西湖大学柴继杰等研究人员合作揭示植物NLR的寡聚化介导的自抑制和辅因子结合。2024年6月12日，国际知名学术期刊《自然》在线发表了这一成果。

研究人员表示，核苷酸结合富亮氨酸重复（NLR）蛋白通过识别病原体效应物在植物免疫中发挥着关键作用。保持平衡的免疫反应至关重要，因为过量的NLR表达会导致意外的自身免疫。与大多数NLR不同，植物细胞死亡所需的NLR 2（NRC2）属于一个小的NLR类别，其特点是组成型高表达而无自我激活。NRC2的自抑制和激活机制尚不清楚。

研究人员发现番茄（Solanum lycopersicum）NRC2（SlNRC2）会形成二聚体和四聚体，并在浓度升高时形成高阶寡聚体。冷冻电镜（cryo-EM）显示，SlNRC2在这些寡聚体中处于非活性构象。二聚化和寡聚化不仅能稳定非活性状态，还能阻止SlNRC2组装成活性形式。

二聚体或二聚体间界面的突变会增强病原体诱导的烟草细胞死亡和免疫。cryo-EM结构意外地发现了结合到SlNRC2 C端LRR结构域内表面的肌醇六磷酸（IP₆）或肌醇五磷酸（IP₅），质谱分析证实了这一点。IP结合位点的突变损害了SlNRC2与磷酸肌醇的结合以及病原体诱导的SlNRC2介导的烟草细胞死亡。总之，该研究揭示了一种新的NLR激活负调控机制，并表明肌醇磷酸盐是NRC的辅助因子。

附：英文原文

Title: Oligomerization-mediated autoinhibition and cofactor binding of a plant NLR

Author: Ma, Shoucai, An, Chunpeng, Lawson, Aaron W., Cao, Yu, Sun, Yue, Tan, Eddie Yong Jun, Pan, Jinheng, Jirschitzka, Jan, Kmmel, Florian, Mukhi, Nitika, Han, Zhifu, Feng, Shan, Wu, Bin, Schulze-Lefert, Paul, Chai, Jijie

Issue&Volume: 2024-06-12

Abstract: Nucleotide-binding leucine-rich repeat (NLR) proteins have a pivotal role in plant immunity by recognizing pathogen effectors1,2. Maintaining a balanced immune response is crucial, as excessive NLR expression can lead to unintended autoimmunity3,4. Unlike most NLRs, plant NLR required for cell death 2 (NRC2) belongs to a small NLR group characterized by constitutively high expression without self-activation5. The mechanisms underlying NRC2 autoinhibition and activation are not yet understood. Here we show that Solanum lycopersicum (tomato) NRC2 (SlNRC2) forms dimers and tetramers, and higher-order oligomers at elevated concentrations. Cryo-electron microscopy (cryo-EM) reveals an inactive conformation of SlNRC2 within these oligomers. Dimerization and oligomerization not only stabilize the inactive state but also sequester SlNRC2 from assembling into an active form. Mutations at the dimeric or inter-dimeric interfaces enhance pathogen-induced cell death and immunity in Nicotiana (N.) benthamiana. The cryo-EM structures unexpectedly reveal inositol hexakisphosphate (IP6) or pentakisphosphate (IP5) bound to the inner surface of SlNRC2’s C-terminal LRR domain as confirmed by mass spectrometry. Mutations at the IP-binding site impair inositol phosphate binding of SlNRC2 and pathogen-induced SlNRC2-mediated cell death in N. benthamiana. Together, our study unveils a novel negative regulatory mechanism of NLR activation and suggests inositol phosphates as cofactors of NRCs.

DOI: 10.1038/s41586-024-07668-7

Source: https://www.nature.com/articles/s41586-024-07668-7