ISOLATION AND CHARACTERIZATION OF THE MAJOR OLIGOSACCHARIDE OF HUMAN-PLATELET MEMBRANE GLYCOPROTEIN GPIB
ISOLATION AND CHARACTERIZATION OF THE MAJOR OLIGOSACCHARIDE OF HUMAN-PLATELET MEMBRANE GLYCOPROTEIN GPIB
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DOI：
10.1042/bj2050081
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发表时间：
1982-01-01
影响因子：
4.1
通讯作者：
CLAMP, JR
中科院分区：
文献类型：
--
作者：
JUDSON, PA;ANSTEE, DJ;CLAMP, JR
用胰凝乳蛋白酶处理完整的人血小板，释放出一种糖多肽，它来源于主要的膜糖蛋白GPIb。该糖肽含有59%的碳水化合物，并富含丝氨酸、苏氨酸和脯氨酸。在NaBH_4存在下，用碱处理糖肽几乎可以释放出所有的碳水化合物。主要成分（占释放糖的80%）经过纯化，显示为含有唾液酸、半乳糖、N-乙酰基葡萄糖胺和N-乙酰基-半乳糖胺醇的六糖，摩尔比为2：2：1：1。根据粘液型糖蛋白的已知生物合成途径，提出了这种六糖的两种可能结构。该数据与4种糖多肽中1个氨基酸上存在O-糖苷键连接的寡糖一致。糖蛋白Ib是一种膜结合的粘液型糖蛋白。这些数据与血小板粘附于受损血管壁暴露的内皮下的过程中O-寡糖的发生一致。GPIb的糖肽部分在这个过程中的可能作用进行了研究。在测试浓度下，主要低聚糖和糖肽本身都不能抑制利托菌素诱导的血小板凝集。GPIb分子在细胞表面的碳水化合物部分显然相互作用，形成对大分子的屏障。这种屏障在调节血小板功能中发挥重要作用。
Treatment of intact human platelets with chymotrypsin released a glycopolypeptide that was derived from the major membrane glycoprotein, GPIb. The glycopolypeptide contained 59% carbohydrate on a molar basis and was rich in serine, threonine and proline. Almost all the carbohydrate could be released from the glycopolypeptide by treatment with alkali in the presence of NaBH4. The major component (comprising 80% of the released sugar) was purified and shown to be a hexasaccharide containing sialic acid, galactose, N-acetylglucosamine and N-acetyl-galactosaminitol, in the molar ratios 2:2:1:1. Two possible structures for this hexasaccharide are proposed on the basis of the known biosynthetic pathways of mucus-type glycoproteins. The data is consistent with the occurrence of an O-glycosidically linked oligosaccharide on 1 amino acid in 4 of the glycopolypeptides. Glycoprotein Ib can best be described as a membrane-bound mucus-type glycoproteins. The data are consistent with the occurrence of an O-oligosaccharide in the process by which platelets adhere to the exposed subendothelium of damaged blood-vessel walls. The possible role of the glycopolypeptide portion of GPIb in this process was investigated. Neither the major oligosaccharide nor the glycopolypeptide itself inhibited ristocetin-induced platelet agglutination at the concentrations tested. The carbohydrate moieties of GPIb molecules at the cell surface apparently interact to form a barrier to macromolecules. Such a barrier could play a major role in modulating platelet function.