Nature 402, 377 - 385 (1999) © Macmillan Publishers Ltd.
C. ROY D. LANCASTER, ACHIM KRÖGER, MANFRED AUER & HARTMUT MICHEL
Abstract
Fumarate reductase couples the reduction of fumarate to succinate to the oxidation of quinol to quinone, in a reaction opposite to that catalysed by the related complex II of the respiratory chain (succinate dehydrogenase). Here we describe the crystal structure at 2.2 Å resolution of the three protein subunits containing fumarate reductase from the anaerobic bacterium Wolinella succinogenes. Subunit A contains the site of fumarate reduction and a covalently bound flavin adenine dinucleotide prosthetic group. Subunit B contains three iron-sulphur centres. The menaquinol-oxidizing subunit C consists of five membrane-spanning, primarily helical segments and binds two haem b molecules. On the basis of the structure, we propose a pathway of electron transfer from the dihaem cytochrome b to the site of fumarate reduction and a mechanism of fumarate reduction. The relative orientations of the soluble and membrane-embedded subunits of succinate:quinone oxidoreductases appear to be unique.
See notes on succinate:fumarate oxidoreductase for an introduction to Complex II of the respiratory chain. The fumarate reductase is a closely related enzyme that normally functions in the reverse direction, using menaquinol from the membrane to reduce fumarate to succinate. In the initial view, the dimeric complex is shown as a ribbon model colored by chain, with prosthetic groups as ball and stick models, except for iron sulfur clusters, shown as spacefilling atoms. The complex is shown vertical with respect to the membrane plane, with the P-phase (bacterial periplasm, mitochondrial inter-membrane space) at botton, N-phase (bacterial cytplasm, mitochondrial matrix) at top. One monomer (chains A, B, and C) is colored dark through pale blue, the second (chains D, E, and F) is colored green blue through green. The "extra" prosthetic group is a lauryl maltoside detergent molecule (not a quinone). (To stop or start rotation, click on image with right mouse button, and select Rotation.)
Reset view of the protein as a backbone model. Chain A, Chain B, Chain C. The protein is color-coded to show structure; helices are pink, coils white, sheets orange. The prosthetic groups are shown as spacefilling models colored by chain. The trans-membrane helices in the membrane spanning segments (chains C and F) are obvious in the lower half of the structure. Prosthetic groups in CPK. Also shown are crystallographic water molecules (represented by their O-atoms). Show liganding of FAD. The sites are in chains A and D of the two monomers. Only A is shown. The flavin and the covalenetly bonded histidine (His-43) are shown as a fatter tube models. Show the chain of iron sulfur centers connecting the substrate and menaquinone binding sites. Note that (in order from the FAD end) we have a [2Fe-2S] center, a [4Fe-4S] center, and a [3Fe-4S] center, the latter with only 3 liganding cysteines. From the distances between centers, it appears likely that all the clusters are in the electron transfer path, despite the wide range of Em values. ©Copyright 1996, Antony Crofts, University of Illinois at Urbana-Champaign, a-crofts@uiuc.edu
The protein is color-coded to show structure; helices are pink, coils white, sheets orange. The prosthetic groups are shown as spacefilling models colored by chain. The trans-membrane helices in the membrane spanning segments (chains C and F) are obvious in the lower half of the structure. Prosthetic groups in CPK. Also shown are crystallographic water molecules (represented by their O-atoms). Show liganding of FAD. The sites are in chains A and D of the two monomers. Only A is shown. The flavin and the covalenetly bonded histidine (His-43) are shown as a fatter tube models. Show the chain of iron sulfur centers connecting the substrate and menaquinone binding sites. Note that (in order from the FAD end) we have a [2Fe-2S] center, a [4Fe-4S] center, and a [3Fe-4S] center, the latter with only 3 liganding cysteines. From the distances between centers, it appears likely that all the clusters are in the electron transfer path, despite the wide range of Em values. ©Copyright 1996, Antony Crofts, University of Illinois at Urbana-Champaign, a-crofts@uiuc.edu
Prosthetic groups in CPK. Also shown are crystallographic water molecules (represented by their O-atoms). Show liganding of FAD. The sites are in chains A and D of the two monomers. Only A is shown. The flavin and the covalenetly bonded histidine (His-43) are shown as a fatter tube models. Show the chain of iron sulfur centers connecting the substrate and menaquinone binding sites. Note that (in order from the FAD end) we have a [2Fe-2S] center, a [4Fe-4S] center, and a [3Fe-4S] center, the latter with only 3 liganding cysteines. From the distances between centers, it appears likely that all the clusters are in the electron transfer path, despite the wide range of Em values. ©Copyright 1996, Antony Crofts, University of Illinois at Urbana-Champaign, a-crofts@uiuc.edu
Show liganding of FAD. The sites are in chains A and D of the two monomers. Only A is shown. The flavin and the covalenetly bonded histidine (His-43) are shown as a fatter tube models. Show the chain of iron sulfur centers connecting the substrate and menaquinone binding sites. Note that (in order from the FAD end) we have a [2Fe-2S] center, a [4Fe-4S] center, and a [3Fe-4S] center, the latter with only 3 liganding cysteines. From the distances between centers, it appears likely that all the clusters are in the electron transfer path, despite the wide range of Em values. ©Copyright 1996, Antony Crofts, University of Illinois at Urbana-Champaign, a-crofts@uiuc.edu
Show the chain of iron sulfur centers connecting the substrate and menaquinone binding sites. Note that (in order from the FAD end) we have a [2Fe-2S] center, a [4Fe-4S] center, and a [3Fe-4S] center, the latter with only 3 liganding cysteines. From the distances between centers, it appears likely that all the clusters are in the electron transfer path, despite the wide range of Em values. ©Copyright 1996, Antony Crofts, University of Illinois at Urbana-Champaign, a-crofts@uiuc.edu