Redox transfer at subduction zones: insights from Fe isotopes in the Mariana forearc

Subduction zones are active sites of chemical exchange between the Earth’s surface and deep interior and play a fundamental role in regulating planet habitability. However, the mechanisms by which redox sensitive elements (e.g., iron, carbon and sulfur) are cycled during subduction remains unclear. Here we use Fe stable isotopes (δ56Fe), which are sensitive to redox-related processes, to examine forearc serpentinite clasts recovered from deep sea drilling of mud volcanoes formed above the Mariana subduction zone in the Western Pacific. We show that serpentinisation of the forearc by slab-derived fluids produces dramatic δ56Fe variation. Unexpected negative correlations between serpentinite bulk δ56Fe, fluid-mobile element concentrations (e.g., B, As) and Fe3+/ƩFe suggest a concomitant oxidation of the mantle wedge through the transfer of isotopically light iron by slab-derived fluids. This process must reflect the transfer of either sulfate- or carbonate-bearing fluids that preferentially complex isotopically light Fe

Engineering of Three-Finger Fold Toxins Creates Ligands with Original Pharmacological Profiles for Muscarinic and Adrenergic Receptors

Protein engineering approaches are often a combination of rational design and directed evolution using display technologies. Here, we test “loop grafting,” a rational design method, on three-finger fold proteins. These small reticulated proteins have exceptional affinity and specificity for their diverse molecular targets, display protease-resistance, and are highly stable and poorly immunogenic. The wealth of structural knowledge makes them good candidates for protein engineering of new functionality. Our goal is to enhance the efficacy of these mini-proteins by modifying their pharmacological properties in order to extend their use in imaging, diagnostics and therapeutic applications. Using the interaction of three-finger fold toxins with muscarinic and adrenergic receptors as a model, chimeric toxins have been engineered by substituting loops on toxin MT7 by those from toxin MT1. The pharmacological impact of these grafts was examined using binding experiments on muscarinic receptors M1 and M4 and on the α1A-adrenoceptor. Some of the designed chimeric proteins have impressive gain of function on certain receptor subtypes achieving an original selectivity profile with high affinity for muscarinic receptor M1 and α1A-adrenoceptor. Structure-function analysis supported by crystallographic data for MT1 and two chimeras permits a molecular based interpretation of these gains and details the merits of this protein engineering technique. The results obtained shed light on how loop permutation can be used to design new three-finger proteins with original pharmacological profiles

First assessment of the comparative toxicity of ivermectin and moxidectin in adult dung beetles: Sub-lethal symptoms and pre-lethal consequences

Among macrocyclic lactones (ML), ivermectin (IVM) and moxidectin (MOX) potentially affect all Ecdysozoan species, with dung beetles being particularly sensitive. The comparative effects of IVM and MOX on adult dung beetles were assessed for the first time to determine both the physiological sub-lethal symptoms and pre-lethal consequences. Inhibition of antennal response and ataxia were tested as two intuitive and ecologically relevant parameters by obtaining the lowest observed effect concentration (LOEC) values and interpolating other relevant toxicity thresholds derived from concentration-response curves (IC50, as the concentration of each ML where the antennal response is inhibited by half; and pLC50, as the quantity of ingested ML where partial paralysis was observed by half of treated individuals) from concentration-response curves. Both sub-lethal and pre-lethal symptoms obtained in this study coincided in that IVM was six times more toxic than MOX for adult dung beetles. Values of LOEC, IC50 and pLC50 obtained for IVM and MOX evaluated in an environmental context indicate that MOX, despite needing more time for its elimination in the faeces, would be half as harmful to dung beetles as IVM. This approach will be valuable to clarify the real impact of MLs on dung beetle health and to avoid the subsequent environmental consequences

A transcriptomic analysis of gene expression in the venom gland of the snake Bothrops alternatus (urutu)

<p>Abstract</p> <p>Background</p> <p>The genus <it>Bothrops </it>is widespread throughout Central and South America and is the principal cause of snakebite in these regions. Transcriptomic and proteomic studies have examined the venom composition of several species in this genus, but many others remain to be studied. In this work, we used a transcriptomic approach to examine the venom gland genes of <it>Bothrops alternatus</it>, a clinically important species found in southeastern and southern Brazil, Uruguay, northern Argentina and eastern Paraguay.</p> <p>Results</p> <p>A cDNA library of 5,350 expressed sequence tags (ESTs) was produced and assembled into 838 contigs and 4512 singletons. BLAST searches of relevant databases showed 30% hits and 70% no-hits, with toxin-related transcripts accounting for 23% and 78% of the total transcripts and hits, respectively. Gene ontology analysis identified non-toxin genes related to general metabolism, transcription and translation, processing and sorting, (polypeptide) degradation, structural functions and cell regulation. The major groups of toxin transcripts identified were metalloproteinases (81%), bradykinin-potentiating peptides/C-type natriuretic peptides (8.8%), phospholipases A₂(5.6%), serine proteinases (1.9%) and C-type lectins (1.5%). Metalloproteinases were almost exclusively type PIII proteins, with few type PII and no type PI proteins. Phospholipases A₂were essentially acidic; no basic PLA₂were detected. Minor toxin transcripts were related to L-amino acid oxidase, cysteine-rich secretory proteins, dipeptidylpeptidase IV, hyaluronidase, three-finger toxins and ohanin. Two non-toxic proteins, thioredoxin and double-specificity phosphatase Dusp6, showed high sequence identity to similar proteins from other snakes. In addition to the above features, single-nucleotide polymorphisms, microsatellites, transposable elements and inverted repeats that could contribute to toxin diversity were observed.</p> <p>Conclusions</p> <p><it>Bothrops alternatus </it>venom gland contains the major toxin classes described for other <it>Bothrops </it>venoms based on trancriptomic and proteomic studies. The predominance of type PIII metalloproteinases agrees with the well-known hemorrhagic activity of this venom, whereas the lower content of serine proteases and C-type lectins could contribute to less marked coagulopathy following envenoming by this species. The lack of basic PLA₂agrees with the lower myotoxicity of this venom compared to other <it>Bothrops </it>species with these toxins. Together, these results contribute to our understanding of the physiopathology of envenoming by this species.</p

Fluid inclusion depth and thickness estimates using a Na nuclear reaction resonance and Si elastic scattering

International audienceAn important aspect of quantitative fluid inclusion analysis using X-ray emission techniques concerns a knowledge of fluid inclusion depth and geometry to establish reliable absorption correction procedures. The aim of this study is to assess the potential performance of the nuclear reaction 23Na(p, p′γ)23Na in estimating inclusion depth. Na was chosen because of its common occurrence in natural fluids. The nuclear reaction displays a characteristic, low energy resonance peak at 1.283 MeV in its cross-section which, together with recognition that the energy of the incident particles traversing matter decreases predictably with depth, allow estimation of the thickness of quartz traversed by the beam and hence the inclusion depth. Results of the calculation shows accuracy on estimated fluid inclusion depths commonly better than ±0.5 μm. In addition, following the same experimental protocol as defined for Na, we show how the use of the elastic scattering reaction 28Si(p, p)28Si can provide information on the fluid inclusion thickness

Redox heterogeneities in a subducting slab: Example from the Monviso meta-ophiolite (Western Alps, Italy)

International audienceVariations of redox conditions (i.e., oxygen fugacity, fO2) accompanying slab dehydration in subduction zones are subject to ongoing controversies, especially since the interplay between redox sensitive elements during prograde metamorphism remains complex and, likely, variable at the slab scale. Here we investigate fO2 variations during serpentinite dehydration and their feedback on the stability of sulfur and carbon compounds by studying the eclogitic Monviso meta-ophiolite (Western Alps, Italy). Despite a complex metamorphic history, the Monviso massif has preserved a complete section of oceanic lithosphere, from seafloor metasediments, meta-ophicarbonates and metabasites to deep- seated metagabbros and metaserpentinites. By bringing new estimates in the northern massif, we show that these lithologies have recorded a homogeneous pressure and temperature (P-T) climax, at 520-570°C and 2.6-2.7 GPa, on the whole meta-ophiolite. Despite this homogeneous P-T record, serpentinite forming minerals imply strong variations in fO2 according to their position in the slab, from high fO2 conditions (~ FMQ +2) in the deep-seated lithologies made of heazlewoodite-magnetite-olivine assemblages to low fO2 (~ FMQ -4) in the paleoseafloor lithologies made of pentlandite- awaruite-olivine. This redox gradient is opposed to what is expected at mid-ocean ridges and is therefore likely set up during serpentinite dehydration. Such variations of fO2 conditions also influenced carbon distribution and redox state within the lithosphere. In particular, reducing conditions associated with brucite breakdown in paleoseafloor serpentinites promote the formation of disordered carbonaceous matter over inorganic carbonates. Newly-formed disordered carbonaceous matter could subsequently be recycled in the deep mantle, with the potential to play a major role on the deep carbon cycle

Atmospheric CO2 uptake throughout bio-enhanced brucite-water reaction at Montecastelli serpentinites (Italy)

In the last several years, interactions between microorganisms and minerals have intrigued and catched the interest of the scientific community. Montecastelli serpentinites (Tuscany, Italy) are characterized by CO2-mineral carbonation, an important process which leads to spontaneous formation of carbonate phases uptaking atmospheric CO2. In the studied areas carbonate precipitates, mainly hydrated Mg-carbonates, are present in form of crusts, coating and spherules on exposed rock surfaces, and filling rock fractures. Petrographic and mineralogical observations revealed that Tuscan brucite-rich serpentinites hosts preserve their original chemical compositions with typical mesh-textured serpentine ( brucite) after olivine, magnetite-rich mesh rims and relicts of primary spinel. Representative hydrated carbonate samples have been collected in three different areas and analyzed to investigate the role of biological activity and its influence in the serpentine-hydrated Mg-carbonates reaction. The different types of whitish precipitates have been selected under binocular microscope for XRD analyses performed at the Dipartimento di Scienze della Terra (University of Pisa, Italy): their mineralogical composition consists of mainly hydromagnesite and variable amount of other metastable carbonate phases (i.e. nesquehonite, manasseite, pyroaurite, brugnatellite and aragonite). Moreover, the crystallinity analysis of whitish crust and spherules have been carried out by detailed and quantitative XRD analyses to testify a possible biologically controlled growth, inasmuch as the crystal structure of biominerals could be affected by many lattice defects (i.e. dislocations, twinning, etc.) and this observation cause low crystallinity of the mineral. The presence of microbial cells and relicts of organic matter has already been detected by confocal laser scanning microscopy (CLSM) combined with Raman spectromicroscopy in a previous study (Bedini et al., 2013). The presence of active microbial communities in or at the serpentinites surface could promote and/or enhance the key reaction through which serpentine, reacting with the carbon dioxide, becomes hydrated Mg-carbonates. This novel study aims to provide a contribution to the identification of the biominerals that could be a valid proof between CO2-mineral sequestration and microbial activity interactions. This innovative research is designed to provide a plan in future at industrial scale to reduce and capture the greenhouse gas content by Earth’s atmosphere, thanks to the precipitation of carbonate biominerals

Contrasting Cu-complexing behaviour in vapour and liquid fluid inclusions from the Yankee Lode tin deposit, Mole Granite, Australia

International audienceSynchrotron Radiation-induced X-Ray Fluorescence (SR-XRF) and X-ray Absorption Near Edge Structure (XANES) experiments were performed on coexisting low density vapour and high density liquid inclusions from the Yankee Lode, Mole Granite, Australia. The chosen sample is a quartz crystal from a cassiterite–quartz-vein, showing a complex hydrothermal growth history characterized by successive pulses of fluid trapping from 600 to 200 °C. The liquid and vapour inclusions analysed predated cassiterite precipitation and show a homogenisation temperature of about 450 °C. In vapour inclusions, SR-XRF mapping showed that Cu is associated with S together with K, Mn, Fe, Zn and As, likely as a sulphide mineral. Elemental quantification deduced from XRF maps performed at room temperature on heterogeneous and on inclusions homogenised by heating indicate that Cu was concentrated in the low density vapour inclusions whereas Cl, K, Mn, Fe, Zn, Br and Rb were partitioned in the high density liquid phase. S and As show partition coefficients close to 1:1, with As displaying a stronger affinity for the liquid phase than S. Micro-XANES experiments at the Cu Kα edge show that Cl-ligand complexes dominate upon heating in both inclusion types up to 450 °C. SR-XRF mapping during heating revealed that the vapour inclusion was not completely homogenised at 450 °C. XANES analysis of the vapour inclusion showed that a new Cu-bearing phase formed above 450 °C, which is not detectable in the liquid inclusion. To our knowledge, species detected in the XANES spectra acquired at 506 °C do not correspond to any Cu–Cl complex published so far in the literature. We propose that a Cu1+ complex of still unknown stoichimetry, including sulfur as a ligand and possibly Cl as well, could account for Cu complexation at high temperature. This observation supports the hypothesis that sulfur could play a central role for Cu-complexing in high temperature porphyry-type environments. Experimental data in the system Cu–S–Cl–CO2–H2O are needed to document fully this newly discovered Cu complex

Effect of the heterotrophic bacterium Pseudomonas reactans on olivine dissolution kinetics and implications for CO2 storage in basalts

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