A.N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia.
EMBO J. 2010 Mar 17;29(6):1149-61. doi: 10.1038/emboj.2010.1. Epub 2010 Jan 28.
Caspases are cysteine-dependent proteases and are important components of animal apoptosis. They introduce specific breaks after aspartate residues in a number of cellular proteins mediating programmed cell death (PCD). Plants encode only distant homologues of caspases, the metacaspases that are involved in PCD, but do not possess caspase-specific proteolytic activity. Nevertheless, plants do display caspase-like activities indicating that enzymes structurally distinct from classical caspases may operate as caspase-like proteases. Here, we report the identification and characterisation of a novel PCD-related subtilisin-like protease from tobacco and rice named phytaspase (plant aspartate-specific protease) that possesses caspase specificity distinct from that of other known caspase-like proteases. We provide evidence that phytaspase is synthesised as a proenzyme, which is autocatalytically processed to generate the mature enzyme. Overexpression and silencing of the phytaspase gene showed that phytaspase is essential for PCD-related responses to tobacco mosaic virus and abiotic stresses. Phytaspase is constitutively secreted into the apoplast before PCD, but unexpectedly is re-imported into the cell during PCD providing insights into how phytaspase operates.
半胱氨酸依赖性蛋白酶 Caspases 是动物细胞凋亡的重要组成部分。它们在许多细胞蛋白中引入特定的断裂，这些蛋白介导程序性细胞死亡（PCD）。植物只编码与 Caspases 有远亲关系的 Metacaspases，这些 Metacaspases 参与 PCD，但不具有 Caspase 特异性的蛋白水解活性。然而，植物确实表现出 Caspase 样活性，这表明结构上不同于经典 Caspases 的酶可能作为 Caspase 样蛋白酶发挥作用。在这里，我们报道了一种新型的与 PCD 相关的烟草和水稻枯草杆菌样蛋白酶的鉴定和特征，命名为 phytaspase（植物天冬氨酸特异性蛋白酶），它具有不同于其他已知 Caspase 样蛋白酶的 Caspase 特异性。我们提供的证据表明，phytaspase 作为前酶合成，该前酶通过自身催化加工生成成熟酶。phytaspase 基因的过表达和沉默表明，phytaspase 对于烟草花叶病毒和非生物胁迫引起的 PCD 相关反应是必需的。phytaspase 在 PCD 之前持续分泌到质外体，但出乎意料的是，在 PCD 期间被重新导入细胞，这为 phytaspase 的作用方式提供了新的见解。
