Purification and some chemical properties of 30 kDa Ginkgo biloba glycoprotein, which reacts with antiserum against β1→2 xylose-containing N-glycans

From the seeds of Ginkgo biloba, a glycoprotein, which is a major component that reacts with an antiserum against β1→2 xylose-containing N-glycans, has been purified and characterized. The N-terminal amino acid sequence of the purified glycoprotein was H-K-A-N-X-V-T-V-A-F-V-M-T-Q-H-L-L-F-G-Q-. The molecular mass was estimated to be 17 kDa and 16 kDa by SDS-PAGE under reducing conditions, however, the molecular mass of this glycoprotein in the native state was 30,762 by MALDI-TOF MS, suggesting that this glycoprotein consists of two subunits; one is glycosylated and the other is not. The structure of N-glycan linked to this glycoprotein (designated 30 kDa GBGP) was identified as Man₃Fuc₁Xyl₁GlcNAc₂, which is the predominant N-glycan linked to the storage glycoproteins in the same seeds (Kimura, Y et al. (1998) Biosci. Biotechnol. Biochem. 62, 253-261). From the peptic digest of the carboxymethylated glycosylated subunit, one glycopeptide was purified by RP-HPLC and the amino acid sequence was identified as H-K-A-N-N(Man₃Fuc₁Xyl₁Glc-NAc ₂)-V-T-V-A-F, which corresponded to the N-terminal amino acid sequence.