Human mitochondrial complex I assembly: a dynamic and versatile process.

One can but admire the intricate way in which biomolecular structures are formed and cooperate to allow proper cellular function. A prominent example of such intricacy is the assembly of the five inner membrane embedded enzymatic complexes of the mitochondrial oxidative phosphorylation (OXPHOS) system, which involves the stepwise combination of >80 subunits and prosthetic groups encoded by both the mitochondrial and nuclear genomes. This review will focus on the assembly of the most complicated OXPHOS structure: complex I (NADH:ubiquinone oxidoreductase, EC 1.6.5.3). Recent studies into complex I assembly in human cells have resulted in several models elucidating a thus far enigmatic process. In this review, special attention will be given to the overlap between the various assembly models proposed in different organisms. Complex I being a complicated structure, its assembly must be prone to some form of coordination. This is where chaperone proteins come into play, some of which may relate complex I assembly to processes such as apoptosis and even immunity.