Friedman M L, Wermeling J R, Halsall H B
Biochem J. 1986 May 15;236(1):149-53. doi: 10.1042/bj2360149.
Little is known of the relationships that may exist among the three principal functionalities of glycoproteins. Orosomucoids of closely defined N-acetylneuraminic acid content were examined for evidence of influence of N-acetylneuraminic acid content on the physical properties of the glycoprotein. Fluorescence spectroscopy gave no indication of conformational change in the protein core upon desialylation. Small changes in the chromatographic partition coefficient, sigma, and thermal stability, Td, are interpreted to reflect loss of water of hydration and increased glycan stem-protein interaction without a major repositioning of the chains. Ligand-binding measurements indicate no alteration in the hydrophobic binding domain and a possible interaction between chlorpromazine and N-acetylneuraminic acid. All changes seen are progressive and occur through a region where changes in biological activity are not found. It is suggested that the dependence of biological activity on N-acetylneuraminic acid content in orosomucoid reflects, not coupled changes in protein conformation, but a charge-density-related interaction such that, below a contribution of four or five N-acetylneuraminic acid residues, activity is modified.
关于糖蛋白的三种主要功能之间可能存在的关系，我们所知甚少。研究了具有严格定义的N-乙酰神经氨酸含量的类粘蛋白，以寻找N-乙酰神经氨酸含量对糖蛋白物理性质影响的证据。荧光光谱法未显示去唾液酸化后蛋白质核心的构象变化。色谱分配系数sigma和热稳定性Td的微小变化被解释为反映了水化水的损失以及聚糖茎与蛋白质相互作用的增加，而链没有发生重大重新定位。配体结合测量表明疏水结合域没有改变，并且氯丙嗪与N-乙酰神经氨酸之间可能存在相互作用。所有观察到的变化都是渐进的，并且发生在未发现生物活性变化的区域。有人提出，类粘蛋白中生物活性对N-乙酰神经氨酸含量的依赖性反映的不是蛋白质构象的耦合变化，而是与电荷密度相关的相互作用，即，在四个或五个N-乙酰神经氨酸残基的贡献以下，活性会被改变。
