Partial melting as an efficient mechanism to produce rare metal granite?

<p>Rare metal (HFSE such Sn, W, Ta, Nb and LILLE such Li, Rb) granite represent the most enriched magmatic rocks on Earth. This is especially true for some elements that belongs either to the European list of critical raw materials and/or the conflict minerals (eg. Li, Sn, W, Nb, Ta). Rare metal granites generally emplace in the vincinity of S-type granites during late orogenic stages. The fraction crystallisation mechanism is postulated to be the unique way to produce enriched silicate melt that later leads to ore deposits due to a combination of magmatic/hydrothermal processes. However, some problems persist in the explanation of the genesis of rare metal granite: crystal fractionation alone does not lead to the very high rare metal concentrations; field discrepancies exist between rare metal granites and their supposed parent peraluminous granites that in some cases are unknown. An alternative model - based on the integration of geochemical, experimental, paleogeographical and structural studies – suggests that low degree partial melting could be an efficient mechanism to produce critical metals enriched silicate melts enriched. To test whether this hypothesis makes sense, we present a study of the behaviour of W, Sn, Nb and Ta in metamorphic minerals from various metapelitic rocks. The selected samples do not present anomalous bulk concentrations of these elements with respect to an average continental crust. They formed at different pressure temperature conditions, in different orogenic belts. The rock collection comprises (i) amphibolite-facies staurolite bearing rocks, (ii) sillimanite-bearing rocks and (iii) granulite-facies orthopyroxene-bearing rocks. These samples represent the three main stages of the classical evolution of a collisional gradient leading to partial melting: they respectively belong to the muscovite + biotite domain, the muscovite-out reaction and the biotite-out reaction. We first estimate pressure-temperature conditions of formation of the rocks using pseudosection modelling. We then expose a set of LA-ICP-MS data to identify the critical metal carriers minerals in our samples. Meanwhile, we investigate the behaviour of W, Sn, Nb and Ta during the muscovite out reaction with two piston cylinder experiments (a partial melting experiment and a crystallization experiment). The protolith consists of a staurolite-bearing metapelite that did not suffer partial melting. In the light of these new data, we discuss the framework of the production of critical metal enriched silicate melts. We show that the main carrier of W is muscovite (up to 30 ppm) and that biotite handle Sn at high temperature (up to 40ppm). Using both the data from the natural sample and the experiments, we highlight that muscovite releases W during its destabilisation ant that Sn enters in biotite until the mineral breaks. We finally discuss the implication of multiple low degree partial melting / melt extraction as efficient way to produce enriched silicate melts.</p>

IceBear: an intuitive and versatile web application for research-data tracking from crystallization experiment to PDB deposition

The web-based IceBear software is a versatile tool to monitor the results of crystallization experiments and is designed to facilitate supervisor and student communications. It also records and tracks all relevant information from crystallization setup to PDB deposition in protein crystallography projects. Fully automated data collection is now possible at several synchrotrons, which means that the number of samples tested at the synchrotron is currently increasing rapidly. Therefore, the protein crystallography research communities at the University of Oulu, Weizmann Institute of Science and Diamond Light Source have joined forces to automate the uploading of sample metadata to the synchrotron. In IceBear, each crystal selected for data collection is given a unique sample name and a crystal page is generated. Subsequently, the metadata required for data collection are uploaded directly to the ISPyB synchrotron database by a shipment module, and for each sample a link to the relevant ISPyB page is stored. IceBear allows notes to be made for each sample during cryocooling treatment and during data collection, as well as in later steps of the structure determination. Protocols are also available to aid the recycling of pins, pucks and dewars when the dewar returns from the synchrotron. The IceBear database is organized around projects, and project members can easily access the crystallization and diffraction metadata for each sample, as well as any additional information that has been provided via the notes. The crystal page for each sample connects the crystallization, diffraction and structural information by providing links to the IceBear drop-viewer page and to the ISPyB data-collection page, as well as to the structure deposited in the Protein Data Bank.

Boundary Layer Description of Directional Polymer Crystallisation

Nearly fifty years ago Lovinger and Gryte suggested that the directional crystallization of a polymer was analogous to the quiescent isothermal crystallization experiment but at a supercooling where the crystal...

Crystallization and preliminary X-ray diffraction studies of melibiose permease

Our work presented here showed that MelB can be crystallized in the conditions as similar as that of other membrane transporter protein of known structure. To identify a rigid protein by modifying the protein structure is the critical factor for facilitating MelB crystallization. It is necessary to perform extensive crystallization screens to obtain crystals. MelB-MelB interaction in the DDM containing solution will be affect by protein preparation, which may lead to reduce in reproducibility of crystallization experiment. Using a detergent mixture is essential for improve protein contact in the crystals, then improve crystallizability. R149C MelB crystal can be obtained in DDM, but these crystals were only diffracted to about 8Å resolution limit. MelB wide type crystal also can be obtained from the condition as that of R149C mutant, but the resolution is weaker than that of mutant. Although MelB and other transporters of known structure share common feature of the crystallization, the emphasis was as much on the protein itself, as it was on detergent type or efficient screening and refinement of the crystallization conditions.

Optimization of crystallization of biological macromolecules using dialysis combined with temperature control

A rational way to find the appropriate conditions to grow crystal samples for bio-crystallography is to determine the crystallization phase diagram, which allows precise control of the parameters affecting the crystal growth process. First, the nucleation is induced at supersaturated conditions close to the solubility boundary between the nucleation and metastable regions. Then, crystal growth is further achieved in the metastable zone – which is the optimal location for slow and ordered crystal expansion – by modulation of specific physical parameters. Recently, a prototype of an integrated apparatus for the rational optimization of crystal growth by mapping and manipulating temperature–precipitant–concentration phase diagrams has been constructed. Here, it is demonstrated that a thorough knowledge of the phase diagram is vital in any crystallization experiment. The relevance of the selection of the starting position and the kinetic pathway undertaken in controlling most of the final properties of the synthesized crystals is shown. The rational crystallization optimization strategies developed and presented here allow tailoring of crystal size and diffraction quality, significantly reducing the time, effort and amount of expensive protein material required for structure determination.

Strange polymorphs and where to find them: a melt inclusion story

<p>Small portions of pristine melt with diameters of 2 to 50µm are increasingly recognized as a rather common occurrence in high grade metamorphic terranes which experienced melting. Their study delivers crucial chemical information on partial melts at depth. But they are also unique "natural experimental charges" where the behaviour of the silicate melt can be investigated, directly in the natural rocks, under P-T-t conditions which cannot be completely reproduced in the laboratory.</p><p>Each nanogranitoid case study has consistently shown H<sub>2</sub>O-bearing, silica and alkali-rich melt. However, rather than a classic granitoid assemblage consisting mainly of quartz and feldspar(s), on cooling these isolated melt droplets produce a plethora of mineral phases identified via microRaman spectroscopy that are rarely –or never- observed as rock-forming minerals. Cristobalite (tetragonal) and tridymite (orthorhombic) are often present as SiO<sub>2</sub> polymorphs, and hexagonal kokchetavite as a polymorph of KAlSi<sub>3</sub>O<sub>8</sub>. NaAlSi<sub>3</sub>O<sub>8</sub> occurs as orthorhombic kumdykolite, whereas CaAl<sub>2</sub>Si<sub>2</sub>O<sub>8 </sub>may occur either as monoclinic svyatoslavite or trigonal dmisteinbergite. Two presently unidentified phases have been also recognized via Raman and analysed via electron microprobe. One has the main peak at 426-430 cm<sup>-1</sup> and has the composition of a granitic glass, whereas the second has a main peak at 412 cm<sup>-1</sup> and a variable composition depending on the inclusion in which it occurs. As their main peaks occur in the same region of most tectosilicates, it is likely that they are two new polymorphs of feldspar, to the best of our knowledge never reported before. These polymorphs have been so far identified in inclusions mainly hosted in garnet, zircon and, in one case, sapphirine and trapped under an extremely variable range of metamorphic conditions (from low P migmatites to UHP eclogites) in very different rock types (metagranitoids, metasediments, mafic and ultramafic rocks).</p><p>Microstructures confirm that all of these phases crystallize directly from the trapped melt on cooling, independently of the internal P of the inclusions or the original conditions of melt entrapment. They appear to be the result of metastability in the inclusions, possibly during rapid crystallization of a melt, not caused by rapid cooling but by the peculiar undercooled and supersaturated conditions achieved on cooling by a melt confined in a small cavity (Ferrero & Angel, 2018). According to this possibility, these polymorphs can be regarded as kinetically stabilized, yet possibly thermodynamically metastable, phases as recently proposed by Zolotarev et al. (2019) for dmisteinbergite. A preliminary crystallization experiment on a haplogranitic melt at undercooled conditions however failed to reproduce such phases. Another possibility is that under natural cooling the confined inclusions experience underpressurization, and the system (i.e. the trapped melt) reacts crystallizing phases, i.e. the polymorphs, less dense than their common counterparts. This would result in the decreasing of the P gradient between inclusions and surrounding rock, equivalent to reducing the free energy of the system.</p><p>References</p><p>Ferrero, S. & Angel, R. 2018. JPet 59, 1671–1700.</p><p>Zolotarev, A.A. et al. 2019. Minerals  9, 570.</p>

Comparison of a retroviral protease in monomeric and dimeric states

Retroviral proteases (RPs) are of high interest owing to their crucial role in the maturation process of retroviral particles. RPs are obligatory homodimers, with a pepsin-like active site built around two aspartates (in DTG triads) that activate a water molecule, as the nucleophile, under two flap loops. Mason–Pfizer monkey virus (M-PMV) is unique among retroviruses as its protease is also stable in the monomeric form, as confirmed by an existing crystal structure of a 13 kDa variant of the protein (M-PMV PR) and its previous biochemical characterization. In the present work, two mutants of M-PMV PR, D26N and C7A/D26N/C106A, were crystallized in complex with a peptidomimetic inhibitor and one mutant (D26N) was crystallized without the inhibitor. The crystal structures were solved at resolutions of 1.6, 1.9 and 2.0 Å, respectively. At variance with the previous study, all of the new structures have the canonical dimeric form of retroviral proteases. The protomers within a dimer differ mainly in the flap-loop region, with the most extreme case observed in the apo structure, in which one flap loop is well defined while the other flap loop is not defined by electron density. The presence of the inhibitor molecules in the complex structures was assessed using polder maps, but some details of their conformations remain ambiguous. In all of the presented structures the active site contains a water molecule buried deeply between the Asn26-Thr27-Gly28 triads of the protomers. Such a water molecule is completely unique not only in retropepsins but also in aspartic proteases in general. The C7A and C106A mutations do not influence the conformation of the protein. The Cys106 residue is properly placed at the homodimer interface area for a disulfide cross-link, but the reducing conditions of the crystallization experiment prevented S—S bond formation. An animated Interactive 3D Complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:Acta_Cryst_D:S2059798319011355.

Iterative screen optimization maximizes the efficiency of macromolecular crystallization

Advances in X-ray crystallography have streamlined the process of determining high-resolution three-dimensional macromolecular structures. However, a rate-limiting step in this process continues to be the generation of crystals that are of sufficient size and quality for subsequent diffraction experiments. Here, iterative screen optimization (ISO), a highly automated process in which the precipitant concentrations of each condition in a crystallization screen are modified based on the results of a prior crystallization experiment, is described. After designing a novel high-throughput crystallization screen to take full advantage of this method, the value of ISO is demonstrated by using it to successfully crystallize a panel of six diverse proteins. The results suggest that ISO is an effective method to obtain macromolecular crystals, particularly for proteins that crystallize under a narrow range of precipitant concentrations.

A novel bacterial class V dye-decolourizing peroxidase from the extremophile Deinococcus radiodurans: cloning, expression optimization, purification, crystallization, initial characterization and X-ray diffraction analysis

Deinococcus radiodurans is a bacterium with extreme resistance to desiccation and radiation. The resistance mechanism is unknown, but an efficient reactive oxygen species (ROS) scavenging system and DNA-repair and DNA-protection mechanisms are believed to play important roles. Here, the cloning and small- and medium-scale expression tests of a novel dye-decolourizing peroxidase from D. radiodurans (DrDyP) using three different Escherichia coli strains and three different temperatures in order to identify the optimum conditions for the expression of recombinant DrDyP are presented. The best expression conditions were used for large-scale expression and yielded ∼10 mg recombinant DrDyP per litre of culture after purification. Initial characterization experiments demonstrated unusual features with regard to the haem spin state, which motivated the crystallization experiment. The obtained crystals were used for data collection and diffracted to 2.2 Å resolution. The crystals belonged to the trigonal space group P31 or P32, with unit-cell parameters a = b = 64.13, c = 111.32 Å, and are predicted to contain one DrDyP molecule per asymmetric unit. Structure determination by molecular replacement using previously determined structures of dye-decolourizing peroxidases with ∼30% sequence identity at ∼2 Å resolution as templates are ongoing.

Effect of the weather conditions during solution preparation on lysozyme crystallization

Protein crystallization is a delicate process that is always sensitive to environmental factors. When the environmental factors are not well controlled or not controlled at all, identical crystallization droplets from the same mother liquid may yield different crystallization results. One environmental factor, the weather conditions during crystallization solution preparation, is not usually considered as a parameter for protein crystallization. In this paper, it is shown that the weather parameters during preparation of the crystallization experiment, including the ambient temperature, humidity, pressure and particulate matter in the air, can all affect the reproducibility of lysozyme crystallization. An identical lysozyme crystallization experiment was repeated for an entire year, and the weather conditions when each crystallization experiment was set up were recorded along with the crystallization results. Among the parameters recorded, the humidity during the experiment setup showed the strongest effect on lysozyme crystallization. On the basis of these results, it is suggested that the weather conditions during crystallization solution preparation should be considered as a potential factor that can influence protein crystallization.