Purification and Substrate Specificity of A Ginkgo biloba Glycosidase Active in β-1,2-Xylosidic Linkage in Plant Complex Type N -Glycans

Purification and molecular characterization of a truncated-type Ara h 1, a major peanut allergen: oligomer structure, antigenicity, and glycoform

Peanut allergies are among the most severe food allergies, and several allergenic proteins referred to as Ara h 1-Ara h 17 have been identified from peanut seeds. The molecular characterization of Ara h 1 (63 kDa), a glycosylated allergen, has almost been completed, and the occurrence of two homologous genes (clone 41B and clone P17) has been identified. In this study, we found a new variant of Ara h 1 i.e. 54 kDa, in which the N-terminal amino acid sequence was EGREGEQ-, indicating that the N-terminal domain of 63 kDa Ara h 1 had been removed. This new isoform was obtained from the run-through fraction of hydrophobic interaction chromatography while 63 kDa Ara h 1 was tightly bound to the hydrophobic resins, suggesting that the removal of the N-terminal domain resulted in extreme hydrophilic properties. We found that 63 kDa Ara h 1 occurs as higher order homo-oligomeric conformations such as decamer or nonamer, while 54 kDa Ara h 1 occurs exclusively as a homotrimer, indicating that the N-terminal domain of the 63 kDa molecule may be involved in higher order oligomerization. When antisera from peanut-allergic patients were treated with both the Ara h 1 molecules, the immunoglobulin E (IgE) antibodies in these sera reacted with each Ara h 1 molecule, suggesting that the C-terminal as well as the N-terminal domains of Ara h 1 contribute significantly to the epitope formations of this peanut glycoallergen. Furthermore, the glycoform analyses of N-glycans linked to 63 kDa and 54 kDa Ara h 1 subunits revealed that both typical high-mannose type and β-xylosylated type N-glycans are linked to the molecules. The cross-reactivity of IgE against Ara h 1 in the serum of one peanut allergy patient was completely lost by de-N-glycosylation, indicating the N-glycan of Ara h 1 was the sole epitope for the Ara h 1- specific IgE in the patient.

Identification and characterization of a novel glycoprotein core xylosidase from the bacterium Elizabethkingia meningoseptica

Although core xylose on glycoproteins has been implicated in allergy, infection and other biological processes, research on core xylose modification is rare. The lack of a β-d-xylosidase that can catalytically remove the core xylose directly from glycoproteins is a reason for this. Through functional genomic analysis, we identified a glycoprotein core xylosidase and named it gpcXase I. gpcXase I is located immediately downstream of glycoprotein core fucosidase cFase I in Elizabethkingia meningoseptica. These two genes form a functional operon for glycoprotein core modifications. Three acidic residues (Asp-200, Asp-304 and Glu-649) were identified as key catalytic sites for gpcXase I activity, suggesting a unique triacdic mechanize for its activity. Asp-200 was identified a novel and essential base catalysts in the catalytic process, Asp-304 and Glu-649 was function as catalytic nucleophiles and acid catalysts, respectively. In addition, IgE-specific reactions were detected in 55% of serum samples collected from 40 allergic patients, and the reactions were significantly attenuated by removal of the core xylose of the allergen by treatment with gpcXase I. gpcXase I is a novel tool for basic and clinical glycomics.

Degradation pathway of plant complex-type N-glycans: identification and characterization of a key α1,3-fucosidase from glycoside hydrolase family 29

Plant complex-type N-glycans are characterized by the presence of α1,3-linked fucose towards the proximal N-acetylglucosamine residue and β1,2-linked xylose towards the β-mannose residue. These glycans are ultimately degraded by the activity of several glycoside hydrolases. However, the degradation pathway of plant complex-type N-glycans has not been entirely elucidated because the gene encoding α1,3-fucosidase, a glycoside hydrolase acting on plant complex-type N-glycans, has not yet been identified, and its substrate specificity remains to be determined. In the present study, we found that AtFUC1 (an Arabidopsis GH29 α-fucosidase) is an α1,3-fucosidase acting on plant complex-type N-glycans. This fucosidase has been known to act on α1,4-fucoside linkage in the Lewis A epitope of plant complex-type N-glycans. We found that this glycoside hydrolase specifically acted on GlcNAcβ1-4(Fucα1-3)GlcNAc, a degradation product of plant complex-type N-glycans, by sequential actions of vacuolar α-mannosidase, β1,2-xylosidase, and endo-β-mannosidase. The AtFUC1-deficient mutant showed no distinct phenotypic plant growth features; however, it accumulated GlcNAcβ1-4(Fucα1-3)GlcNAc, a substrate of AtFUC1. These results showed that AtFUC1 is an α1,3-fucosidase acting on plant complex-type N-glycans and elucidated the degradation pathway of plant complex-type N-glycans.

β-Galactosidase from Ginkgo biloba seeds active against β-galactose-containing N-glycans: purification and characterization

In this study, we purified an acidic β-galactosidase to homogeneity from Ginkgo biloba seeds (β-Gal’ase Gb-1) with approximately 270-fold purification. A molecular mass of the purified β-Gal’ase Gb-1 was estimated about 35 kDa by gel filtration and 32 kDa by SDS-PAGE under non-reducing condition, respectively. On the other hand, β-Gal’ase Gb-1 produced a single band with a molecular mass of 16 kDa by SDS-PAGE under reducing condition. The N-terminal amino acid sequences of 32 kDa and 16 kDa molecules were the same and identified as H-K-A-N-X-V-T-V-A-F-V-M-T-Q-H-, suggesting that β-Gal’ase Gb-1 may function as a homodimeric structure in vivo. When complex-type N-glycans containing β-galactosyl residues were used as substrates, β-Gal’ase Gb-1 showed substantial activity for β1-4 galactosyl residue and modest activity for β1-3 galactosyl residue with an optimum pH near 5.0. Based on these results, the involvement of β-Gal’ase Gb-1 in the degradation of plant complex-type N-glycans is discussed.