Molecular Biophysics Unit, Indian Institute of Science, Bangalore, Karnataka, India.
IUBMB Life. 2013 Jul;65(7):633-44. doi: 10.1002/iub.1177.
Crystal structure analysis of a galactose-specific lectin from a leguminous food crop Dolichos lablab (Indian lablab beans) has been carried out to obtain insights into its quaternary association and lectin-carbohydrate interactions. The analysis led to the identification of adenine binding sites at the dimeric interfaces of the heterotetrameric lectin. Structural details of similar adenine binding were reported in only one legume lectin, Dolichos biflorus, before this study. Here, we present the structure of the galactose-binding D. lablab lectin at different pH values in the native form and in complex with galactose and adenine. This first structure report on this lectin also provides a high resolution atomic view of legume lectin-adenine interactions. The tetramer has two canonical and two DB58-like interfaces. The binding of adenine, a non-carbohydrate ligand, is found to occur at four hydrophobic sites at the core of the tetramer at the DB58-like dimeric interfaces and does not interfere with the carbohydrate-binding site. To support the crystallographic observations, the adenine binding was further quantified by carrying out isothermal calorimetric titration. By this method, we not only estimated the affinity of the lectin to adenine but also showed that adenine binds with negative cooperativity in solution.
从豆科食用作物豇豆（印度豇豆）中分离出的半乳糖特异性凝集素进行了晶体结构分析，以深入了解其四级缔合和凝集素-碳水化合物相互作用。分析确定了在异四聚体凝集素的二聚体界面处存在腺嘌呤结合位点。在这项研究之前，只有一种豆科凝集素（多花豇豆）报道了类似的腺嘌呤结合的结构细节。在这里，我们展示了在天然状态和与半乳糖和腺嘌呤复合物中不同 pH 值下的半乳糖结合的 D. lablab 凝集素的结构。该结构报告是该凝集素的首次报道，还提供了豆科凝集素-腺嘌呤相互作用的高分辨率原子视图。四聚体具有两个典型的和两个 DB58 样的界面。发现非碳水化合物配体腺嘌呤的结合发生在四聚体的 DB58 样二聚体界面的核心处的四个疏水性位点上，并且不干扰碳水化合物结合位点。为了支持晶体学观察，通过进行等温热滴定进一步定量了腺嘌呤的结合。通过这种方法，我们不仅估计了凝集素与腺嘌呤的亲和力，还表明腺嘌呤在溶液中以负协同方式结合。
