Centro de Química e Bioquímica and Departamento de Química e Bioquímica, Faculdade de Ciências, Universidade de Lisboa, 1749-016 Lisboa, Portugal.
J Phys Chem B. 2013 Jun 27;117(25):7507-17. doi: 10.1021/jp401066v. Epub 2013 Jun 12.
Glutathione is a small peptide with a crucial role in living organisms. This molecule is found in Nature in both reduced (GSH) and oxidized (GSSG) forms and a high GSH/GSSG ratio is essential to the cell. Glutathione is also present in several enzymatic reactions and can be found in many protein structures. As small peptides, these molecules do not have a defined structure in solution and are able to sample a broad conformational space. In addition, both molecules have several titration sites (four in GSH and six in GSSG) and their conformational space is inevitably influenced by pH. Here, we present a detailed conformational study of GSH and GSSG in a range of pH values, together with a full pH titration of these molecules. We performed constant-pH MD simulations of GSH and GSSG at 24 pH values in a total of 14.4 μs (300 ns per pH value). We obtained the two titration curves and the pKa values for all titrable groups with good agreement with experimental data. We also observed that GSH and GSSG have a large conformational variability in solution and their structural preferences are not significantly affected upon binding to proteins. Some exceptions were found and investigated in detail.
谷胱甘肽是一种具有重要生物学功能的小分子肽。该分子在自然界中存在还原型（GSH）和氧化型（GSSG）两种形式，高的 GSH/GSSG 比值对细胞至关重要。谷胱甘肽还参与多种酶促反应，并存在于许多蛋白质结构中。作为小分子，这些分子在溶液中没有确定的结构，可以在广泛的构象空间中进行采样。此外，这两种分子都有几个滴定部位（GSH 有四个，GSSG 有六个），其构象空间不可避免地受到 pH 值的影响。在这里，我们在一系列 pH 值下对 GSH 和 GSSG 进行了详细的构象研究，并对这些分子进行了完整的 pH 滴定。我们在总共 14.4 μs（每个 pH 值 300 ns）的 24 个 pH 值下进行了 GSH 和 GSSG 的恒 pH MD 模拟。我们得到了两条滴定曲线和所有可滴定基团的 pKa 值，与实验数据吻合良好。我们还观察到，GSH 和 GSSG 在溶液中有很大的构象可变性，它们的结构偏好在与蛋白质结合时不会受到显著影响。我们发现了一些例外，并进行了详细的研究。
