Background: Xylans are polysaccharides that are naturally abundant in agricultural by-products, such as cereal brans and straws. Microbial degradation of arabinoxylan is facilitated by extracellular esterases that remove acetyl, feruloyl, and p-coumaroyl decorations. The bacterium Ruminiclostridium cellulolyticum possesses the Xua (xylan utilization associated) system, which is responsible for importing and intracellularly degrading arabinoxylodextrins.
View Article and Find Full Text PDFA family of bacterial copper storage proteins (the Csps) possess thiolate-lined four-helix bundles whose cores can be filled with Cu(I) ions. The majority of Csps are cytosolic (Csp3s), and in vitro studies carried out to date indicate that the Csp3s from OB3b (Csp3), (Csp3), and (Csp3) are alike. Bioinformatics have highlighted homologues with potentially different Cu(I)-binding properties from these characterized "classical" Csp3s.
View Article and Find Full Text PDFXyloglucan utilization by was formerly shown to imply the uptake of large xylogluco-oligosaccharides, followed by cytosolic depolymerization into glucose, galactose, xylose, and cellobiose. This raises the question of how the anaerobic bacterium manages the simultaneous presence of multiple sugars. Using genetic and biochemical approaches targeting the corresponding metabolic pathways, we observed that, surprisingly, all sugars are catabolized, collectively, but glucose consumption is prioritized.
View Article and Find Full Text PDFThe necessity to decrease our fossil energy dependence requests bioprocesses based on biomass degradation. Cellobiose is the main product released by cellulases when acting on the major plant cell wall polysaccharide constituent, the cellulose. , one of the most common model organisms for the academy and the industry, is unable to metabolize this disaccharide.
View Article and Find Full Text PDFCellulosomes are large plant cell wall degrading complexes secreted by some anaerobic bacteria. They are typically composed of a major scaffolding protein containing multiple receptors called cohesins, which tightly anchor a small complementary module termed dockerin harbored by the cellulosomal enzymes. In the present study, we have successfully cell surface exposed in Escherichia coli a hybrid scaffoldin, Scaf6, fused to the curli protein CsgA, the latter is known to polymerize at the surface of E.
View Article and Find Full Text PDFCellulosomes are complex nanomachines produced by cellulolytic anaerobic bacteria such as Ruminiclostridium cellulolyticum (formerly known as Clostridium cellulolyticum). Cellulosomes are composed of a scaffoldin protein displaying several cohesin modules on which enzymatic components can bind to through their dockerin module. Although cellulosomes have been studied for decades, very little is known about the dynamics of complex assembly.
View Article and Find Full Text PDFBackground: In anaerobic cellulolytic micro-organisms, cellulolysis results in the action of several cellulases gathered in extracellular multi-enzyme complexes called cellulosomes. Their action releases cellobiose and longer cellodextrins which are imported and further degraded in the cytosol to fuel the cells. In , an anaerobic and cellulolytic mesophilic bacteria, three cellodextrin phosphorylases named CdpA, CdpB, and CdpC, were identified in addition to the cellobiose phosphorylase (CbpA) previously characterized.
View Article and Find Full Text PDFRuminiclostridium cellulolyticum and Lachnoclostridium phytofermentans are cellulolytic clostridia either producing extracellular multienzymatic complexes termed cellulosomes or secreting free cellulases respectively. In the free state, the cellulase Cel9A secreted by L. phytofermentans is much more active on crystalline cellulose than any cellulosomal family-9 enzyme produced by R.
View Article and Find Full Text PDFRuminiclostridium cellulolyticum produces extracellular cellulosomes which contain interalia numerous family-9 glycoside hydrolases, including the inactive Cel9V. The latter shares the same organization and 79% sequence identity with the active cellulase Cel9E. Nevertheless, two aromatic residues and a four-residue stretch putatively critical for the activity are missing in Cel9V.
View Article and Find Full Text PDFBacteria are thought to avoid using the essential metal ion copper in their cytosol due to its toxicity. Herein we characterize Csp3, the cytosolic member of a new family of bacterial copper storage proteins from Methylosinus trichosporium OB3b and Bacillus subtilis. These tetrameric proteins possess a large number of Cys residues that point into the cores of their four-helix bundle monomers.
View Article and Find Full Text PDFMethane-oxidizing bacteria (methanotrophs) require large quantities of copper for the membrane-bound (particulate) methane monooxygenase. Certain methanotrophs are also able to switch to using the iron-containing soluble methane monooxygenase to catalyse methane oxidation, with this switchover regulated by copper. Methane monooxygenases are nature's primary biological mechanism for suppressing atmospheric levels of methane, a potent greenhouse gas.
View Article and Find Full Text PDFThe ability to respire sulfate linked to lactate oxidation is a key metabolic signature of the Desulfovibrio genus. Lactate oxidation by these incomplete oxidizers generates reductants through lactate dehydrogenase (LDH) and pyruvate-ferredoxin oxidoreductase (PFOR), with the latter catalyzing pyruvate conversion into acetyl-CoA. Acetyl-CoA is the source of substrate-level phosphorylation through the production of ATP.
View Article and Find Full Text PDFNew information on a protein's structure, intra- and intermolecular hydrogen bonds, or metal-ligand bond properties can be unraveled in the far-infrared (far-IR)-terahertz-domain (600-3 cm(-1) or 18-0.1 THz). In this study, we compare the performances of thermal sources with synchrotron far-IR to record reaction-induced Fourier transform infrared (FT-IR) difference signals with proteins in solution.
View Article and Find Full Text PDFCytoplasmic desulfothioredoxin (Dtrx) from the anaerobe Desulfovibrio vulgaris Hildenborough has been identified as a new member of the thiol disulfide oxidoreductase family. The active site of Dtrx contains a particular consensus sequence, CPHC, never seen in the cytoplasmic thioredoxins and generally found in periplasmic oxidases. Unlike canonical thioredoxins (Trx), Dtrx does not present any disulfide reductase activity, but it presents instead an unusual disulfide isomerase activity.
View Article and Find Full Text PDFAngew Chem Int Ed Engl
August 2011
Vibrations of the metal active site of the Cu,Zn-superoxide dismutase enzyme were analyzed by far-infrared difference spectroscopy and theoretical normal mode calculation. Both electrochemically triggered Cu(I) and Cu(II) redox states show well-defined infrared vibrational modes, notably modes of the histidine ligands, the Cu(II)-His(61)-Zn(II) bridge and of the water pseudo-ligand.
View Article and Find Full Text PDFSulfate reducers have developed a multifaceted adaptative strategy to survive against oxidative stresses. Along with this oxidative stress response, we recently characterized an elegant reversible disulfide bond-dependent protective mechanism in the pyruvate:ferredoxin oxidoreductase (PFOR) of various Desulfovibrio species. Here, we searched for thiol redox systems involved in this mechanism.
View Article and Find Full Text PDFOxidative decarboxylation of pyruvate forming acetyl-coenzyme A is a crucial step in many metabolic pathways. In most anaerobes, this reaction is carried out by pyruvate-ferredoxin oxidoreductase (PFOR), an enzyme normally oxygen sensitive except in Desulfovibrio africanus (Da), where it shows an abnormally high oxygen stability. Using site-directed mutagenesis, we have specified a disulfide bond-dependent protective mechanism against oxidative conditions in Da PFOR.
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