Department of Chemical Engineering, Tsinghua University, Beijing, China.
J Phys Chem B. 2012 Jan 12;116(1):390-400. doi: 10.1021/jp203926r. Epub 2011 Dec 21.
Glycosylation is one of the most common post-translational modifications in the biosynthesis of protein, but its effect on the protein conformational transitions underpinning folding and stabilization is poorly understood. In this study, we present a coarse-grained off-lattice 46-β barrel model protein glycosylated by glycans with different hydrophobicity and glycosylation sites to examine the effect of glycans on protein folding and stabilization using a Langevin dynamics simulation, in which an H term was proposed as the index of the hydrophobicity of glycan. Compared with its native counterpart, introducing glycans of suitable hydrophobicity (0.1 < H < 0.4) at flexible peptide residues of this model protein not only facilitated folding of the protein but also increased its conformation stability significantly. On the contrary, when glycans were introduced at the restricted peptide residues of the protein, only those hydrophilic (H = 0) or very weak hydrophobic (H < 0.2) ones contributed slightly to protein stability but hindered protein folding due to increased free energy barriers. The glycosylated protein retained the two-step folding mechanism in terms of hydrophobic collapse and structural rearrangement. Glycan chains located in a suitable site with an appropriate hydrophobicity facilitated both collapse and rearrangement, whereas others, though accelerating collapse, hindered rearrangement. In addition to entropy effects, that is, narrowing the space of the conformations of the unfolded state, the presence of glycans with suitable hydrophobicity at suitable glycosylation site strengthened the folded state via hydrophobic interaction, that is, the enthalpy effect. The simulations have shown both the stabilization and the destabilization effects of glycosylation, as experimentally reported in the literature, and provided molecular insight into glycosylated proteins. The understanding of the effects of glycans with different hydrophobicities on the folding and stability of protein, as attempted by the present work, is helpful not only to explain the stabilization and destabilization effect of real glycoproteins but also to design protein-polymer conjugates for biotechnological purposes.
糖基化是蛋白质生物合成中最常见的翻译后修饰之一，但人们对其在蛋白质折叠和稳定化所必需的构象转变中的作用知之甚少。在这项研究中，我们提出了一种粗粒无网格 46-β 桶模型蛋白，该蛋白通过不同疏水性和糖基化位点的聚糖进行糖基化，以使用朗之万动力学模拟研究聚糖对蛋白折叠和稳定化的影响，其中 H 项被提出作为糖基化聚糖疏水性的指标。与天然蛋白相比，在该模型蛋白的柔性肽残基上引入具有合适疏水性（0.1<H<0.4）的聚糖不仅促进了蛋白的折叠，而且显著增加了其构象稳定性。相反，当糖基化在蛋白的受限肽残基上进行时，只有那些亲水（H=0）或非常弱疏水性（H<0.2）的聚糖对蛋白稳定性略有贡献，但由于增加了自由能势垒而阻碍了蛋白折叠。糖基化蛋白保留了疏水塌陷和结构重排的两步折叠机制。位于合适位置且疏水性合适的糖基化链促进了塌陷和重排，而其他糖基化链尽管促进了塌陷，但阻碍了重排。除了熵效应，即缩小未折叠状态构象的空间外，具有合适疏水性的聚糖位于合适的糖基化位点时通过疏水相互作用增强了折叠状态，即焓效应。模拟结果显示了糖基化的稳定和失稳效应，正如文献中实验报道的那样，并为糖基化蛋白提供了分子见解。本研究尝试了解不同疏水性聚糖对蛋白折叠和稳定性的影响，这不仅有助于解释真实糖蛋白的稳定和失稳效应，还有助于设计用于生物技术目的的蛋白-聚合物缀合物。
