Role of glycosylation on the conformation and chain dimensions of O-linked glycoproteins: light-scattering studies of ovine submaxillary mucin.
Role of glycosylation on the conformation and chain dimensions of O-linked glycoproteins: light-scattering studies of ovine submaxillary mucin.
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DOI：
10.1021/bi00439a029
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发表时间：
1989-06
期刊：
影响因子：
2.9
通讯作者：
Randal Shogren;Randal Shogren;Thomas A. Gerken;N. Jentoft
中科院分区：
文献类型：
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作者：
Randal Shogren;Randal Shogren;Thomas A. Gerken;N. Jentoft
利用光散射和圆二色性研究了天然、去唾液酸和去糖基化（apo）绵羊颌下腺粘蛋白（OSM）的碳水化合物对粘糖蛋白构象和链尺寸的影响。OSM是一种大糖蛋白，被二糖α-NeuNAc（2-6）α-GalNAc-O-Ser/Thr广泛O-糖基化。均方根回转半径，（Rg 2）1/2，和流体动力学半径，Rh，OSM及其衍生物的测量进行了作为分子量的函数，通过使用静态和动态光散射技术。计算结果与描述高分子链伸展尺寸的蠕虫链模型相吻合。通过使用该模型，获得了每个氨基酸残基的长度h和作为链刚度的量度的持续长度q的值。然后使用这些值来评估完整OSM及其部分和完全去糖基化衍生物的构象和链延伸程度。发现天然和脱唾液酸粘蛋白是高度延伸的无规卷曲，其中脱唾液酸粘蛋白具有比完整粘蛋白稍微更少延伸的结构。在完全去除碳水化合物侧链后，完整和脱唾液酸粘蛋白的延伸结构特征塌陷至变性球状蛋白的典型链尺寸。还通过使用N-乙酰基-O-（GalNAc）-Thr-N-甲基酰胺作为天然和脱唾液酸粘蛋白的起始构象的概率图进行基于旋转异构状态模型的构象分析。结果表明，天然粘蛋白中的糖基化和非糖基化残基都可以占据构象空间的小区域，该构象空间具有小于-60度的phi的-90度和小于180度的psi的60度，而发现稍微更宽的范围适合脱唾液酸粘蛋白。这些粘蛋白的建议获得的构象是一致的圆二色光谱。载脂蛋白粘蛋白的phi和psi值的范围明显更大，这是从其圆二色谱和增加的灵活性所预期的。这些结果表明扩展的粘蛋白结构是肽核心糖基化的直接结果。这些观察结果与早期研究的结果一起表明，O-连接的GalNAc残基与肽核心的空间相互作用是主要负责扩展粘蛋白结构，并且这些扰动延伸到非糖基化的氨基酸残基。这种膨胀的粘蛋白构象必须是这些分子在溶液中的粘弹性的重要决定因素。
The effect of carbohydrate on the conformation and chain dimensions of mucous glycoproteins was investigated by using light-scattering and circular dichroism studies of native, asialo, and deglycosylated (apo) ovine submaxillary gland mucin (OSM). OSM is a large glycoprotein that is extensively O-glycosylated by the disaccharide alpha-NeuNAc(2-6)alpha-GalNAc-O-Ser/Thr. Measurements of root mean square radius of gyration, (Rg2)1/2, and hydrodynamic radius, Rh, for OSM and its derivatives were carried out as a function of molecular weight by using static and dynamic light-scattering techniques. The results were fit to the wormlike chain model for describing the dimensions of extended polymer chains. By use of this model, values of h, the length per amino acid residue, and q, the persistence length, which is a measure of chain stiffness, were obtained. These values were then used to assess the conformation and degree of chain extension of intact OSM and its partially and totally deglycosylated derivatives. Native and asialo mucin are found to be highly extended random coils, with asialo mucin having a somewhat less extended structure than intact mucin. Upon the complete removal of the carbohydrate side chains, the extended structure characteristic of intact and asialo mucin collapses to chain dimensions typical of denatured globular proteins. Conformational analyses based on the rotational isomeric state model were also performed by using the probability maps of N-acetyl-O-(GalNAc)-Thr-N-methylamide as starting conformations for native and asialo mucin. The results suggest that both the glycosylated and nonglycosylated residues in native mucin may occupy a small region of conformational space having -90 degrees less than phi less than -60 degrees and 60 degrees less than psi less than 180 degrees, while a slightly broader range is found to fit asialo mucin. The proposed conformations obtained for these mucins are consistent with their circular dichroism spectra. Significantly larger ranges of phi and psi values were obtained for apo mucin, as would be expected from its circular dichroism spectra and increased flexibility. These results indicate the expanded mucin structure is the direct result of peptide core glycosylation. These observations together with the results of earlier studies indicate that steric interactions of the O-linked GalNAc residue with the peptide core are primarily responsible for the expanded mucin structure and that these perturbations extend to the nonglycosylated amino acid residues. This expanded mucin conformation must be a significant determinant of the viscoelastic properties of these molecules in solution.