Conformation of the glycotripeptide repeating unit of antifreeze glycoprotein of polar fish as determined from the fully assigned proton n.m.r. spectrum.
Conformation of the glycotripeptide repeating unit of antifreeze glycoprotein of polar fish as determined from the fully assigned proton n.m.r. spectrum.
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根据完全指定的质子核磁共振确定的极地鱼抗冻糖蛋白糖三肽重复单元的构象。
DOI：
10.1111/j.1399-3011.1986.tb03270.x
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发表时间：
1986
期刊：
影响因子：
--
通讯作者：
Feeney,RE
中科院分区：
文献类型：
--
作者：
Bush,CA;Feeney,RE
极地鱼的抗冻糖蛋白具有简单的糖三肽重复结构，对于具有相似但更复杂结构的粘蛋白糖蛋白来说，可能是一种特别简单的构象模式。完全指定的质子核磁共振光谱证实了侧链六吡喃糖的异头构型，并且 α GalNAc 和 β Gal 残基的偶联常数显示两者都处于预期的 4C1chair 构象中。 (Ala-Thr-Ala)n 重复单元的每个质子的单一共振分配与长程核奥弗豪瑟效应 (n.O.e.) 的观察相结合，意味着三重重复构象。两个丙氨酸的共振是不同的，并且可以通过 n.O.e. 分配到它们在肽序列中的正确位置。在 α 质子信号饱和的酰胺质子共振中观察到。所有三个肽残基的酰胺质子耦合常数相似，意味着肽主链扭转角 CN 的范围有限。大型 n.O.e.在序列中其前面的残基的酰胺质子和 α 质子之间观察到的这一点意味着肽二面角 CC 具有较大的正值。通过观察苏氨酰残基的α和β质子之间的耦合常数来限制侧链二面角的可能值。 n.O.e. 的观察GalNAc 的异头质子和苏氨酰侧链质子之间的差异提供了有关二糖和肽之间 α 糖苷键构象的信息。不详观察到的β糖苷键的质子之间表明二糖的构象，并且GalNAc残基的大酰胺质子偶联常数显示出反质子关系。光谱导出的数据与构象能计算相结合，给出了抗冻糖蛋白的构象模型，其中二糖侧链的疏水表面紧密包裹在三重左手螺旋肽主链上。二糖的亲水侧排列，以便它们可以与冰晶面结合，该冰晶面垂直于抑制正常晶体生长的快速生长轴。
With its simple glycotripeptide repeating structure the antifreeze glycoprotein of polar fish may be an especially simple conformational mode for mucin glycoproteins with similar but more complex structures. The fully assigned proton n.m.r. spectrum confirms the anomeric configurations of the hexapyranosidic sugars of the side chains and the coupling constants of the α GalNAc and the β Gal residues show both to be in the expected4C1chair conformation. The assignment of a single resonance for each proton of the (Ala‐Thr‐Ala)nrepeat unit coupled with the observation of long range nuclear Overhauser effects (n.O.e.) implies a three‐fold repeating conformation. The resonances of the two alanines are distinct and can be assigned to their correct positions in the peptide sequence by n.O.e. observed at the amide proton resonances on saturation of the α proton signals. The amide proton coupling constants of all three peptide residues are similar and imply a limited range of peptide backbone torsion angles,CN. The large n.O.e. which has been observed between the amide proton and the α proton of the residue preceding it in the sequence implies large positive values for the peptide dihedral angle,CC. Limits are placed on possible values of side chain dihedral angles by the observation of the coupling constant between the α and β protons of the threonyl residue. The observation of n.O.e. between the anomeric proton of GalNAc and the threonyl side chain protons gives information on the conformation of the α glycosidic linkage between the disaccharide and the peptide. n.O.e. observed between the protons of the β glycosidic linkage indicates the conformation of the disaccharide and the large amide proton coupling constant of the GalNAc residue shows atransproton relationship. The spectroscopically derived data have been combined with conformational energy calculations to give a conformational model for antifreeze glycoprotein in which the hydrophobic surfaces of the disaccharide side chains are wrapped closely against a three‐fold left handed helical peptide backbone. The hydrophilic sides of the disaccharides are aligned so that they may bind to the ice crystal face, which is perpendicular to the fast growth axis inhibiting normal crystal growth.