本文2017年11月27日在线发表于Nat ure Plants，原题目为：

The crystal structure of Deg9 reveals a novel octameric-type HtrA protease

HtrA蛋白酶（也称为Deg蛋白酶）通过调节蛋白质质量和数量在不同的生物体中起重要作用。16个拟南芥同源物中的一个，Deg9定位于细胞核，它通过降解ARR4来调节细胞分裂素和光介导的信号。为了揭示Deg9蛋白水解活性的结构特征，我们确定了它的晶体结构。与HtrA建立的三元构建模块不同，Deg9展示了由两个具有不同构象的四聚体环组成的新八聚体结构。基于结构体系，我们构建了Deg9的几种突变体，确定了它们的结构并测试了它们对ARR4的蛋白水解活性。结构和生物化学分析的结果使我们能够建立Deg9底物识别和活性调控新机制的模型。在这个模型中，一个四聚体的蛋白酶激活通过蛋白酶结构域的整体重新定向来调节，以打开相反（无活性）四聚体中底物的入口。这项研究为了解植物蛋白酶如何调节核信号成分的水平提供了结构基础。

The high temperature requirement A (HtrA) proteases (also termed Deg proteases) play important roles in diverse organisms by regulating protein quality and quantity. One of the 16 Arabidopsis homologs, Deg9, is located in the nucleus where it modulates cytokinin- and light-mediated signalling via degrading the ARABIDOPSIS RESPONSE REGULATOR 4 (ARR4). To uncover the structural features underlying the proteolytic activity of Deg9, we determined its crystal structure. Unlike the well-established trimeric building block of HtrAs, Deg9 displays a novel octameric structure consisting of two tetrameric rings that have distinct conformations. Based on the structural architecture, we generated several mutant variants of Deg9, determined their structure and tested their proteolytic activity towards ARR4. The results of the structural and biochemical analyses allowed us to propose a model for a novel mechanism of substrate recognition and activity regulation of Deg9. In this model, protease activation of one tetramer is mediated by en-bloc reorientation of the protease domains to open an entrance for the substrate in the opposite (inactive) tetramer. This study provides the structural basis for understanding how the levels of nuclear signal components are regulated by a plant protease.

[例句]Proteolysis The hydrolysis of proteins into their amino acid. Enzymes that catalyze this are proteases or proteolytic enzymes.

蛋白质水解：指蛋白质被水解为氨基酸。催化的酶为蛋白酶或蛋白水解酶。