Protein import into mitochondria is a highly regulated process, yet how cells clear mitochondria undergoing dysfunctional protein import remains poorly characterized. Here we showed that mitochondrial protein import stress (MPIS) triggers localized LC3 lipidation. This arm of the mitophagy pathway occurs through the Nod-like receptor (NLR) protein NLRX1 while, surprisingly, without the engagement of the canonical mitophagy protein PINK1. Mitochondrial depolarization, which itself induces MPIS, also required NLRX1 for LC3 lipidation. While normally targeted to the mitochondrial matrix, cytosol-retained NLRX1 recruited RRBP1, a ribosome-binding transmembrane protein of the endoplasmic reticulum, which relocated to the mitochondrial vicinity during MPIS, and the NLRX1/RRBP1 complex in turn controlled the recruitment and lipidation of LC3. Furthermore, NLRX1 controlled skeletal muscle mitophagy in vivo and regulated endurance capacity during exercise. Thus, localization and lipidation of LC3 at the site of mitophagosome formation is a regulated step of mitophagy controlled by NLRX1/RRBP1 in response to MPIS.

蛋白质输入线粒体是一个高度调节的过程，但细胞如何清除经历功能失调的蛋白质输入的线粒体仍然缺乏特征。在这里，我们发现线粒体蛋白输入应激 (MPIS) 触发了局部 LC3 脂化。线粒体自噬通路的这一臂通过 Nod 样受体 (NLR) 蛋白 NLRX1 发生，而令人惊讶的是，没有经典线粒体自噬蛋白 PINK1 的参与。本身诱导 MPIS 的线粒体去极化也需要 NLRX1 来进行 LC3 脂化。虽然通常靶向线粒体基质，但细胞质保留的 NLRX1 募集 RRBP1，一种内质网的核糖体结合跨膜蛋白，在 MPIS 期间重新定位到线粒体附近，而 NLRX1/RRBP1 复合物反过来控制 LC3 的募集和脂化. 此外，体内和运动期间调节的耐力能力。因此，LC3 在线粒体形成部位的定位和脂化是响应 MPIS 的 NLRX1/RRBP1 控制的线粒体自噬的调节步骤。