Generation, characterization and crystallization of a cytochrome c(1)-subunit IV fused cytochrome bc(1) complex from Rhodobacter sphaeroides

The plethora of membrane respiratory chains in the phyla of life

The diversity of microbial cells is reflected in differences in cell size and shape, motility, mechanisms of cell division, pathogenicity or adaptation to different environmental niches. All these variations are achieved by the distinct metabolic strategies adopted by the organisms. The respiratory chains are integral parts of those strategies especially because they perform the most or, at least, most efficient energy conservation in the cell. Respiratory chains are composed of several membrane proteins, which perform a stepwise oxidation of metabolites toward the reduction of terminal electron acceptors. Many of these membrane proteins use the energy released from the oxidoreduction reaction they catalyze to translocate charges across the membrane and thus contribute to the establishment of the membrane potential, i.e. they conserve energy. In this work we illustrate and discuss the composition of the respiratory chains of different taxonomic clades, based on bioinformatic analyses and on biochemical data available in the literature. We explore the diversity of the respiratory chains of Animals, Plants, Fungi and Protists kingdoms as well as of Prokaryotes, including Bacteria and Archaea. The prokaryotic phyla studied in this work are Gammaproteobacteria, Betaproteobacteria, Epsilonproteobacteria, Deltaproteobacteria, Alphaproteobacteria, Firmicutes, Actinobacteria, Chlamydiae, Verrucomicrobia, Acidobacteria, Planctomycetes, Cyanobacteria, Bacteroidetes, Chloroflexi, Deinococcus-Thermus, Aquificae, Thermotogae, Deferribacteres, Nitrospirae, Euryarchaeota, Crenarchaeota and Thaumarchaeota.

Adrenergic receptor stimulation suppresses oxidative metabolism in isolated rat islets and Min6 cells

Insulin secretion is stimulated by glucose metabolism and inhibited by catecholamines through adrenergic receptor stimulation. We determined whether catecholamines suppress oxidative metabolism in β-cells through adrenergic receptors. In Min6 cells and isolated rat islets, epinephrine decreased oxygen consumption rates compared to vehicle control or co-administration of epinephrine with α2-adrenergic receptor antagonist yohimbine. Epinephrine also decreased forskolin-stimulated oxygen consumption rates, indicating cAMP dependent and independent actions. Furthermore, glucose oxidation rates were decreased with epinephrine, independent of the exocytosis of insulin, which was blocked with yohimbine. We evaluated metabolic targets through proteomic analysis after 4 h epinephrine exposure that revealed 466 differentially expressed proteins that were significantly enriched for processes including oxidative metabolism, protein turnover, exocytosis, and cell proliferation. These results demonstrate that acute α2-adrenergic stimulation suppresses glucose oxidation in β-cells independent of nutrient availability and insulin exocytosis, while cAMP concentrations are elevated. Proteomics and immunoblots revealed changes in electron transport chain proteins that were correlated with lower metabolic reducing equivalents, intracellular ATP concentrations, and altered mitochondrial membrane potential implicating a new role for adrenergic control of mitochondrial function and ultimately insulin secretion.

Universal Stress Protein Regulates Electron Transfer and Superoxide Generation Activities of the Cytochrome bc1 Complex from Rhodobacter sphaeroides

Interactions between Rhodobacter sphaeroides cytochrome bc1 complex (Rsbc1) and soluble cytosolic proteins were studied by a precipitation pull-down technique. After being purified, detergent-dispersed Rsbc1 complex was incubated with soluble cytosolic fraction and then dialyzed in the absence of detergent; the interacting proteins were coprecipitated with Rsbc1 complex upon centrifugation. One of the cytosolic proteins pulled down by Rsbc1 complex was identified by liquid chromatography-coupled tandem mass spectrometry (LC/MS/MS) to be the reported R. sphaeroides universal stress protein (UspA). Incubating purified UspA with the detergent dispersed bc1 complex resulted in an increase in the Rsbc1 complex activity by 60% and a decrease in superoxide generation activity by the complex by more than 70%. These UspA effects were only observed with Rsbc1 complexes containing subunit IV and assayed under aerobic conditions. These results suggest that the interaction between UspA and Rsbc1 complex may play an important role in R. sphaeroides cells during oxidative stress. Using a biotin label transfer technique, cytochrome c1 of the Rsbc1 complex was identified as the interacting site for UspA.

Oxygen dependent electron transfer in the cytochrome bc(1) complex

The effect of molecular oxygen on the electron transfer activity of the cytochrome bc(1) complex was investigated by determining the activity of the complex under the aerobic and anaerobic conditions. Molecular oxygen increases the activity of Rhodobacter sphaeroides bc(1) complex up to 82%, depending on the intactness of the complex. Since oxygen enhances the reduction rate of heme b(L), but shows no effect on the reduction rate of heme b(H), the effect of oxygen in the electron transfer sequence of the cytochrome bc(1) complex is at the step of heme b(L) reduction during bifurcated oxidation of ubiquinol.

Fusing proteins as an approach to study bioenergetic enzymes and processes

Fusing proteins is an attractive genetic tool used in several biochemical and biophysical investigations. Within a group of redox proteins, certain fusion constructs appear to provide valuable templates for spectroscopy with which specific bioenergetic questions can be addressed. Here we briefly summarize three different cases of fusions reported for bacterial cytochrome bc(1) (prokaryotic equivalent of mitochondrial respiratory complex III), a common component of electron transport chains. These fusions were used to study supramolecular organization of enzymatic complexes in bioenergetic membrane, influence of the accessory subunits on the activity and stability of the complex, and molecular mechanism of operation of the enzyme in the context of its dimeric structure. Besides direct connotation to molecular bioenergetics, these fusions also appeared interesting from the protein design, biogenesis, and assembly points of view. This article is part of a Special Issue entitled: 17th European Bioenergetics Conference (EBEC 2012).