Molecular Biophysics Unit, Indian Institute of Science, Bangalore, India.
Glycobiology. 2018 Dec 1;28(12):968-977. doi: 10.1093/glycob/cwy072.
Snake gourd seed lectin (SGSL) is a non-toxic homolog of type II ribosome-inactivating proteins (RIPs) which contain a catalytic domain and a lectin domain. Isothermal titration calorimetry (ITC) measurements of the interactions of the protein with LacNAc, Lac, Gal, Me-α-Gal were carried out and the crystal structures of the native protein and its complex with Lac were determined. The crystal structure of the Me-α-Gal complex has already been determined. While the crystal structure showed the presence of two-sugar-binding sites, one on each of the two domains of the lectin chain, ITC measurements indicated the presence of only one binding site. In order to resolve this anomaly, molecular dynamics (MD) simulations were carried out on the native protein and on its complexes with Me-α-Gal and Lac. Simulations were also performed on the protein after reducing the inter-chain disulfide bridge between the two chains. The crystal structures and the simulations confirmed the robustness of the protein structure, irrespective of the presence or absence of the disulfide bridge. The simulations indicated that although two sites can bind sugar, only the ligand at one site is retained in a dynamic situation. The studies thus bring out the subtle relationship between binding and retention of the ligand.
蛇瓜籽 lectin（SGSL）是一种无毒的 II 型核糖体失活蛋白（RIPs）的同源物，它包含一个催化结构域和一个 lectin 结构域。采用等温热滴定法（ITC）测量了蛋白质与 LacNAc、Lac、Gal、Me-α-Gal 的相互作用，并确定了天然蛋白质及其与 Lac 复合物的晶体结构。Me-α-Gal 复合物的晶体结构已经确定。虽然晶体结构显示了存在两个糖结合位点，一个位于 lectin 链的两个结构域上，但 ITC 测量表明只存在一个结合位点。为了解决这一异常，对天然蛋白质及其与 Me-α-Gal 和 Lac 的复合物进行了分子动力学（MD）模拟。还对还原了两条链之间的链间二硫键后的蛋白质进行了模拟。晶体结构和模拟实验证实了蛋白质结构的稳健性，无论是否存在二硫键。模拟实验表明，尽管两个位点可以结合糖，但只有一个位点的配体在动态情况下被保留。因此，这些研究揭示了配体结合和保留之间的微妙关系。
