Gaining mass: the structure of respiratory complex I - from bacterial towards mitochondria! versions

The 1 MDa, 45-subunit proton-pumping NADH-ubiquinone oxidoreductase (complex I) is the largest complex of the mitochondrial electron transport chain. The molecular mechanism of complex I is central to the metabolism of cells, but has yet to be fully characterized. The last two years have seen steady progress towards this goal with the first atomic-resolution structure of the entire bacterial complex I, a 5 angstrom cryo-electron microscopy map of bovine mitochondrial complex I and a similar to 3.8 angstrom resolution X-ray crystallographic study of mitochondrial complex I from yeast Yarrowia lipotytica. In this review we will discuss what we have learned from these studies and what remains to be elucidated.