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.

中文翻译：

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蛇binding种子凝集素（SGSL）中的配体结合和保留。晶体学，热力学和分子动力学研究

丝瓜种子凝集素（SGSL）是II型核糖体失活蛋白（RIP）的无毒同源物，包含催化结构域和凝集素结构域。进行了等温滴定热法（ITC）测定蛋白质与LacNAc，Lac，Gal，Me-α-Gal的相互作用，并确定了天然蛋白质及其与Lac的复合物的晶体结构。Me-α-Gal配合物的晶体结构已经确定。虽然晶体结构显示存在两个糖结合位点，但在凝集素链的两个结构域中每个域上都存在一个，但ITC测量表明仅存在一个结合位点。为了解决此异常，对天然蛋白质及其与Me-α-Gal和Lac形成的复合物进行了分子动力学（MD）模拟。减少两条链之间的链间二硫键后，还对该蛋白质进行了模拟。晶体结构和模拟证实了蛋白质结构的鲁棒性，而与是否存在二硫键无关。模拟表明，尽管两个位点可以结合糖，但是在动态情况下仅保留一个位点的配体。因此，研究揭示了配体的结合与保留之间的微妙关系。