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

• Published in: Nature plants Vol. 3; no. 12; pp. 973 - 982
• Main Authors: Ouyang, Min, Li, Xiaoyi, Zhao, Shun, Pu, Hua, Shen, Jianren, Adam, Zach, Clausen, Tim, Zhang, Lixin
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 01.12.2017; Nature Publishing Group
• Subjects: 631/449; 631/449/2675; Activity recognition; Arabidopsis; Biomedical and Life Sciences; Crystal structure; Cytokinins; High temperature; Homology; Life Sciences; Photodegradation; Plant Sciences; Protease; Proteinase; Proteolysis; Serine proteinase; Signal transduction; Substrates; Temperature requirements; Beijing China; China
• ISSN: 2055-0278; 2055-0278
• DOI: 10.1038/s41477-017-0060-2

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. The Deg/HtrA family of ATP-independent serine proteases functions in a wide range of regulatory pathways. Here, the crystal structure of Arabidopsis Deg9 shows a novel oligomeric assembly of this nuclear-localized protease, an interesting octamer.