The Sainsbury Laboratory, University of East Anglia, Norwich Research Park, Norwich, UK.
Bioimaging Facility, John Innes Centre, Norwich Research Park, Norwich, UK.
Sci Adv. 2024 Nov 8;10(45):eadr2594. doi: 10.1126/sciadv.adr2594. Epub 2024 Nov 6.
NRCs are essential helper NLR (nucleotide-binding domain and leucine-rich repeat) proteins that execute immune responses triggered by sensor NLRs. The resting state of NbNRC2 was recently shown to be a homodimer, but the sensor-activated state remains unclear. Using cryo-EM, we determined the structure of sensor-activated NbNRC2, which forms a hexameric inflammasome-like resistosome. Mutagenesis of the oligomerization interface abolished immune signaling, confirming the functional significance of the NbNRC2 resistosome. Comparative structural analyses between the resting state homodimer and sensor-activated homohexamer revealed substantial rearrangements, providing insights into NLR activation mechanisms. Furthermore, structural comparisons between NbNRC2 hexamer and previously reported CC-NLR pentameric assemblies revealed features allowing an additional protomer integration. Using the NbNRC2 hexamer structure, we assessed the recently released AlphaFold 3 for predicting activated CC-NLR oligomers, revealing high-confidence modeling of NbNRC2 and other CC-NLR amino-terminal α1 helices, a region proven difficult to resolve structurally. Overall, our work sheds light on NLR activation mechanisms and expands understanding of NLR structural diversity.
NRCs 是一种重要的辅助 NLR（核苷酸结合域和富含亮氨酸重复序列）蛋白，可执行传感器 NLR 触发的免疫反应。最近发现 NbNRC2 的静息状态是同源二聚体，但传感器激活状态仍不清楚。我们使用 cryo-EM 确定了传感器激活的 NbNRC2 的结构，它形成了六聚体炎性小体样抵抗体。寡聚化界面的突变消除了免疫信号，证实了 NbNRC2 抵抗体的功能意义。在静息状态同源二聚体和传感器激活同源六聚体之间进行的比较结构分析显示出大量的重排，为 NLR 激活机制提供了深入了解。此外，NbNRC2 六聚体和以前报道的 CC-NLR 五聚体组装体之间的结构比较揭示了允许额外原体整合的特征。我们使用 NbNRC2 六聚体结构评估了最近发布的 AlphaFold 3 对预测激活的 CC-NLR 寡聚体的能力，揭示了 NbNRC2 和其他 CC-NLR N 端 α1 螺旋的高置信度建模，该区域在结构上难以解决。总体而言，我们的工作阐明了 NLR 激活机制，并扩展了对 NLR 结构多样性的理解。
