NADH-dehydrogenase (ubiquinone) Fe-S protein 7，簡稱NDUFS7，為粒線體酵素複合體I中由細胞核基因所表現的核心蛋白，此蛋白具有一個 [4Fe-4S] 的鐵硫中心，可協助氧化磷酸化中電子的傳遞並伴隨細胞能量的產生，臨床上NDUFS7的缺失已經被發現與一些神經退化疾病例如Leigh症候群及躁鬱症相關。在近幾年的研究指出，由粒線體酵素複合體I~V所形成更大的複合體，有助維持結構穩定性及提升電子傳遞的效率。在本研究中使用核酸干擾 (RNAi) 技術抑制T-REx293細胞中NDUFS7的表現，且分析在NDUFS7缺失的情況下對細胞功能的影響。結果顯示在NDUFS7表現量減少的情況下會導致細胞耗氧率、粒線體膜電位、ATP合成量皆有下降以及酵素複合體I的活性降低。此外，對細胞有害的自由基及活性氧化物在粒線體中則有明顯的增加。另一方面，藉由HrCNE的分析中發現缺少NDUFS7和酵素複合體I中另一個核心蛋白NDUFV2皆會影響酵素複合體I的形成，連帶導致酵素複合體III或IV的減少。同時NDUFS7也參與維持由酵素複合體I、III、IV所組成的超複合體結構。這些結果都表示NDUFS7不但在電子傳遞的過程扮演著不可或缺的角色並且影響著這些酵素複合體及超複合體的組合。

NADH-dehydrogenase (ubiquinone) Fe-S protein 7 (NDUFS7), a highly conserved protein encoded by the nuclear DNA, is one of the core subunits in the mitochondrial NADH-coenzyme Q oxidoreductase (Complex I). It contains a tetranuclear iron-sulfur cluster N2 that assists electron transfer and serves as the final electron donor for ubiquinone and thus contributes to energy generation in the oxidative phosphorylation (OXPHOS) system. Mutations in NDUFS7 have been reported in patients suffering from neurodegenerative diseases such as Leigh syndrome and might also been assoicated with bipolar disorder. In addition to being present as an individual complex, the assembly of component OXPHOS complexes (Complex I~V) into several larger supercomplexes is considered to have functional significance not only for maintaining the stability of complexes but also for increasing the efficiency of electron transfer. In this study, we applied the RNA interference technique to suppress NDUFS7 expression in T-REx293 cells and then analyzed the obtained knockdown cell lines O10 and U21 with a series of functional assays. Our results showed that knockdown of NDUFS7 caused a significant decrease in the cellular oxygen consumption rate, mitochondrial membrane potential, ATP generation and Complex I activity. In addition, the amount of harmful reactive oxygen species was apparently increased in mitochondria. On the other hand, by conducting the high resolution clear native electrophoresis (HrCNE) analyses, we found that the deficiency of NDUFS7 or NDUFV2 influenced individual complex assembly and reduced the stability of Complex I subunits. By applying a milder condition for extraction of protein complexes from the mitochondrial samples, we also found that the deficiency of NDUFS7 could hamper supercomplex formation. Based on these findings, we conclude that NDUFS7 plays an indispensable role in maintaining the functions of electron transport chain and the assembly of individual Complex I, III, and IV and the supercomplex.

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