A N Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow, Russia.
Cell Death Differ. 2011 Aug;18(8):1289-97. doi: 10.1038/cdd.2011.49. Epub 2011 May 6.
Activities displaying caspase cleavage specificity have been well documented in various plant programmed cell death (PCD) models. However, plant genome analyses have not revealed clear orthologues of caspase genes, indicating that enzyme(s) structurally unrelated yet possessing caspase specificity have functions in plant PCD. Here, we review recent data showing that some caspase-like activities are attributable to the plant subtilisin-like proteases, saspases and phytaspases. These proteases hydrolyze a range of tetrapeptide caspase substrates following the aspartate residue. Data obtained with saspases implicate them in the proteolytic degradation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) during biotic and abiotic PCD, whereas phytaspase overproducing and silenced transgenics provide evidence that phytaspase regulates PCD during both abiotic (oxidative and osmotic stresses) and biotic (virus infection) insults. Like caspases, phytaspases and saspases are synthesized as proenzymes, which are autocatalytically processed to generate a mature enzyme. However, unlike caspases, phytaspases and saspases appear to be constitutively processed and secreted from healthy plant cells into the intercellular space. Apoplastic localization presumably prevents enzyme-mediated protein fragmentation in the absence of PCD. In response to death-inducing stimuli, phytaspase has been shown to re-localize to the cell interior. Thus, plant PCD-related proteases display both common (D-specific protein fragmentation during PCD) and distinct (enzyme structure and activity regulation) features with animal PCD-related proteases.
在各种植物程序性细胞死亡（PCD）模型中，已充分证明具有半胱天冬酶切割特异性的活性。然而，植物基因组分析并未揭示半胱天冬酶基因的明确同源物，这表明结构上不相关但具有半胱天冬酶特异性的酶在植物 PCD 中具有功能。在这里，我们回顾了最近的数据，这些数据表明，某些半胱天冬酶样活性归因于植物枯草杆菌蛋白酶样蛋白酶、saspases 和 phytaspases。这些蛋白酶在天冬氨酸残基后水解一系列四肽半胱天冬酶底物。saspases 的数据表明它们参与生物和非生物 PCD 期间核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）的蛋白水解降解，而过度表达和沉默的 phytaspase 转基因提供的证据表明 phytaspase 调节非生物（氧化和渗透胁迫）和生物（病毒感染）胁迫期间的 PCD。与半胱天冬酶一样，phytaspases 和 saspases 作为前酶合成，它们通过自催化处理生成成熟酶。然而，与半胱天冬酶不同，phytaspases 和 saspases 似乎在健康植物细胞中被持续加工并分泌到细胞外空间。质外体定位大概可以防止在没有 PCD 的情况下酶介导的蛋白质片段化。在诱导死亡的刺激下，已经表明 phytaspase 重新定位于细胞内部。因此，与动物 PCD 相关的蛋白酶具有共同的特征（PCD 期间 D-特异性蛋白片段化）和独特的特征（酶结构和活性调节）。
