Overview of recent TJ-II stellarator results

The main results obtained in the TJ-II stellarator in the last two years are reported. The most important topics investigated have been modelling and validation of impurity transport, validation of gyrokinetic simulations, turbulence characterisation, effect of magnetic configuration on transport, fuelling with pellet injection, fast particles and liquid metal plasma facing components. As regards impurity transport research, a number of working lines exploring several recently discovered effects have been developed: the effect of tangential drifts on stellarator neoclassical transport, the impurity flux driven by electric fields tangent to magnetic surfaces and attempts of experimental validation with Doppler reflectometry of the variation of the radial electric field on the flux surface. Concerning gyrokinetic simulations, two validation activities have been performed, the comparison with measurements of zonal flow relaxation in pellet-induced fast transients and the comparison with experimental poloidal variation of fluctuations amplitude. The impact of radial electric fields on turbulence spreading in the edge and scrape-off layer has been also experimentally characterized using a 2D Langmuir probe array. Another remarkable piece of work has been the investigation of the radial propagation of small temperature perturbations using transfer entropy. Research on the physics and modelling of plasma core fuelling with pellet and tracer-encapsulated solid-pellet injection has produced also relevant results. Neutral beam injection driven Alfvénic activity and its possible control by electron cyclotron current drive has been examined as well in TJ-II. Finally, recent results on alternative plasma facing components based on liquid metals are also presentedThis work has been carried out within the framework of the EUROfusion Consortium and has received funding from the Euratom research and training programme 2014–2018 under Grant Agreement No. 633053. It has been partially funded by the Ministerio de Ciencia, Inovación y Universidades of Spain under projects ENE2013-48109-P, ENE2015-70142-P and FIS2017-88892-P. It has also received funds from the Spanish Government via mobility grant PRX17/00425. The authors thankfully acknowledge the computer resources at MareNostrum and the technical support provided by the Barcelona S.C. It has been supported as well by The Science and Technology Center in Ukraine (STCU), Project P-507F

Conserved linker length in double dsRBD proteins from plants restricts interdomain motion

Double stranded RNA binding domains (dsRBDs) are ubiquitous in all kingdoms of life. They can participate both in RNA and protein recognition and are usually present in multiple copies in multidomain proteins. We analyzed the linkers between dsRBDs in different proteins and found that sequences corresponding to plant proteins have a highly conserved linker length. In order to assess the importance of linker length in the conformational freedom of double dsRBD plant proteins, we introduced lanthanide binding tags (LBTs) in different positions of the dsRBD containing protein HYL1 from Arabidopsis thaliana. These constructs were used to obtain conformational restraints from Double electron–electron resonance (DEER) measurements on doubly labeled proteins and from paramagnetic relaxation enhancement (PRE) in single labeled samples. Fitting the experimental datasets to a computational model of the ensemble created by allowing freedom to the linker region we found that the domains tend to explore a particular region of the allowed conformational space. The high conservation in linker length suggests that this restricted conformational sampling is functional, possibly hindering HYL1-dsRBD2 from contacting the substrate dsRNA and allowing it to participate in protein-protein interactions

Pulse Electron Double Resonance Detected Multinuclear NMR Spectra of Distant and Low Sensitivity Nuclei and Its Application to the Structure of Mn(II) Centers in Organisms.

International audienceThe ability to characterize the structure of metal centers beyond their primary ligands is important to understanding their chemistry. High-magnetic-field pulsed electron double resonance detected NMR (ELDOR-NMR) is shown to be a very sensitive approach to measuring the multinuclear NMR spectra of the nuclei surrounding Mn(II) ions. Resolved spectra of intact organisms with resonances arising from (55)Mn, (31)P, (1)H, (39)K, (35)Cl, (23)Na, and (14)N nuclei surrounding Mn(2+) centers were obtained. Naturally abundant cellular (13)C could be routinely measured as well. The amplitudes of the (14)N and (2)H ELDOR-NMR spectra were found to be linearly dependent on the number of nuclei in the ligand sphere. The evolution of the Mn(II) ELDOR-NMR spectra as a function of excitation time was found to be best described by a saturation phenomenon rather than a coherently driven process. Mn(II) ELDOR-NMR revealed details about not only the immediate ligands to the Mn(II) ions but also more distant nuclei, providing a view of their extended structures. This will be important for understanding the speciation and chemistry of the manganese complexes as well as other metals found in organisms

Using Genetically Encodable Self-Assembling Gd(III) Spin Labels to Make In-cell Nanometric Distance Measurements.

International audienceDouble electron-electron resonance (DEER) can be used to study the structure of a protein in its native cellular environment. Until now, this has required isolation, in vitro labeling, and reintroduction of the protein back into the cells. We describe a completely biosynthetic approach that avoids these steps. It exploits genetically encodable lanthanide-binding tags (LBT) to form self-assembling GdIII metal-based spin labels and enables direct in-cell measurements. This approach is demonstrated using a pair of LBTs encoded one at each end of a 3-helix bundle expressed in E. coli grown on GdIII -supplemented medium. DEER measurements directly on these cells produced readily detectable time traces from which the distance between the GdIII labels could be determined. This work is the first to use biosynthetically produced self-assembling metal-containing spin labels for non-disruptive in-cell structural measurements

Nanometric distance measurements between Mn(II)DOTA centers

International audiencePulse electron-electron double resonance (PELDOR) is a versatile technique for probing the structures and functions of complex biological systems. Despite the recent interest in high-spin metal-ions for high field/frequency applications, PELDOR measurements of Mn(II) remain relatively underexplored. Here we present Mn(II)-Mn(II) PELDOR distance measurements at 94 GHz on polyproline II (PPII) helices doubly spin-labeled with Mn(II) DOTA, which are distinguished by their small zero-field interaction. The measured Mn-Mn distances and distribution profiles were in good agreement with the expected values from molecular models. Additional features in the frequency-domain spectra became apparent at certain combinations of detect and pump frequencies. Spin-Hamiltonian calculations showed that they likely arose from contributions from the pseudo-secular component of the dipolar interaction that were found to be non-negligible for Mn(II) DOTA. However, the influence of the pseudo-secular component on the distance distribution profiles apparently was limited. The results show the potential of Mn(II) DOTA spin labels for high-field PELDOR distance measurements in proteins and other biological systems

DAQ-induced modification on C196 affects SOD2 activity.

<p>The comparison of the residual activity after DAQ-modification indicates that the activity of wt SOD2 and the C140A mutant decreases significantly in the presence of DAQs in a dose-dependent manner. The activity of C196A and C140A/C196A mutants does not show a statistically significant DAQ-dependent effect. Values are the mean ± SD. * p<0.05, § p<0.01, # p<0.001 relative to the protein activities before the reaction with DAQs.</p