The miluchondrial cytochrome bel complex was crystallized with the symmetry of spare group 14(1)22 and with unit tell dimensions of a = b = 153-4 A. c=597.7 A and one hi I monomer per asymmetric unit. Crystallographic phases were determined with the methods of multiple isomorphous replacement and anomalous scattering,; the\ were improved and extended to 2.9 A résolution lining density modification and partial structure information. The resulting electron density maps allowed identification of the complete subunits corel. core2. and cytochrome b. as well as subunit 6. subunit 7, and parts of cvtochrorne c 1 and of t he iron sulphur protein. The positions of the iron centers could be determined from anomalous scattering data. Crystallographic binding studies with the inhibitors myxothiazol and antimycin A helped to identify the quinorie binding sites and to assign the iron centers. There are 13 membrane-spanning helices per br 1 monomer. The complex forms dirners with close interactions between cytochromes b. core2 and subunit 6. The quinone binding sites are inside large cavities formed by the transmembrane helices of both monomers. The extramembrane domains of cytochrome c 1 and of the iron-sulphur protein are poorly ordered in the crystal; this could have functional significance. The subunits corel and core2, which are homologous to the subunits of mitochondrial matrix processing peptidase (MPP) form a rlosfly interacting heterodirner. A large cavity between corel and core2 could be arialoeous to the recognition site tor signal sequences in MPP.
|Original language||English (US)|
|State||Published - Dec 1 1997|
ASJC Scopus subject areas
- Molecular Biology