| Summary: | 碩士 === 國立清華大學 === 分子醫學研究所 === 101 === Human NADH dehydrogenase (ubiquinone) Fe-S protein 7 (NDUFS7) is one of the most conserved core subunits of mitochondrial complex I. NDUFS7 has a bound iron-sulfur cluster N2 (tetranuclear) which is the terminal redox center in the electron transport chain (ETC) of complex I. NDUFS7 protein is encoded by the nuclear genome and is incorporated in the peripheral segment of complex I. Most mitochondrial matrix proteins are synthesized in the cytosol and imported into mitochondria by mitochondrial targeting sequences (MTSs).
We previously defined the N terminus of the first 60 amino acids of NDUFS7 is an effective MTS. We also identified that there is a nuclear localization signal (NLS) and a nuclear export signal (NES) located in the C-terminus of NDUFS7. Sumoylation has been recognized to play an important role in protein nucleocytoplasmic transportation. Small ubiquitin-related modifiers (SUMOs) could be conjugated to target proteins by E1 (SAE1/SAE2), E2 (UBC9) and E3 enzymes after translation. Using sequence predication software, NDUFS7 protein was found to have several potential sumoylation sites. In this study, we co-transfected plasmids expressed NDUFS7, SUMO-1 and UBC9 into HEK293 cells, and detected the conjugation of NDUFS7 with SUMO-1 by western blotting with different antibodies. The results indicated that NDUFS7 could indeed be sumoylated at the current experimental conditions in vivo. To confirm these findings, SUMO-specific protease (SENP) was co-expressed with NDUFS7, SUMO-1 and UBC9 proteins in some experiments. The results showed that overexpression of SENP could reduce the level of NDUFS7 and SUMO-1 interaction. These results suggested that NDUFS7 can be sumoylated by SUMO-1 in cells. In addition, we also identified one of the sumoylation sites of NDUFS7 to be Lys 202, which is consistent with the consensus sumoylation motif and is required for NDUFS7 protein stability. Further studies are needed and on the way to investigate the functional detail of NDUFS7 sumoylation.
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