The Plant Signaling Mechanisms Laboratory, Department of Plant Molecular Biology, University of Lausanne, 1015 Lausanne, Switzerland.
Acta Crystallogr D Struct Biol. 2018 Jul 1;74(Pt 7):671-680. doi: 10.1107/S205979831800774X. Epub 2018 Jun 27.
Complex cell-to-cell communication between the male pollen tube and the female reproductive organs is required for plant fertilization. A family of Catharanthus roseus receptor kinase 1-like (CrRLK1L) membrane receptors has been genetically implicated in this process. Here, crystal structures of the CrRLK1Ls ANXUR1 and ANXUR2 are reported at 1.48 and 1.1 Å resolution, respectively. The structures reveal a novel arrangement of two malectin-like domains connected by a short β-hairpin linker and stabilized by calcium ions. The canonical carbohydrate-interaction surfaces of related animal and bacterial carbohydrate-binding modules are not conserved in plant CrRLK1Ls. In line with this, the binding of chemically diverse oligosaccharides to ANXUR1 and HERCULES1 could not be detected. Instead, CrRLK1Ls have evolved a protein-protein interface between their malectin domains which forms a deep cleft lined by highly conserved aromatic and polar residues. Analysis of the glycosylation patterns of different CrRLK1Ls and their oligomeric states suggests that this cleft could resemble a binding site for a ligand required for receptor activation of CrRLK1Ls.
植物受精过程需要雄性花粉管和雌性生殖器官之间复杂的细胞间通讯。长春花受体激酶 1 样（CrRLK1L）家族的膜受体已被遗传证实参与了这一过程。本文分别报道了 CrRLK1Ls ANXUR1 和 ANXUR2 的晶体结构，分辨率分别为 1.48 和 1.1 Å。这些结构揭示了两个甘露糖结合酶样结构域通过短 β 发夹连接子连接的新颖排列方式，并由钙离子稳定。与相关动物和细菌糖结合模块的典型碳水化合物相互作用表面不同，植物 CrRLK1L 中不保守。与此一致的是，化学多样性的寡糖与 ANXUR1 和 HERCULES1 的结合不能被检测到。相反，CrRLK1L 在它们的甘露糖结构域之间进化出了一个蛋白-蛋白界面，形成了一个由高度保守的芳香族和极性残基排列的深裂缝。对不同 CrRLK1L 的糖基化模式及其寡聚状态的分析表明，这个裂缝可能类似于 CrRLK1L 受体激活所需配体的结合位点。
