We have crystallized complex III (the cytochroMo bc1 complex) in hexagonal(P6522) crystals from cow and rabbit, monoclintc(P2 1) crystals from cow, and orthorhombic(P212 121) crystals from chicken. The chicken crystals diffract to 3.0 Å, the hexagonal rabbit to 3.5 Å, and both cow crystals to 3.75 Å. The orthorhornbic and monoclinic crystals each have a dimer of the bc1 complex in the asymmetric unit. This allows us to address questions about the symmotry of the dimeric bei complex. We will present the structures of the three redox-center-bearing subunits and the molecular interactions between them. There is a significant difference in the ironsulfur position in the different crystal forms. We will discuss two nypothesees concerning functioning of the ironsulfur protein. In one hypothesis all the redox centers remain fixed during the catalytic cycles, and participate in relatively long-distance (∼20 A) electron transfer events. In the other hypothesis the ironsulfur protein oscillates between one position which puts the ironsulfur cluster close to the Qo site and another position which puts it close to cytochrome c1, and electron transfer occurs over shorter distances.
|Original language||English (US)|
|State||Published - 1997|