N-Linked Oligosaccharides of Glycoproteins from Ginkgo biloba Pollen, An Allergenic Pollen

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The pollen of Ginkgo biloba is one of the allergens that cause pollen allergy symptoms. The plant complex type N-glycans bearing β1-2 xylose and/or α1-3 fucose residue(s) linked to glycoallergens have been considered to be critical epitopes in various immune reactions. In this report, the structures of N-glycans of total glycoproteins prepared from Ginkgo biloba pollens were analyzed to confirm whether such plant complex type N-glycans occur in the pollen glycoproteins. The glycoproteins were extracted by SDS-Tris buffer. N-Glycans liberated from the pollen glycoprotein mixture by hydrazinolysis were labeled with 2-aminopyridine and the resulting pyridylaminated (PA-)N-glycans were purified by a combination of size-fractionation HPLC and reversed-phase HPLC. The structures of the PA-sugar chains were analyzed by a combination of two-dimensional sugar chain mapping, IS-MS, and MS/MS. The plant complex type structures (GlcNAc₂Man₃Xyl₁Fuc₁GlcNAc₂ (31%), GlcNAc₂Man₃Xyl₁GlcNAc₂ (5%), Man₃Xyl₁Fuc₁GlcNAc₂ (13%), GlcNAc₁Man₃ Xyl₁Fuc₁ GlcNAc₂ (8%), and GlcNAC₁Man₃Xyl₁GlcNAc₂ (17%)) have been found among the N-glycans of the glycoproteins of Ginkgo biloba pollen, which might be candidates for the epitopes involved in Ginkgo pollen allergy. The remaining 26% of the total pollen N-glycans have the typical high-mannose type structures: Man₈GlcNAc₂ (11%) and Man₆GlcNAc₂ (15%).