Glycobiology Advance Access published online on November 9, 2006
Glycobiology, doi:10.1093/glycob/cwl068
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© The Author 2006. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org
Molecular and immunological characterisation of the glycosylated orange allergen Cit s 1
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1 Department für Chemie, Universität für Bodenkultur, Muthgasse 18, A-1190 Wien, Austria
2 Unidad de Bioquímica, Departamento de Biotecnología, E.T.S. Ingenieros Agrónomos, UPM, Madrid, Spain
3 Servicio de Alergia, Hospital Universitario Niño Jesús, Madrid, Spain
To whom correspondence should be addressed: 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) bind a number of proteins in orange extract, including Cit s 1, a germin-like protein. In the present study, we have analysed its immunological cross-reactivity and its molecular nature. Sera from many of the patients examined recognise 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 as compared to 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. Due 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, therefore, explain the immunological cross-reactive properties of Cit s 1 as well as its equivocal nature as a clinically-relevant allergen.