Glycobiology Advance Access originally published online on November 9, 2006
Glycobiology 2007 17(2):220-230; doi:10.1093/glycob/cwl068
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Molecular and immunological characterization of the glycosylated orange allergen Cit s 1
2 Department für Chemie, Universität für Bodenkultur, Muthgasse 18, A-1190 Wien, Austria
3 Unidad de Bioquímica, Departamento de Biotecnología, ETS Ingenieros Agrónomos, UPM, Madrid, Spain
4 Servicio de Alergia, Hospital Universitario Niño Jesús, Madrid, Spain
1 To whom correspondence should be addressed; e-mail: iain.wilson{at}boku.ac.at
Received on September 26, 2006; revised on November 2, 2006; accepted on November 5, 2006
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 ß1,2-xylose and core 
1,3-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.
Key words: allergy / glycan / orange
* These authors contributed equally to this work.