from Mucuna pruriens seeds

“…This is in line with recent literature on crossreactive carbohydrate determinants. The (α1-3)-fucosylated and (β1-2)-xylosylated N-glycans have been repeatedly reported to be immunogenic in mammals [12][13][14][15][16][17] and in fact (β1-2)-linked Xyl and (α1-3)-linked Fuc residues have been identified as the epitope structures for IgE binding [18,19] in patients allergic to tree and grass pollens. The vast potential for cross-reaction of antibodies with one or both of these carbohydrate determinants is further extended by the Table 5 Survey of N-glycans obtained from gpMuc, together with their relative amounts occurrence of the same epitope structures on glycoproteins of insects, molluscs and parasitic worms [20][21][22].…”