School of Pharmaceutical Sciences, Fujian Provincial Key Laboratory of Innovative Drug Target Research, Xiamen University, Xiamen, 361102, China.
NucMito Pharmaceuticals Co. Ltd., Xiamen, 361101, China.
Nat Commun. 2021 Oct 13;12(1):5989. doi: 10.1038/s41467-021-26295-8.
Liquid-liquid phase separation promotes the formation of membraneless condensates that mediate diverse cellular functions, including autophagy of misfolded proteins. However, how phase separation participates in autophagy of dysfunctional mitochondria (mitophagy) remains obscure. We previously discovered that nuclear receptor Nur77 (also called TR3, NGFI-B, or NR4A1) translocates from the nucleus to mitochondria to mediate celastrol-induced mitophagy through interaction with p62/SQSTM1. Here, we show that the ubiquitinated mitochondrial Nur77 forms membraneless condensates capable of sequestrating damaged mitochondria by interacting with the UBA domain of p62/SQSTM1. However, tethering clustered mitochondria to the autophagy machinery requires an additional interaction mediated by the N-terminal intrinsically disordered region (IDR) of Nur77 and the N-terminal PB1 domain of p62/SQSTM1, which confers Nur77-p62/SQSTM1 condensates with the magnitude and liquidity. Our results demonstrate how composite multivalent interaction between Nur77 and p62/SQSTM1 coordinates to sequester damaged mitochondria and to connect targeted cargo mitochondria for autophagy, providing mechanistic insight into mitophagy.
液-液相分离促进了无膜凝聚体的形成，这些凝聚体介导了多种细胞功能，包括错误折叠蛋白质的自噬。然而，相分离如何参与功能失调的线粒体（自噬）仍然不清楚。我们之前发现，核受体 Nur77（也称为 TR3、NGFI-B 或 NR4A1）通过与 p62/SQSTM1 相互作用，从细胞核易位到线粒体，从而介导 celastrol 诱导的线粒体自噬。在这里，我们表明，泛素化的线粒体 Nur77 形成无膜凝聚体，能够通过与 p62/SQSTM1 的 UBA 结构域相互作用来隔离受损的线粒体。然而，将聚集的线粒体固定到自噬机制需要 Nur77 和 p62/SQSTM1 的 N 端固有无序区（IDR）介导的额外相互作用，这赋予了 Nur77-p62/SQSTM1 凝聚体的大小和流动性。我们的结果表明，Nur77 和 p62/SQSTM1 之间的复合多价相互作用如何协调隔离受损的线粒体，并连接靶向货物线粒体进行自噬，为线粒体自噬提供了机制上的见解。
