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The mitochondrial NME6 protein is enzymatically inactive but interacts with RCC1L (WBSCR16) in the matrix space

Introduction: The nucleoside diphosphate kinases (NDPK/NME/Nm23) are a family of enzymes catalyzing the transfer of gamma phosphate from NTPs to NDPs. The family consists of 10 members in human. The discovery of metastasis suppressor activity for NME1 raised considerable scientific interest. Studies of cytosolic NME1-2 and mitochondrial NME3-4 revealed the enzymatic activity mechanism, which depends on the phosphorylation of a specific histidine in the catalytic site, and requires NMEs to assemble as hexamers. We focused our research on the barely explored mitochondrial NME6 protein1. Material & Methods: We used immunofluorescence and live cells imaging to confirm NME6 mitochondrial localization, and refined it using mitochondrial subfractionation. NDP kinase activity assay and immunoblotting with anti-phosphohistidine antibody were used to explore enzymatic properties. Standard immunoprecipitations were used to reveal interacting partners. Results: We confirmed the mitochondrial localization, and exposed new evidence for NME6 as a matrix facing protein. We showed that NME6 lacks NDP kinase activity, linked to the lack of histidine phosphorylation and inability to oligomerize. Finally, we showed that NME6 interacts with RCC1L, a matrix facing protein affecting mitochondrial ribosome biogenesis2. Conclusion: Our research brings fundamental knowledge on mitochondrial NME6 protein, paving the way for understanding its function. 1. Tsuiki H, Nitta M, Furuya A, et al (2000) A novel human nucleoside diphosphate (NDP) kinase, Nm23-H6, localizes in mitochondria and affects cytokinesis. J Cell Biochem 76:254–269. https://doi.org/10.1002/(SICI)1097- 4644(20000201)76:2<254::AID-JCB9>3.0.CO ; 2-G 2. Reyes A, Favia P, Vidoni S, et al (2020) RCC1L (WBSCR16) isoforms coordinate mitochondrial ribosome assembly through their interaction with GTPases. PLOS Genet 16:e1008923. https://doi.org/10.1371/journal.pgen.1008923

NME6, RCC1L, WBSCR16, Mitochondria

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