Abstract：
Mutations in FBXO7 have been discovered to be associated with an atypical parkinsonism. We report here a new homozygous missense mutation in a paediatric patient that causes an L250P substitution in the dimerisation domain of Fbxo7. This alteration selectively ablates the Fbxo7-PI31 interaction and causes a significant reduction in Fbxo7 and PI31 levels in patient cells. Consistent with their association with proteasomes, patient fibroblasts have reduced proteasome activity and proteasome subunits. We also show PI31 interacts with the MiD49/51 fission adaptor proteins, and unexpectedly, PI31 acts to facilitate SCFFbxo7-mediated ubiquitination of MiD49. The L250P mutation reduces the SCFFbxo7 ligase-mediated ubiquitination of a subset of its known substrates. Although MiD49/51 expression was reduced in patient cells, there was no effect on the mitochondrial network. However, patient cells show reduced levels of mitochondrial function and mitophagy, higher levels of ROS and are less viable under stress. Our study demonstrates that Fbxo7 and PI31 regulate proteasomes and mitochondria and reveals a new function for PI31 in enhancing the SCFFbxo7 E3 ubiquitin ligase activity.
摘要：
已发现FBXO7中的突变与非典型帕金森病有关。我们在这里报告了儿科患者中的一种新的纯合错义突变，该突变导致Fbxo7的二聚化结构域中的L250P取代。这种改变选择性地消除Fbxo7-PI31相互作用,并引起患者细胞中Fbxo7和PI31水平的显著降低。与它们与蛋白酶体的联系一致，患者成纤维细胞的蛋白酶体活性和蛋白酶体亚基降低。我们还显示PI31与MiD49/51裂变衔接蛋白相互作用，出乎意料的是，PI31有助于SCFFbxo7介导的MiD49的泛素化。L250P突变减少了SCFFbxo7连接酶介导的其已知底物子集的泛素化。尽管MiD49/51在患者细胞中的表达降低,对线粒体网络没有影响。然而,患者细胞显示线粒体功能和线粒体自噬水平降低，ROS水平较高，在压力下活力较低。我们的研究表明，Fbxo7和PI31调节蛋白酶体和线粒体，并揭示了PI31在增强SCFFbxo7E3泛素连接酶活性方面的新功能。
