The State Key Laboratory of Protein and Plant Gene Research, School of Life Sciences, Peking-Tsinghua Center for Life Sciences, Peking University, Beijing, 100871, China.
Protein Sci. 2018 Apr;27(4):886-892. doi: 10.1002/pro.3381. Epub 2018 Mar 12.
Catharanthus roseus Receptor-Like Kinase 1-like (CrRLK1L) proteins contain two tandem malectin-like modules in their extracellular domains (ECDs) and function in diverse signaling pathways in plants. Malectin is a carbohydrate-binding protein in animals and recognizes a number of diglucosides; however, it remains unclear how the two malectin-like domains in the CrRLK1L proteins sense the ligand molecule. In this study, we reveal the crystal structures of the ECDs of ANXUR1 and ANXUR2, two CrRLK1L members in Arabidopsis thaliana that have critical functions in controlling pollen tube rupture during the fertilization process. We show that the two malectin-like domains in these proteins pack together to form a rigid architecture. Unlike animal malectin, these malectin-like domains lack residues involved in binding to the diglucosides, suggesting that they have a distinct ligand-binding mechanism. A cleft is observed between the two malectin-like domains, which might function as a potential ligand-binding pocket.
长春花受体样激酶 1 样（CrRLK1L）蛋白在其细胞外结构域（ECD）中含有两个串联的甘露糖结合蛋白样模块，并在植物中的多种信号通路中发挥作用。甘露糖结合蛋白是动物中的一种碳水化合物结合蛋白，可识别多种二葡萄糖苷；然而，目前尚不清楚 CrRLK1L 蛋白中的两个甘露糖结合蛋白样结构域如何感知配体分子。在这项研究中，我们揭示了拟南芥中两个 CrRLK1L 成员 ANXUR1 和 ANXUR2 的 ECD 的晶体结构，它们在控制受精过程中花粉管破裂方面具有关键功能。我们表明，这两种蛋白中的两个甘露糖结合蛋白样结构域彼此紧密结合形成刚性结构。与动物甘露糖结合蛋白不同，这些甘露糖结合蛋白样结构域缺乏与二葡萄糖苷结合的残基，这表明它们具有独特的配体结合机制。在两个甘露糖结合蛋白样结构域之间观察到一个裂隙，该裂隙可能作为潜在的配体结合口袋。
