Open conformation of a flavocytochrome c(3) fumarate reductase

Fumarate reductases and succinate dehydrogenases play central roles in the metabolism of eukaryotic and prokaryotic cells. A recent medium resolution structure of the Escherichia coil fumarate reductase (Frd) has revealed the overall organization of the membrane-bound complex. Here we present the fi rst high resolution X-ray crystal structure of a water-soluble bacterial fu marate reductase in an open conformation. This structure reveals a mobile d omain that modulates substrate access to the active site and provides new i nsights into the mechanism of this widespread and important family of FAD-c ontaining respiratory proteins.