Complex III of Electron Transport Chain

UNDER CONSTRUCTION

IntroductionIntroduction

spinqualitylabelsall models PDB ID 1kyo Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image
1kyo, resolution 2.97Å ()
Ligands:	, ,
Non-Standard Residues:
Activity:	Ubiquinol--cytochrome-c reductase, with EC number 1.10.2.2
Related:	1ezv, 1kb9
Structural annotation: Resources: CATH : 1Kyoa02, 1Kyoa01, 1Kyob02, 1Kyob01, 1Kyoc00, 1Kyod01, 1Kyod02, 1Kyoe01, 1Kyoe02, 1Kyof00, 1Kyog00, 1Kyoh00, 1Kyoi00, 1Kyoj00, 1Kyok00, 1Kyol02, 1Kyol01, 1Kyom02, 1Kyom01, 1Kyon00, 1Kyoo01, 1Kyoo02, 1Kyop01, 1Kyop02, 1Kyoq00, 1Kyor00, 1Kyos00, 1Kyot00, 1Kyou00, 1Kyov00, 1Kyow00 InterPro : Ipr011237, Ipr001431, Ipr007863, Ipr011249, Ipr011765, Ipr005798, Ipr005797, Ipr002326, Ipr009056, Ipr004192, Ipr006317, Ipr005806, Ipr014349, Ipr005805, Ipr003422, Ipr003197, Ipr004205, Ipr008027, Ipr003088, Ipr012125, Ipr002327 Pfam : PF00675, PF05193, PF00032, PF00033, PF02167, PF02921, PF00355, PF02271, PF02939, PF05365, PF00034 SCOP : d1kyoa2, d1kyoa1, d1kyob2, d1kyob1, d1kyoc2, d1kyoc3, d1kyod2, d1kyod1, d1kyoe2, d1kyoe1, d1kyof_, d1kyog_, d1kyoh_, d1kyoi_, d1kyol1, d1kyol2, d1kyom2, d1kyom1, d1kyon2, d1kyon3, d1kyoo2, d1kyoo1, d1kyop1, d1kyop2, d1kyoq_, d1kyor_, d1kyos_, d1kyot_, d1kyow_ UniProt : P07256, P07257, P00163, P07143, P08067, P00127, P00128, P08525, P22289, P00044
Functional annotation: Cellular component: mitochondrial respiratory chain mitochondrion membrane mitochondrial respiratory chain complex III integral to membrane mitochondrial inner membrane mitochondrial envelope mitochondrial intermembrane space Biological process: aerobic respiration electron transport proteolysis transport mitochondrial electron transport, ubiquinol to cytochrome c oxidative phosphorylation cytochrome bc(1) complex assembly iron-sulfur cluster assembly Molecular function: zinc ion binding protein binding metalloendopeptidase activity ubiquinol-cytochrome-c reductase activity iron ion binding metal ion binding electron transporter, transferring electrons within CoQH2-cytochrome c reductase complex activity oxidoreductase activity heme binding electron carrier activity iron-sulfur cluster binding 2 iron, 2 sulfur cluster binding
Evolutionary conservation: Toggle Conservation Colors: Rows = identical sequences: Further Information: Caveats, Explanation, Complete Results at ConSurfDB
Resources:	FirstGlance, OCA, PDBsum, RCSB
Coordinates:	save as pdb, mmCIF, xml

Complex III of the electron transport chain contains as many as 11 subunits per monomer. The structure shown to the right has 9. (The 'initial scene' green link available in the Jmol applet shows the dimer structure along with Heavy Chain (Vh) Of Fv-Fragment, Light Chain (Vl) Of Fv-Fragment and Cytochrome C, Iso-1 all of which are a part of 1KYO.PDB. The link to OCA in the green box below contains additional information on the complete complex and the individual peptide components.) of the complex within the inner mitochondrial membrane with labels. reveals that one of the peptides of each subunit invades the space of the other subunit. of each monomeric unit have a direct role in the passage of electrons in the respiratory chain. The subunits that are colored are active in the electron transport chain. The grey peptides have other catalytic activities and functions, and the interior spaces which are created by the positions of the other subunits have a role in the movement of the substrates from one active site to another active site within the complex. The two subunits of cytochrome b (colored green) for the most part are buried in the complex and have minimal exposure to the intermembrane space and matrix. Cytochrome c1 subunits 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 membrane. The Rieske subunits are Fe/S proteins with three domains: membrane domain (long helical segment that extends into the membrane), head domain which contains the Fe/S center and hinge domain (short segment between the other two).

Structure of three active componentsStructure of three active components

Each cytochrome b contains. Identify each of the hemes by hovering the curser over an atom of the heme. Hem 501 and Hem 502 are in one cytochrome b, and Hem 521 and Hem 522 are in the other one. The two hemes in each cytochrome b are in different environments and therefore have different properties, e.g. reduction potential. Hemes 501 & 521 have a lower potential than the other two and are called b_L for low potential, and the other two are called b_H for high potential. Each of the cytochrome b's have two binding sites for substrate. Ubiquinol binds at one of the sites, Q_P, and the inhibitor stigmatellin also binds at this site in both cytochrome b's (stigmatellin seen in the applet below)(), and the site is adjacent to the b_L heme. The other site, Q_N, binds ubiquinone, and outlines the site which is adjacent to the b_H heme. antimycin A.

spinqualitylabelsall models PDB ID 1kyo Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

Each cytochrome c1 contains . Viewing as it would be seen from the intermembrane space, there is an opening in the center of the dimeric structure through which one can see the gray hemes of the cyto b's. Also seen in this view is the gray heme embedded in each of the cyto c1's showing that the heme is located in a crevice which is open to the intermembrane space and to the (heme oxygens are seen). These openings of the crevice permits the cyto c1 heme to make contact with the Rieske protein and with cytochrome c when it binds to the . There are which attrack the complementary positive charges on cytochrome c, a basic protein. (colored cyan) bound to one cyto c1 showing that the hemes of the two cytochromes are in close contact. The seen through transparent spacefill.

is in the head of the Rieske protein. Each of the Fe/S centers is complexed with . As a result of bending at the the head can be in one of three possible positions. Here the Fe/S head is in the so called , because a His of the Fe/S/His complex is in contact with the ubiquinol bound at the Q_P site of cyto b. Of course in this model, stigmatellin is binding at Q_P, and the . the Int (Intermediate) position. It is called Int because it is intermediate between the other two positions. From the Int position the head can move toward cyto b where one of the His which is complexed with the Fe/S makes contact with the substrate binding at Q_P in cytochrome b. In the third position head the other His complexed with Fe/S becomes hydrogen bonded to a carboxylate oxygen of the heme in c1.

Q CycleQ Cycle

spinqualitylabelsall models PDB ID 1kyo Show:Asymmetric Unit Biological Assembly Drag the structure with the mouse to rotate   Export Animated Image

The cycle starts with the binding of UQH₂, ubiquinol, to cytochrome b at a Q_P site. In the applet to the right the Q_P site is binding stigmatellin. This binding causes the Rieske protein to flex at the hinge region rotating the Fe/S head so that the His which is bound to the Fe/S also binds to the UQH₂ at Q_P. Binding of the His to UQH₂ reduces its pK, and the quinol loses a proton. The position of Q_P in the complex is such that the proton which is lost diffuses to the intermembrane space.