title: Atypical features of Thermus thermophilus succinate:quinone reductase.
abstract: The Thermus thermophilus succinate:quinone reductase (SQR), serving as the respiratory complex II, has been homologously produced under the control of a constitutive promoter and subsequently purified. The detailed biochemical characterization of the resulting wild type (wt-rcII) and His-tagged (rcII-His(8)-SdhB and rcII-SdhB-His(6)) complex II variants showed the same properties as the native enzyme with respect to the subunit composition, redox cofactor content and sensitivity to the inhibitors malonate, oxaloacetate, 3-nitropropionic acid and nonyl-4-hydroxyquinoline-N-oxide (NQNO). The position of the His-tag determined whether the enzyme retained its native trimeric conformation or whether it was present in a monomeric form. Only the trimer exhibited positive cooperativity at high temperatures. The EPR signal of the [2Fe-2S] cluster was sensitive to the presence of substrate and showed an increased rhombicity in the presence of succinate in the native and in all recombinant forms of the enzyme. The detailed analysis of the shape of this signal as a function of pH, substrate concentration and in the presence of various inhibitors and quinones is presented, leading to a model for the molecular mechanism that underlies the influence of succinate on the rhombicity of the EPR signal of the proximal iron-sulfur cluster.
authors: Chemical and Environmental Sciences Department and Materials & Surface Science Institute, University of Limerick, Limerick, Ireland.
authors: Olga
authors: O
authors: Kolaj-Robin
authors: Mohamed R
authors: MR
authors: Noor
authors: Sarah R
authors: SR
authors: O'Kane
authors: Frauke
authors: F
authors: Baymann
authors: Tewfik
authors: T
authors: Soulimane
mesh_terms: D001426:Bacterial Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D004578:Electron Spin Resonance Spectroscopy; D042963:Electron Transport Complex II / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D006358:Hot Temperature; D006912:Hydroxyquinolines / Q000737:chemistry; D007700:Kinetics; D009574:Nitro Compounds / Q000737:chemistry; D062907:Oxaloacetic Acid / Q000737:chemistry; D010084:Oxidation-Reduction; D011401:Promoter Regions, Genetic; D011422:Propionates / Q000737:chemistry; D055503:Protein Multimerization; D011809:Quinones / Q000737:chemistry / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D013379:Substrate Specificity; D019802:Succinic Acid / Q000737:chemistry / Q000378:metabolism*; D016963:Thermus thermophilus / Q000737:chemistry / Q000201:enzymology*
chemical_list: D001426:Bacterial Proteins; D006912:Hydroxyquinolines; D009574:Nitro Compounds; D011422:Propionates; D011809:Quinones; D011993:Recombinant Fusion Proteins; D062907:Oxaloacetic Acid; C010494:nonyl-4-hydroxyquinoline-N-oxide; D019802:Succinic Acid; D042963:Electron Transport Complex II; C015392:3-nitropropionic acid