Presence of an O-glycosidically linked hexasaccharide in fetuin.
Presence of an O-glycosidically linked hexasaccharide in fetuin.
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DOI：
10.1016/s0021-9258(18)47707-1
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发表时间：
1987-11
期刊：
影响因子：
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通讯作者：
Albert S. B. Edge;R. Spiro
中科院分区：
文献类型：
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作者：
Albert S. B. Edge;R. Spiro
通过凝胶过滤、薄层和阴离子交换色谱对通过碱性硼氢化物处理从胎球蛋白中释放的O-连接碳水化合物单元进行检查表明，除了先前描述的四糖和三糖之外，该糖蛋白中还存在酸性含葡糖胺的六糖。通过外切糖苷酶消化、高碘酸盐氧化、甲基化分析以及肼-亚硝酸裂解，确定六糖的结构为NeuAc α 2—3Gal beta 1—3[NeuAc α 2—3Gal beta 1—4GlNAc beta 1—6]GalNAc。当对还原的脱唾液酸六糖进行后一过程时，产生了Gal-2-脱氧半乳糖醇和Gal-脱水甘露糖，它们被证明分别衍生自Gal-N-乙酰半乳糖胺醇和Gal-GlcNAc序列。 Gal-脱水甘露糖二糖与[14C]甲胺的还原胺化允许将其键鉴定为1-4。虽然肺炎双球菌内切-α-DN-乙酰半乳糖胺酶作用于脱唾液酸胎球蛋白，释放出不含唾液酸的四糖和三糖 (Gal beta 1-3GalNAc)，但该酶不会裂解脱唾液酸六糖 (Gal beta 1-3 [Gal beta 1-4GlcNAc beta 1-6] GalNAc) 的肽连接。根据氨基半乳糖醇分析，每个胎球蛋白分子的 O-连接六糖、四糖和三糖的数量分别确定为 0.2、0.7 和 2.1。胎球蛋白中不存在含有 O-连接的 N-乙酰氨基葡萄糖的四糖或五糖，表明这种糖的附着是一个限速步骤。此外，六糖的有限出现可能表明向Gal beta 1-3GalNAc添加唾液酸以形成NeuAc α 2-3Gal连接阻止了GlcNAc转移酶在GalNAc残基上形成分支点的作用。
Examination by gel filtration, thin layer and anion exchange chromatography of the O-linked carbohydrate units released from fetuin by alkaline borohydride treatment indicated the presence in this glycoprotein of an acidic glucosamine-containing hexasaccharide in addition to the previously described tetra- and trisaccharides. The structure of the hexasaccharide was determined to be NeuAc alpha 2—3Gal beta 1—3[NeuAc alpha 2—3Gal beta 1—4GlNAc beta 1—6]GalNAc, on the basis of exoglycosidase digestion, periodate oxidation, and methylation analysis as well as hydrazine-nitrous acid fragmentation. The latter procedure when carried out on the reduced asialohexasaccharide yielded Gal—2-deoxygalactitol and Gal—anhydromannose which were shown to be derived, respectively, from Gal—N-acetylgalactosaminitol and Gal—GlcNAc sequences. Reductive amination of the Gal—anhydromannose disaccharide with [14C] methylamine permitted identification of its linkage as 1—4. While Diplococcus pneumoniae endo-alpha-DN-acetylgalactosaminidase acting on asialofetuin released the sialic acid-free tetra- and trisaccharides (Gal beta 1—3GalNAc), this enzyme did not cleave the peptide attachment of the asialohexasaccharide (Gal beta 1—3 [Gal beta 1—4GlcNAc beta 1—6] GalNAc). The number of O-linked hexa-, tetra-, and trisaccharides per fetuin molecule was determined to be 0.2, 0.7, and 2.1, respectively, on the basis of galactosaminitol analyses. The absence of O-linked N-acetylglucosamine-containing tetra- or pentasaccharides in fetuin suggest that the attachment of this sugar is a rate-limiting step; furthermore, the limited occurrence of the hexasaccharide may indicate that the addition of sialic acid to Gal beta 1—3GalNAc to form the NeuAc alpha 2—3Gal linkage precludes action of the GlcNAc transferase to form the branch point on the GalNAc residue.