Project description:The 22 kDa SoxYZ protein complex from the green sulfur bacterium Chlorobium limicola f. thiosulfatophilum is a central player in the sulfur-oxidizing (Sox) enzyme system of the organism by activating thiosulfate for oxidation by SoxXA and SoxB. It has been proposed that SoxYZ exists as a heterodimer or heterotetramer, but the properties and role of the individual components of the complex thus far remain unknown. Here, the heterologous expression, purification, and the crystallization of stable tetrameric SoxY are reported. Crystals of SoxY diffract to 2.15 A resolution and belong to space group C222(1), with unit-cell parameters a = 41.22, b = 120.11, c = 95.30 A. MIRAS data from Pt(2+)- and Hg(2+)-derivatized SoxY crystals resulted in an interpretable electron-density map at 3 A resolution after density modification.
Project description:Desulfurella amilsii is an acidotolerant sulfur-reducing bacterium isolated from sediments of an acidic river. It can grow in a broad range of pH and can obtain energy via respiring elemental sulfur or thiosulfate, as well as by disproportionating elemental sulfur. Its genome encodes the enzyme sulfur reductase, and several rhodanese-like proteins, possibly playing a role in sulfur respiration and disproportionation. Thiosulfate reductase and dissimilatory sulfite reductase are encoded and might play a role during the respiration of thiosulfate. The involvement of these enzymes in the reductive routes of sulfur metabolism is not yet clearly understood. Desulfurella amilsii was used in this study to combine strategies for sulfur metabolism research on the protein level to shed some light on the pathways involved in the metabolism of this microorganism.
Project description:We have determined the atomic structure of the bacteriochlorophyll c (BChl c) assembly in a huge light-harvesting organelle, the chlorosome of green photosynthetic bacteria, by solid-state NMR. Previous electron microscopic and spectroscopic studies indicated that chlorosomes have a cylindrical architecture with a diameter of approximately 10 nm consisting of layered BChl molecules. Assembly structures in huge noncrystalline chlorosomes have been proposed based mainly on structure-dependent chemical shifts and a few distances acquired by solid-state NMR, but those studies did not provide a definite structure. Our approach is based on (13)C dipolar spin-diffusion solid-state NMR of uniformly (13)C-labeled chlorosomes under magic-angle spinning. Approximately 90 intermolecular C C distances were obtained by simultaneous assignment of distance correlations and structure optimization preceded by polarization-transfer matrix analysis. It was determined from the approximately 90 intermolecular distances that BChl c molecules form piggyback-dimer-based parallel layers. This finding rules out the well known monomer-based structures. A molecular model of the cylinder in the chlorosome was built by using this structure. It provided insights into the mechanisms of efficient light harvesting and excitation transfer to the reaction centers. This work constitutes an important advance in the structure determination of huge intact systems that cannot be crystallized.
Project description:Dissimilatory oxidation of thiosulfate in the green sulfur bacterium Chlorobium limicola f. thiosulfatophilum is carried out by the ubiquitous sulfur-oxidizing (Sox) multi-enzyme system. In this system, SoxY plays a key role, functioning as the sulfur substrate-binding protein that offers its sulfur substrate, which is covalently bound to a conserved C-terminal cysteine, to another oxidizing Sox enzyme. Here, we report the crystal structures of a stand-alone SoxY protein of C. limicola f. thiosulfatophilum, solved at 2.15 A and 2.40 A resolution using X-ray diffraction data collected at 100 K and room temperature, respectively. The structure reveals a monomeric Ig-like protein, with an N-terminal alpha-helix, that oligomerizes into a tetramer via conserved contact regions between the monomers. The tetramer can be described as a dimer of dimers that exhibits one large hydrophobic contact region in each dimer and two small hydrophilic interface patches in the tetramer. At the tetramer interface patch, two conserved redox-active C-terminal cysteines form an intersubunit disulfide bridge. Intriguingly, SoxY exhibits a dimer/tetramer equilibrium that is dependent on the redox state of the cysteines and on the type of sulfur substrate component bound to them. Taken together, the dimer/tetramer equilibrium, the specific interactions between the subunits in the tetramer, and the significant conservation level of the interfaces strongly indicate that these SoxY oligomers are biologically relevant.
Project description:Aquifex aeolicus is a microaerophilic hydrogen- and sulfur -oxidizing bacterium that assimilates CO2 via the reverse tricarboxylic acid cycle (rTCA). Key enzymes of this pathway are pyruvate:ferredoxin oxidoreductase (PFOR) and 2-oxoglutarate:ferredoxin oxidoreductase (OGOR), which are responsible, respectively, for the reductive carboxylation of acetyl-CoA to pyruvate and of succinyl-CoA to 2-oxoglutarate, two energetically unfavorable reactions that require a strong reduction potential. We have confirmed, by biochemistry and proteomics, that A. aeolicus possesses a pentameric version of these enzyme complexes ((αβγδε)2) and that they are highly abundant in the cell. In addition, we have purified and characterized from the soluble fraction of A. aeolicus, two low redox potential and oxygen-stable [4Fe-4S] ferredoxins (Fd6 and Fd7, E0 = -440 and -460 mV respectively) and have shown that they can physically interact and exchange electrons with both PFOR and OGOR, suggesting that they could be the physiological electron donors of the system in vivo. Shotgun proteomics indicated that all the enzymes assumed to be involved in the rTCA cycle are produced in the A. aeolicus cells. A number of additional enzymes, previously suggested to be part of a putative partial Wood-Ljungdahl pathway used for the synthesis of serine and glycine from CO2 [1], were identified by mass spectrometry, but their abundance in the cell seem to be much lower than those of the rTCA cycle. Their possible involvement in the carbon assimilation is discussed. 1- Braakman, R.; Smith, E. Metabolic Evolution of a Deep-Branching Hyperthermophilic Chemoautotrophic Bacterium. PloS One 2014, 9, e87950, doi:10.1371/journal.pone.0087950.