Biology Department, Brookhaven National Laboratory, Upton, NY, USA.
NSLS-II, Brookhaven National Laboratory, Upton, NY, USA.
Nat Commun. 2020 May 7;11(1):2249. doi: 10.1038/s41467-020-15830-8.
Plant metacaspases mediate programmed cell death in development, biotic and abiotic stresses, damage-induced immune response, and resistance to pathogen attack. Most metacaspases require Ca for their activation and substrate processing. However, the Ca-dependent activation mechanism remains elusive. Here we report the crystal structures of Metacaspase 4 from Arabidopsis thaliana (AtMC4) that modulates Ca-dependent, damage-induced plant immune defense. The AtMC4 structure exhibits an inhibitory conformation in which a large linker domain blocks activation and substrate access. In addition, the side chain of Lys225 in the linker domain blocks the active site by sitting directly between two catalytic residues. We show that the activation of AtMC4 and cleavage of its physiological substrate involve multiple cleavages in the linker domain upon activation by Ca. Our analysis provides insight into the Ca-dependent activation of AtMC4 and lays the basis for tuning its activity in response to stresses for engineering of more sustainable crops for food and biofuels.
植物的 metacaspases 参与发育、生物和非生物胁迫、损伤诱导的免疫反应以及对病原体攻击的抗性中的程序性细胞死亡。大多数 metacaspases 需要 Ca 才能激活并处理底物。然而，Ca 依赖性激活机制仍不清楚。在这里，我们报告了拟南芥（Arabidopsis thaliana）Metacaspase 4（AtMC4）的晶体结构，它调节 Ca 依赖性的、损伤诱导的植物免疫防御。AtMC4 结构呈现出抑制构象，其中一个大的连接子结构域阻止激活和底物进入。此外，连接子结构域中 Lys225 的侧链通过直接位于两个催化残基之间，从而阻断活性位点。我们表明，AtMC4 的激活和其生理底物的切割涉及在 Ca 激活后通过多个切割来完成连接子结构域的切割。我们的分析提供了对 AtMC4 的 Ca 依赖性激活的深入了解，并为响应胁迫来调节其活性以用于粮食和生物燃料的更可持续作物的工程设计奠定了基础。
