Complex III of Electron Transport Chain: Difference between revisions

Complex III of the electron transport chain has a dimeric structure with each monomer containing as many as 11 subunits, but the structure shown to the right has 9. <ref>C.Lange,C.Hunte, Crystal Structure of The Yeast Cytochrome BC1 Complex with Its Bound Substrate Cytochrome C., Proc. Natl. Acad. Sci. USA, '''99''', 2800, 2002</ref> <ref>1KYO.pdb is being used to generate the images in the first applet.  The 'default scene' green link available in the first Jmol applet displays all the components of 1KYO.PDB which include all the peptides of the dimer structure along with Heavy Chain (Vh) of Fv-Fragment, Light Chain (Vl) of Fv-Fragment and Cytochrome C, Iso-1. Follow the link to OCA in the green table below the applet for additional information on the complete complex and the peptide components.</ref> (<scene name='Complex_III_of_Electron_Transport_Chain/Homodimer/3'>Reset initial scene.</scene>) <scene name='Complex_III_of_Electron_Transport_Chain/View_one_subunit/3'>Coloring one monomeric unit grey</scene> reveals this dimeric structure.  Notice that <font color='red'>one</font> of the peptides of each subunit invades the space of the other monomeric unit, and labels show the orientation of the complex within the inner mitochondrial membrane. <scene name='Complex_III_of_Electron_Transport_Chain/View_3_active_subunits/4'>Three of the subunits</scene> (colored green, blue and red) of each monomeric unit have a direct role in the passage of electrons in the respiratory chain. The grey peptides are not assigned a function in the current mechanism of redox reactions of Complex III, but they do have other catalytic activities and functions. For the most part, the two subunits of cytochrome b (colored green) are buried in the complex and have minimal exposure to the intermembrane space and matrix.  <font color='#0000CD'>Cytochrome c1 subunits</font> are positioned on top of cytochrome b and their outer surfaces are exposed to the intermembrane space.  They are held in place by helical tails that extend deep into the complex and the membrane. The <font color=red>Rieske subunits</font> are Fe/S proteins with three domains: membrane domain - long helical segment that extends into the membrane, hinge domain - short segment between the membrane and head domains, and head domain - contains the Fe/S center and occupies space in the other monomeric unit.  Therefore, as will be shown below, the Fe/S center interacts chemically with the cytochrome subunits which are located in the partner monomeric unit. <br><br>