Structure of a [2Fe–2S] ferredoxin from Rhodobacter capsulatus likely involved in Fe–S cluster biogenesis and conformational changes observed upon reduction

FdVI from Rhodobacter capsulatus is structurally related to a group of [2Fe–2S] ferredoxins involved in iron–sulfur cluster biosynthesis. Comparative genomics suggested that FdVI and orthologs found in α-Proteobacteria are involved in this process. Here, the crystal structure of FdVI has been determined for both the oxidized and the reduced protein. The [2Fe–2S] cluster lies 6 Å below the protein surface in a hydrophobic pocket without access to the solvent. This particular cluster environment might explain why the FdVI midpoint redox potential (?306 mV at pH 8.0) did not show temperature or ionic strength dependence. Besides the four cysteines that bind the cluster, FdVI features an extra cysteine which is located close to the S1 atom of the cluster and is oriented in a position such that its thiol group points towards the solvent. Upon reduction, the general fold of the polypeptide chain was almost unchanged. The [2Fe–2S] cluster underwent a conformational change from a planar to a distorted lozenge. In the vicinity of the cluster, the side chain of Met24 was rotated by 180°, bringing its S atom within hydrogen-bonding distance of the S2 atom of the cluster. The reduced molecule also featured a higher content of bound water molecules, and more extensive hydrogen-bonding networks compared with the oxidized molecule. The unique conformational changes observed in FdVI upon reduction are discussed in the light of structural studies performed on related ferredoxins.     

Effects of acute and chronic STZ-induced diabetes on clock gene expression and feeding in the gastrointestinal tract

This study aims to establish the antiproliferative effects of PK11195, a peripheral benzodiazepine receptor antagonist (PBR) in rat mammary tumor cells. Breast tumors were induced by administration of a carcinogen, dimethylbenz[a]anthracene to 50-day-old female rats maintained on a standard AIN-76A diet with casein as the protein source. The tumors were developed approximately after 120 days. The tumors were of grade I (20%), grade II (60%), and grade III (20%). The tumors were isolated and cultured in DMEM/F12 media with supplements. We characterized the properties of the isolated cells and study the effect of PK11195 on those cells. We were successful in growing breast tumor cells up to 30 passages for cellular characterization. These cells had high reactivity with Ki-67 and PCNA antibodies suggesting high proliferation rate. These cells were highly invasive as evident by matrigel invading ability. Furthermore, these cells acquired a positive response for CD-31 and VEGF antibodies suggesting angiogenic potential, and also possessed migrating ability/motility as evident by the wound healing properties. These cells expressed elevated levels of PBR, a cancer promoting gene. The proliferation, invasion and migration appear to decrease when treated with PK11195, a PBR antagonist. Furthermore, PK11195 treatment caused an increase in apoptosis as evident by increase in the levels of annexin V. However, the inhibition of cell proliferation by PK11195 was counteracted by Ro5-4864, a PBR agonist. Thus, PBR antagonist may be a potential therapeutic agent for the control of aggressiveness of breast cancer.     

Establishment of functional primary cultures of heart cells from the clam <Emphasis Type="Italic">Ruditapes decussatus</Emphasis>

Heart cells from the clam Ruditapes decussatus were routinely cultured with a high level of reproducibility in sea water based medium. Three cell types attached to the plastic after 2 days and could be maintained in vitro for at least 1 month: epithelial-like cells, round cells and fibroblastic cells. Fibroblastic cells were identified as functional cardiomyocytes due to their spontaneous beating, their ultrastructural characteristics and their reactivity with antibodies against sarcomeric α-actinin, sarcomeric tropomyosin, myosin and troponin T-C. Patch clamp measurements allowed the identification of ionic currents characteristic of cardiomyocytes: a delayed potassium current (I _K slow) strongly suppressed (95%) by tetraethylammonium (1 mM), a fast inactivating potassium current (I _K fast) inhibited (50%) by 4 amino-pyridine at 1 mM and, at a lower level (34%) by TEA, a calcium dependent potassium current (I _KCa) activated by strong depolarization. Three inward voltage activated currents were also characterized in some cardiomyocytes: L-type calcium current (I _Ca) inhibited by verapamil at 5 × 10⁻⁴ M, T-type Ca²⁺ current, rapidly activated and inactivated, and sodium current (I _Na) observed in only a few cells after strong hyperpolarization. These two currents did not seem to be physiologically essential in the initiation of the beatings of cardiomyocytes. Potassium currents were partially inhibited by tributyltin (TBT) (1 μM) but not by okadaic acid (two marine pollutants). DNA synthesis was also demonstrated in few cultured cells using BrdU (bromo-2′-deoxyuridine). Observed effects of okadaic acid and TBT demonstrated that cultured heart cells from clam Ruditapes decussatus can be used as an experimental model in marine toxicology.     

Mitochondrial DNA and inflammatory diseases

Increasing experimental evidence supports a connection between inflammation and mitochondrial dysfunction. Both acute and chronic inflammatory diseases course with elevated free radicals production that may affect mitochondrial proteins, lipids, and mtDNA. The subsequent mitochondrial impairment produces more reactive oxygen species that further reduce the ATP generation, increasing the probability of cell death. Mitochondrial impairment in now considered a key factor in inflammation because (1) there are specific pathologies directly derived from mtDNA mutations, causing chronic inflammatory diseases such as neuromuscular and neurodegenerative disorders, (2) there are neurodegenerative, metabolic, and other inflammatory diseases in which their progression is accompanied by mitochondrial dysfunction, which is directly involved in the cell death. Recently, a direct implication of mitochondrial reactive oxygen species and, particularly, mtDNA in the innate immune response has been reported. Thus, the mitochondria should be considered targets for new therapies related to the treatment of acute and chronic inflammatory diseases, including the auto-inflammatory ones.     

Inorganic-binding peptides as tools for surface quality control

This paper highlights an innovative application of inorganic-binding peptides as quality control tools for detecting defects on inorganic surfaces of any shape. The approach involves attaching a fluorescent label to an inorganic-binding peptide and exploiting the peptide's high binding specificity to detect, by simple fluorescence microscopy, chemical composition defects of µm size and crystallographic state defects. Proof of concept was demonstrated by monitoring binding of a previously isolated ZnO-binding peptide to galvanized steel substrates. The approach was further validated for TiO₂ coatings and stainless steel, with two new, specific inorganic-binding peptides isolated by phage display.     

A Model-Based Approach to Detection Limits in Studying Environmental Exposures and Human Fecundity

Statistics in Biosciences - Human exposure to persistent environmental pollutants often results in concentrations with a range of values below the laboratory detection limits. Growing evidence...     

Development of an in vitro culture method for cells and tissues from the zebra mussel (<Emphasis Type="Italic">Dreissena polymorpha</Emphasis>)

Despite the successful transfer of mammalian in vitro techniques for use with fish and other vertebrates, little progress has been made in the area of invertebrate tissue culture. This paper describes the development of an in vitro technique for the culture of both cells in suspension and tissue explants from the gill, digestive gland and mantle of the zebra mussel (Dreissena polymorpha) and their successful maintenance in culture for up to 14 days. Cell suspensions from the gills and digestive gland were the most successful technique developed with viability >80% maintained for up to 8 days in culture, suitable for use in short term toxicity tests. Tissue explants from the mantle were also maintained in culture for up to 14 days. This paper describes the challenges involved in the development of a novel in vitro culture technique for aquatic invertebrates.