Signalling and Structural Biology Laboratory, Francis Crick Institute, NW1 1AT London, UK.
Structural Biology Science Technology Platform, Francis Crick Institute, NW1 1AT London, UK.
Structure. 2021 Jul 1;29(7):694-708.e7. doi: 10.1016/j.str.2020.12.012. Epub 2021 Jan 22.
RET receptor tyrosine kinase plays vital developmental and neuroprotective roles in metazoans. GDNF family ligands (GFLs) when bound to cognate GFRα co-receptors recognize and activate RET stimulating its cytoplasmic kinase function. The principles for RET ligand-co-receptor recognition are incompletely understood. Here, we report a crystal structure of the cadherin-like module (CLD1-4) from zebrafish RET revealing interdomain flexibility between CLD2 and CLD3. Comparison with a cryo-electron microscopy structure of a ligand-engaged zebrafish RET-GDNF-GFRα1a complex indicates conformational changes within a clade-specific CLD3 loop adjacent to the co-receptor. Our observations indicate that RET is a molecular clamp with a flexible calcium-dependent arm that adapts to different GFRα co-receptors, while its rigid arm recognizes a GFL dimer to align both membrane-proximal cysteine-rich domains. We also visualize linear arrays of RET-GDNF-GFRα1a suggesting that a conserved contact stabilizes higher-order species. Our study reveals that ligand-co-receptor recognition by RET involves both receptor plasticity and strict spacing of receptor dimers by GFL ligands.
RET 受体酪氨酸激酶在后生动物中发挥着至关重要的发育和神经保护作用。GDNF 家族配体（GFL）与同源 GFRα 共受体结合后，识别并激活 RET，刺激其细胞质激酶功能。RET 配体-共受体识别的原则尚不完全清楚。在这里，我们报告了来自斑马鱼 RET 的钙粘蛋白样结构域（CLD1-4）的晶体结构，揭示了 CLD2 和 CLD3 之间的结构域间灵活性。与配体结合的斑马鱼 RET-GDNF-GFRα1a 复合物的冷冻电镜结构的比较表明，与 co-receptor 相邻的特定于类群的 CLD3 环内发生构象变化。我们的观察表明，RET 是一种分子夹，具有灵活的钙依赖性臂，可适应不同的 GFRα 共受体，而其刚性臂识别 GFL 二聚体以对齐两个膜近端富含半胱氨酸的结构域。我们还可视化了 RET-GDNF-GFRα1a 的线性阵列，表明保守的接触稳定了更高阶的物种。我们的研究表明，RET 的配体-共受体识别涉及受体的可塑性和 GFL 配体严格间隔的受体二聚体。
