title: Molecular and immunological characterization of the glycosylated orange allergen Cit s 1.
abstract: The IgE of sera from patients with a history of allergy to oranges (Citrus sinensis) binds a number of proteins in orange extract, including Cit s 1, a germin-like protein. In the present study, we have analyzed its immunological cross-reactivity and its molecular nature. Sera from many of the patients examined recognize a range of glycoproteins and neoglycoconjugates containing beta1,2-xylose and core alpha1,3-fucose on their N-glycans. These reagents also inhibited the interaction of Cit s 1 with patients' sera, thus underlining the critical role of glycosylation in the recognition of this protein by patients' IgE and extending previous data showing that deglycosylated Cit s 1 does not possess IgE epitopes. In parallel, we examined the peptide sequence and glycan structure of Cit s 1, using mass spectrometric techniques. Indeed, we achieved complete sequence coverage of the mature protein compared with the translation of an expressed sequence tag cDNA clone and demonstrated that the single N-glycosylation site of this protein carries oligosaccharides with xylose and fucose residues. Owing to the presumed requirement for multivalency for in vivo allergenicity, our molecular data showing that Cit s 1 is monovalent as regards glycosylation and that the single N-glycan is the target of the IgE response to this protein explain the immunological cross-reactive properties of Cit s 1 as well as its equivocal nature as a clinically relevant allergen.
authors.affiliation: Department für Chemie, Universität für Bodenkultur, Muthgasse 18, A-1190 Wien, Austria.
authors.forename: Gerald
authors.initials: G
authors.lastname: Pöltl
authors.forename: Oussama
authors.initials: O
authors.lastname: Ahrazem
authors.forename: Katharina
authors.initials: K
authors.lastname: Paschinger
authors.forename: M Dolores
authors.initials: MD
authors.lastname: Ibañez
authors.forename: Gabriel
authors.initials: G
authors.lastname: Salcedo
authors.forename: Iain B H
authors.initials: IB
authors.lastname: Wilson
mesh_terms: D000485:Allergens / Q000737:chemistry* / Q000276:immunology*; D000595:Amino Acid Sequence; D032084:Citrus sinensis / Q000276:immunology*; D003429:Cross Reactions; D004797:Enzyme-Linked Immunosorbent Assay; D005643:Fucose / Q000032:analysis; D006023:Glycoproteins / Q000737:chemistry* / Q000276:immunology*; D006031:Glycosylation; D006801:Humans; D007106:Immune Sera / Q000276:immunology; D007073:Immunoglobulin E / Q000097:blood; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010446:Peptide Fragments / Q000737:chemistry; D010940:Plant Proteins / Q000737:chemistry* / Q000276:immunology*; D011134:Polysaccharides / Q000737:chemistry / Q000276:immunology; D020539:Sequence Analysis, Protein; D014357:Trypsin / Q000737:chemistry; D014994:Xylose / Q000032:analysis
chemical_list: D000485:Allergens; D006023:Glycoproteins; D007106:Immune Sera; D010446:Peptide Fragments; D010940:Plant Proteins; D011134:Polysaccharides; D005643:Fucose; D007073:Immunoglobulin E; D014994:Xylose; D014357:Trypsin