EFFECTS OF GLYCOSYLATION ON THE CONFORMATION AND DYNAMICS OF O-LINKED GLYCOPROTEINS - C-13 NMR-STUDIES OF OVINE SUBMAXILLARY MUCIN
EFFECTS OF GLYCOSYLATION ON THE CONFORMATION AND DYNAMICS OF O-LINKED GLYCOPROTEINS - C-13 NMR-STUDIES OF OVINE SUBMAXILLARY MUCIN
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DOI：
10.1021/bi00439a030
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发表时间：
1989-06-27
期刊：
影响因子：
2.9
通讯作者：
SHOGREN, R
中科院分区：
文献类型：
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作者：
GERKEN, TA;BUTENHOF, KJ;SHOGREN, R
天然和顺序去糖基化的绵羊颌下粘蛋白（OSM）的碳-13核磁共振光谱研究已进行检查糖基化的影响上的构象和动力学的肽核心的O-连接的糖蛋白。OSM是一种大的非小叶糖蛋白，其中近三分之一的氨基酸残基是Ser和Thr，它们被α-葡萄糖基化。Neu-NAc（2-6）α- GalNAc-二糖。β-完整和脱唾液酸粘蛋白中糖基化的Ser和Thr残基的碳共振显示出相当大的化学位移异质性，当完全除去碳水化合物时，其合并成单一的尖锐共振。这种化学位移的异质性是由于肽序列的变异性，并建议反映存在的肽核心的序列依赖性构象。这些不同的构象被认为是由GalNAc残基与相邻肽残基的空间相互作用决定的。载脂蛋白粘蛋白中不存在化学位移异质性表明肽-碳水化合物空间相互作用的损失，与更松弛的随机卷曲结构一致。基于13 C弛豫行为（T1和NOE），α-Al 2 O3的动力学可以被描述为：碳对于每种氨基酸类型和糖基化状态似乎是独特的，α-碳迁移率按Gly > Ala = Ser > Thr. mchgt.单糖基化丝氨酸/苏氨酸二糖连接的Ser/Thr。α-糖基化的Ser和Thr的碳比它们在脱辅基粘蛋白中的非糖基化的对应物受到更多的限制，而碳水化合物侧链长度的影响（即，去唾液酸粘蛋白相对于天然粘蛋白）对Ser和Thr残基动力学的影响相对较小。非糖基化的Gly残基在去除GalNAc后也表现出运动增加;因此，糖基化的影响延伸到直接结合碳水化合物的氨基酸以外的残基。这些结果与通过光散射技术测定的同一系列改性粘蛋白分子尺寸的变化一致[Shogren等人（本期前一篇论文）]。两者合计，这些结果进一步表明，粘蛋白具有高度扩展的构象，其由肽核心和O-连接的GalNAc残基之间的空间相互作用主导。
Carbon-13 NMR spectroscopic studies of native and sequentially deglycosylated ovine submaxillary mucin (OSM) have been performed to examine the effects of glycosylation on the conformation and dynamics of the peptide core of O-linked glycoproteins. OSM is a large nonglobular glycoprotein in which nearly one-third of the amino acid residues are Ser and Thr which are glycoslyated by the .alpha.-Neu-NAc(2-6).alpha.-GalNAc-disaccharide. The .beta.-carbon resonances of glycosylated Ser and Thr residues in intact and asialo mucin display considerable chemical shift heterogeneity which, upon the complete removal of carbohydrate, coalesces to single sharp resonances. This chemical shift heterogeneity is due to peptide sequence variability and is proposed to reflect the presence of sequence-dependent conformations of the peptide core. These different conformations are thought to be determined by steric interactions of the GalNAc residue with adjacent peptide residues. The absence of chemical shift heterogeneity in apo mucin is taken to indicate a loss in the peptide-carbohydrate steric interactions, consistent with a more relaxed random coiled structure. On the basis of the 13C relaxation behavior (T1 and NOE) the dynamics of the .alpha.-carbons appear to be unique to each amino acid type and glycosylation state, with .alpha.-carbon mobilities decreasing in the order Gly > Ala = Ser > Thr .mchgt. monoglycosylated Ser/Thr .gtorsim. disaccharide linked Ser/Thr. The .alpha.-carbons of glycosylated Ser and Thr are considerably more constrained than their nonglycosylated counterparts in apo mucin, while the effects of carbohydrate side chain length (i.e., asialo vs native mucin) on the dynamics of the Ser and Thr residues is relatively small. The nonglycosylated Gly residue also exhibits an increase in motion upon removal of GalNAc; thus, the effects of glycosylation extend to residues beyond the amino acids directly bound to carbohydrate. These results are consistent with the changes in molecular dimensions determined by light-scattering techniques for the same series of modified mucins [Shogren et al. (preceding paper in this issue)]. Taken together, these results further demonstrate that mucins possess a highly expanded conformation that is dominated by steric interactions between the peptide core and the O-linked GalNAc residue.