ABSTRACT
Mitochondria, originated from the last eukaryotic common ancestor by endosymbiosis, are semi-autonomous double-membrane organelles. The oxidative phosphorylation system consists of five complexes that are coordinately encoded by the nuclear and mitochondrial genomes, and establishes the electron transport chain in the mitochondrial inner membrane, concurrently generating ATP using the proton gradient. The proton-pumping Complex I (NADH:ubiquinone oxidoreductase) is the first, large stand most complicated enzyme required in this process. Complex I is an L-shaped multimeric enzyme harbouring over 40 subunits, one FMN molecule and eight Fe-S clusters. In recent years, biochemical, genetic, proteomic and crysta-structure analyses of Complex I in several model systems have provided valuable insights into its function and biogenesis. This review summarizes our current understanding of Complex I structural modules, assembly pathway and factors, discusses their similarities and distinctions between animals and plants, as well as the evolution of Complex I. And we proposes some potentially important but yet unsolved questions of Complex I. Therefore, this review provides a relevant reference for further comprehensively deepening the function and evolution of mitochondrial Complex I.