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PubMed2006

Pathways of neurodegeneration and experimental models of basal ganglia disorders: downstream effects of mitochondrial inhibition.

The basal ganglia circuit plays a key role in the regulation of voluntary movements as well as in behavioural control and cognitive functions. The main pathogenic role of mitochondrial dysfunctions is now accepted in the neurodegenerative process and the mitochondria have been successfully used as subcellular targets to obtain relevant experimental models of basal ganglia neurodegenerative disorders. Mitochondrial toxins act through an inhibition of the respiratory chain complexes. These toxins, by uncoupling cellular respiration, shift the cell into a state of oxidative stress and trigger several bidirectional links with the excitotoxic process. Moreover, the in vitro inhibition of the respiratory chain complexes alters the electrophysiological properties of the neurons. The downstream effects triggered by mitochondrial complexes inhibition provide a model integrating genetic and environmental pathogenic factors to explain the selective neuronal vulnerability.

Animals↗
PubMed2005

Increased IRP1 activity in Friedreich ataxia.

In low-iron conditions, the cytosolic iron-regulatory protein IRP1 binds to iron-responsive elements (IREs) in mRNAs encoding iron-regulated proteins. In high-iron conditions, IRP1 incorporates an iron-sulfur cluster (ISC), which interferes with IRE binding and prevents intracellular iron accumulation. Here we demonstrate an incomplete shift of IRP1 to its ISC form in Friedreich ataxia (FRDA) fibroblasts, associated with decreased activities of ISC respiratory complexes. Our data suggest an impaired adaptive response to iron accumulation in FRDA cells.

Cells, Cultured↗
PubMed2006

Preservation of RNA and destruction of infectivity in microdissected brain tissues of Lewis rats infected with the Borna disease virus.

Laser microdissection combined with real-time RT-PCR presents an advanced tool to quantify particular RNA species in defined tissue areas. Dealing with infectious tissue samples increases the need to overcome the risk of infectivity and contamination during laser microdissection. Here, an useful method to control infectivity of frozen brain sections infected with the Borna disease virus (BDV), an enveloped RNA virus, is described. Various pre-treatments were applied prior to laser microdissection and subsequent real-time RT-PCR. Brain sections were incubated with Vennotrade mark Vet 1 super 1% or 70% ethanol for 30, 60 and 90min, followed by quantification of infectious virus and RNA recovery using laser microdissection. Total RNA specific for the BDV nucleoprotein (BDV-N) and the cellular genes glyceraldehyde-3-phosphate dehydrogenase (GAPDH), succinate-ubiquinone reductase (SDHA) and hypoxanthine phosphoribosyl-transferase-1 (HPRT) was measured by real-time RT-PCR and compared to BDV-infected control samples. After 30 min incubation with both disinfectants, no infectious virus was isolated, while sufficient cDNA copy numbers were amplified. As tissue morphology was best preserved after ethanol treatment, 30min incubation with 70% ethanol was selected as the method of choice to prevent infectivity of BDV. This procedure represents a suitable pre-treatment option to ensure adequate safety of virus infected central nervous system tissue.

Animals↗
PubMed2002

The Saccharomyces cerevisiae mitochondrial succinate:ubiquinone oxidoreductase.

The Saccharomyces cerevisiae succinate dehydrogenase (SDH) provides an excellent model system for studying the assembly, structure, and function of a mitochondrial succinate:quinone oxidoreductase. The powerful combination of genetic and biochemical approaches is better developed in yeast than in other eukaryotes. The yeast protein is strikingly similar to other family members in the structural and catalytic properties of its subunits. However, the membrane domain and particularly the role of the single heme in combination with two ubiquinone-binding sites need further investigation. The assembly of subunits and cofactors that occurs to produce new holoenzyme molecules is a complex process that relies on molecular chaperones. The yeast SDH provides the best opportunity for understanding the biogenesis of this family of iron-sulfur flavoproteins.

Amino Acid Sequence↗
PubMed2002

Succinate:quinone oxidoreductases from epsilon-proteobacteria.

The epsilon-proteobacteria form a subdivision of the Proteobacteria including the genera Wolinella, Campylobacter, Helicobacter, Sulfurospirillum, Arcobacter and Dehalospirillum. The majority of these bacteria are oxidase-positive microaerophiles indicating an electron transport chain with molecular oxygen as terminal electron acceptor. However, numerous members of the epsilon-proteobacteria also grow in the absence of oxygen. The common presence of menaquinone and fumarate reduction activity suggests anaerobic fumarate respiration which was demonstrated for the rumen bacterium Wolinella succinogenes as well as for Sulfurospirillum deleyianum, Campylobacter fetus, Campylobacter rectus and Dehalospirillum multivorans. To date, complete genome sequences of Helicobacter pylori and Campylobacter jejuni are available. These bacteria and W. succinogenes contain the genes frdC, A and B encoding highly similar heterotrimeric enzyme complexes belonging to the family of succinate:quinone oxidoreductases. The crystal structure of the W. succinogenes quinol:fumarate reductase complex (FrdCAB) was solved recently, thus providing a model of succinate:quinone oxidoreductases from epsilon-proteobacteria. Succinate:quinone oxidoreductases are being discussed as possible therapeutic targets in the treatment of several pathogenic epsilon-proteobacteria.

Citric Acid Cycle↗
PubMed2002

Succinate:quinone oxidoreductase in the bacteria Paracoccus denitrificans and Bacillus subtilis.

An overview of the present knowledge about succinate:quinone oxidoreductase in Paracoccus denitrificans and Bacillus subtilis is presented. P. denitrificans contains a monoheme succinate:ubiquinone oxidoreductase that is similar to that of mammalian mitochondria with respect to composition and sensitivity to carboxin. Results obtained with carboxin-resistant P. denitrificans mutants provide information about quinone-binding sites on the enzyme and the molecular basis for the resistance. B. subtilis contains a diheme succinate:menaquinone oxidoreductase whose activity is dependent on the electrochemical gradient across the cytoplasmic membrane. Data from studies of mutant variants of the B. subtilis enzyme combined with available crystal structures of a similar enzyme, Wolinella succinogenes fumarate reductase, substantiate a proposed explanation for the mechanism of coupling between quinone reductase activity and transmembrane potential.

Amino Acid Sequence↗
PubMed2002

Purification, crystallisation and preliminary crystallographic studies of succinate:ubiquinone oxidoreductase from Escherichia coli.

A membrane protein complex, succinate dehydrogenase (SQR) from Escherichia coli has been purified and crystallised. This enzyme is composed of four subunits containing FAD, three iron-sulphur clusters and one haem b as prosthetic groups. The obtained crystals belong to the hexagonal space group P6(3) with the unit-cell dimensions of a=b=123.8 A and c=214.6 A. An asymmetric unit of the crystals contains one SQR monomer (M(r) 120 kDa). A data set is now available at 4.0 A resolution with 88.1% completeness and 0.106 R(merge). We have obtained a molecular replacement solution that shows sensible molecular packing, using the soluble domain of E. coli QFR (fumarate reductase) as a search model. The packing suggests that E. coli SQR is a crystallographic trimer rather than a dimer as observed for the E. coli QFR.

Crystallography↗
PubMed2002

Succinate dehydrogenase and fumarate reductase from Escherichia coli.

Succinate-ubiquinone oxidoreductase (SQR) as part of the trichloroacetic acid cycle and menaquinol-fumarate oxidoreductase (QFR) used for anaerobic respiration by Escherichia coli are structurally and functionally related membrane-bound enzyme complexes. Each enzyme complex is composed of four distinct subunits. The recent solution of the X-ray structure of QFR has provided new insights into the function of these enzymes. Both enzyme complexes contain a catalytic domain composed of a subunit with a covalently bound flavin cofactor, the dicarboxylate binding site, and an iron-sulfur subunit which contains three distinct iron-sulfur clusters. The catalytic domain is bound to the cytoplasmic membrane by two hydrophobic membrane anchor subunits that also form the site(s) for interaction with quinones. The membrane domain of E. coli SQR is also the site where the heme b556 is located. The structure and function of SQR and QFR are briefly summarized in this communication and the similarities and differences in the membrane domain of the two enzymes are discussed.

Binding Sites↗
PubMed2002

Quinol:fumarate oxidoreductases and succinate:quinone oxidoreductases: phylogenetic relationships, metal centres and membrane attachment.

A comprehensive phylogenetic analysis of the core subunits of succinate:quinone oxidoreductases and quinol:fumarate oxidoreductases is performed, showing that the classification of the enzymes as type A to E based on the type of the membrane anchor fully correlates with the specific characteristics of the two core subunits. A special emphasis is given to the type E enzymes, which have an atypical association to the membrane, possibly involving anchor subunits with amphipathic helices. Furthermore, the redox properties of the SQR/QFR proteins are also reviewed, stressing out the recent observation of redox-Bohr effect upon haem reduction, observed for the Desulfovibrio gigas and Rhodothermus marinus enzymes, which indicates a direct protonation event at the haems or at a nearby residue. Finally, the possible contribution of these enzymes to the formation/dissipation of a transmembrane proton gradient is discussed, considering recent experimental and structural data.

Amino Acid Sequence↗
PubMed1991

Inhibition of succinate-ubiquinone reductase by nitrosalicyl-N-alkylamides.

The abilities of eight nitrosalicyl-N-alkylamides to inhibit succinate-ubiquinone reductase were compared. These compounds possess both a nitro group at 3- or 5-position of the benzyl ring, and a methyl, decyl, dodecyl or tetradecyl group subsituted for the amide hydrogen of salicylamide. The result shows the following: (a) 3-Nitrosalicyl-N-alkylamides are stronger inhibitors than 5-nitrosalicyl-N-alkylamides when they have the same alkyl group. (b) The inhibitory abilities of both 3-and 5-nitrosalicyl-N-alkylamides increase with increasing alkyl group length. (c) Kinetic data show that the inhibition by 3-nitrosalicyl-N-tetradecylamide is noncompetitive with respect to the electron acceptor Q2.

Animals↗
PubMed1991

Involvement of a histidine residue in the interaction between membrane-anchoring protein (QPs) and succinate dehydrogenase in mitochondrial succinate-ubiquinone reductase.

The involvement of a histidine residue of the membrane-anchoring protein (QPs) fraction in reconstitution of succinate dehydrogenase to form succinate-ubiquinone reductase is studied by using a histidine-modifying reagent, diethylpyrocarbonate (DEPC). A maximum inactivation of 80% of reconstitutive activity is obtained when QPs is treated with 1 mM DEPC at 0 degrees C for 30 min in 50 mM Tris-HCl (pH 7.0). DEPC also inactivates about 85% of intact succinate-ubiquinone reductase. The inactivation of succinate-ubiquinone reductase by DEPC is a result of the modification of essential histidine residues of succinate dehydrogenase. The inactivation is not a result of the modification of the histidine residue in QPs which is essential for interaction with succinate dehydrogenase because the QPs dissociated from the inactivated succinate-ubiquinone reductase is active in reconstitution with active succinate-dehydrogenase. Apparently, the essential histidine in QPs is shielded by succinate dehydrogenase and thus inaccessible to DEPC modification in succinate-ubiquinone reductase. The involvement of a histidine residue of QPs in interaction with succinate dehydrogenase is further evident by the presence of 553 nm shoulder on the alpha-absorption peak of reduced cytochrome b-560 (a characteristic of physical association of QPs with succinate dehydrogenase) in the DEPC-inactivated succinate-ubiquinone reductase. This shoulder disappears from a mixture of succinate dehydrogenase and DEPC-treated QPs when reduced with dithionite. About one histidine residue per molecule of QPs is modified in the DEPC-treated sample, suggesting that only one histidine residue is essential for interaction with succinate dehydrogenase. This essential histidine group is located in the smaller subunit (Mr 13,000) of QPs.

Diethyl Pyrocarbonate↗
PubMed1998

Reconstitution of cytochrome b-560 (QPs1) of bovine heart mitochondrial succinate-ubiquinone reductase.

The QPs1 subunit of bovine heart mitochondrial succinate-ubiquinone reductase was overexpressed in Escherichia coli DH5 alpha cells as a glutathione S-transferase fusion protein (GST-QPs1) using the expression vector, pGEX/QPs1. The yield of soluble active recombinant GST-QPs1 fusion protein depends on the IPTG concentration, induction growth time, temperature, and medium. Maximum yield of recombinant fusion protein was obtained from cells harvested 3 h postinduction of growth with 0.5 mM IPTG at 27 degrees C in an enriched medium containing betaine and sorbitol. QPs1 is released from the fusion protein by proteolytic cleavage with thrombin. Isolated recombinant QPs1 shows one protein band in SDS-polyacrylamide gel electrophoresis corresponding to subunit III of mitochondrial succinate-ubiquinone reductase. However, partial N-terminal amino acid sequence analysis of recombinant QPs1 shows two extra amino acid residues, glycine and serine, at the N-terminus of mature QPs1, resulting from the recombinant manipulation. When isolated recombinant QPs1 is dispersed in 0.01% dodecyl maltoside, it is in a highly aggregated form with an apparent molecular mass of over 1 million. Recombinant GST-QPs1 contains little cytochrome b-560 heme. However, addition of hemin chloride restores the spectral characteristics of cytochrome b-560. Cytochrome b-560 restoration varies with the amount of hemin used. Maximum reconstitution is obtained when the molar ratio of heme to fusion protein used in the system is 0.6. Reconstituted cytochrome b-560 shows a EPR signal at g = 2.91 which corresponds to one of the EPR signals of cytochrome b-560 in a QPs preparation. When GST-QPs1 with reconstituted cytochrome b-560 is treated with thrombin to cleave GST from QPs1, no change in the absorption and EPR characteristics of cytochrome b-560 is observed, indicating that the bis-histidine ligands of reconstituted cytochrome b-560 are provided by QPs1.

Amino Acid Sequence↗