title: Complex II from a structural perspective.
abstract: The super-macromolecular complex, succinate:quinone oxidoreductase (SQR, Complex II, succinate dehydrogenase) couples the oxidation of succinate in the matrix / cytoplasm to the reduction of quinone in the membrane. This function directly connects the Krebs cycle and the aerobic respiratory chain. Until the recent first report of the structure of SQR from Escherichia coli (E. coli) the structure-function relationships in SQR have been inferred from the structures of the homologous QFR, which catalyses the same reaction in the opposite direction. The structure of SQR from E. coli, analogous to the mitochondrial respiratory Complex II, has provided new insight into SQR's molecular design and mechanism, revealing the electron transport pathway through the enzyme. Comparison of the structures of SQR, QFR and other related flavoproteins shows how common amino acid residues at the interface of two domains facilitate the inter-conversion of succinate and fumarate. Additionally, the structure has provided a possible explanation as to why certain organisms utilise both SQR and QFR despite the fact that both can catalyse the inter-conversion of succinate and fumarate, in vitro and in vivo. Here we review how this structure has advanced our knowledge of this important enzyme and compare the structural information to other members of the Complex II superfamily and related flavoproteins.
authors.affiliation: Department of Biological Sciences, Imperial College London, SW7 2AZ, UK. b.byrne@imperial.ac.uk
authors.forename: Rob
authors.initials: R
authors.lastname: Horsefield
authors.forename: So
authors.initials: S
authors.lastname: Iwata
authors.forename: Bernadette
authors.initials: B
authors.lastname: Byrne
mesh_terms: D000594:Amino Acid Oxidoreductases / Q000737:chemistry / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001426:Bacterial Proteins / Q000737:chemistry / Q000378:metabolism; D002384:Catalysis; D020134:Catalytic Domain; D018360:Crystallography, X-Ray; D003574:Cytochrome c Group / Q000737:chemistry / Q000378:metabolism; D042963:Electron Transport Complex II / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000378:metabolism; D005420:Flavoproteins / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry / Q000378:metabolism; D008954:Models, Biological; D008958:Models, Molecular; D008969:Molecular Sequence Data; D015394:Molecular Structure; D010088:Oxidoreductases / Q000737:chemistry / Q000378:metabolism; D020836:Protein Structure, Quaternary; D021122:Protein Subunits / Q000737:chemistry / Q000378:metabolism; D017382:Reactive Oxygen Species / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013385:Succinate Dehydrogenase / Q000737:chemistry / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D003574:Cytochrome c Group; D029968:Escherichia coli Proteins; D005420:Flavoproteins; D008565:Membrane Proteins; D021122:Protein Subunits; D017382:Reactive Oxygen Species; C108096:SDHC protein, human; C084271:SdhA protein, Bacteria; D010088:Oxidoreductases; D042963:Electron Transport Complex II; C112400:flavocytochrome c3; C424907:quinol fumarate reductase; D013385:Succinate Dehydrogenase; D000594:Amino Acid Oxidoreductases; C031955:L-aspartate oxidase, E coli