Succinate Dehydrogenase: Difference between revisions
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===Structure | ===Structure=== | ||
The tetramer is composed of two hydrophilic and two hydrophobic subunits. The hydrophilic subunits are named SdhA and SdhB; the former is a flavoprotein containing a covalently-bound FAD cofactor a binding site for succinate, while the latter is Fe-S protein bearing the three iron-sulfur clusters 2Fe-2S, 3Fe-4S, and 4Fe-4S. The hydrophobic subunits, termed SdhC and SdhD, anchor the protein in the mitochondrial membrane and formally comprise cytochrome b <ref>PMID:12966066</ref> and <ref>PMID:12560550</ref>. This cytochrome contains six transmembrane α-helices, a heme b group, and a binding site for ubiquinone located in a space bounded by SdhB, SdhC, and SdhD <ref>PMID:12560550</ref> and <ref>PMID:16407191</ref>. | The tetramer is composed of two hydrophilic and two hydrophobic subunits. The hydrophilic subunits are named SdhA and SdhB; the former is a flavoprotein containing a covalently-bound FAD cofactor a binding site for succinate, while the latter is Fe-S protein bearing the three iron-sulfur clusters 2Fe-2S, 3Fe-4S, and 4Fe-4S. The hydrophobic subunits, termed SdhC and SdhD, anchor the protein in the mitochondrial membrane and formally comprise cytochrome b <ref>PMID:12966066</ref> and <ref>PMID:12560550</ref>. This cytochrome contains six transmembrane α-helices, a heme b group, and a binding site for ubiquinone located in a space bounded by SdhB, SdhC, and SdhD <ref>PMID:12560550</ref> and <ref>PMID:16407191</ref>. | ||
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{{STRUCTURE_1nek | PDB=1nek | SCENE= }} | {{STRUCTURE_1nek | PDB=1nek | SCENE= }} | ||
===Binding sites | ===Binding sites=== | ||
====Succinate==== | ====Succinate==== | ||
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===Mechanisms | ===Mechanisms=== | ||
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====Ubiquinone reduction==== | ====Ubiquinone reduction==== | ||
Ubiquinone is initially oriented in the active site such that the O1 carbonyl group interacts with Tyr83 of SdhD via hydrogen bonding. The electrons removed during the oxidation reaction are conveyed through the iron-sulfur clusters to 3Fe-4S; their presence on that cluster stimulates the substrate to reorient so that a second hydrogen bond between the O4 carbonyl group and Ser27 of SdhC may form. The electrons are transferred to the substrate individually, with the addition of the first producing a radical semiquinone and the second completing the reduction to ubiquinol. This mechanism is illustrated in image 3 <ref>PMID:16950775</ref>. | Ubiquinone is initially oriented in the active site such that the O1 carbonyl group interacts with Tyr83 of SdhD via hydrogen bonding. The electrons removed during the oxidation reaction are conveyed through the iron-sulfur clusters to 3Fe-4S; <scene name='Michael_Vick_Sandbox_2/Ubq_binding_site/1'>their presence on that cluster stimulates the substrate to reorient so that a second hydrogen bond between the O4 carbonyl group and Ser27 of SdhC may form.</scene> The electrons are transferred to the substrate individually, with the addition of the first producing a radical semiquinone and the second completing the reduction to ubiquinol. This mechanism is illustrated in image 3 <ref>PMID:16950775</ref>. | ||
[[Image:QuinoneMechanism.gif]] | [[Image:QuinoneMechanism.gif]] | ||