Biochemical, kinetic and structural characterization of the unusual GTPase cycle of Roco proteins

Since mutations in the gene coding for the human Roco protein LRRK2 were found to be the most frequent cause of familial Parkinson’s Disease, the protein has been intensively studied. Despite tremendous research efforts, and the discovery of several LRRK2 pathways and interaction partners, still many research questions remain unanswered. One important aspect of the working mechanism of LRRK2 still under debate, is the functioning of the central RocCOR module, responsible for the protein’s GTPase activity. During my PhD research, I have unravelled the GTP hydrolysis mechanism of Roco proteins. In a first part of the study, I investigated the oligomeric state of the bacterial Chlorobium tepidum Roco protein upon nucleotide binding. We could show that the protein cycles between a monomeric and dimeric state upon nucleotide binding and hydrolysis and that monomerization is a characteristic feature of the GTP hydrolysis cycle. In a second part of the study, I have characterized the GTP hydrolysis mechanism of several prokaryotic Roco proteins and human LRRK2 via biochemical and kinetic experiments. I have shown that the hydrolysis itself is the rate-limiting step in the GTP hydrolysis cycle and that Roco proteins do not require auxiliary proteins for the exchange of nucleotides, although additional factors might still regulate the moderate GTPase activity. Based on these data, we have proposed a new working hypothesis for Roco proteins in general and LRRK2 in particular. In this way, this work provides valuable new insights in our endeavour to unravel the working mechanism of this protein family

Voltage mapping and pacing to assess the level of pulmonary venous isolation achieved with a novel circular multielectrode ablation catheter.

Aims The aim of the study was to determine the level of pulmonary vein (PV) isolation achieved with the use of a novel radiofrequency circular multielectrode ablation catheter [pulmonary vein ablation catheter (PVAC)] in patients with paroxysmal atrial fibrillation. Although some efficacy data have been presented, the level of PV isolation, which is crucial both for efficacy and safety of the ablation, has not been defined with this new ablation catheter. Methods and results Detailed sinus rhythm voltage maps using an electroanatomic mapping system and projected on 3D computed tomography-derived reconstructions of the left atrium (LA) were obtained before and after PV isolation with the PVAC. Left atrium–PV entry and exit block was assessed for each vein. The population consisted of 12 patients, mean age 57 ± 6 years, seven male. After ablation, an extensive zone of potential reduction that included the ostium of each PV was observed in all patients. Bipolar voltages were significantly reduced in all PVs and in the LA close to the vein ostia, the mean voltage reduction was >80%. Conclusion Using the PVAC, (i) PVs are isolated at the level of the PV ostium and, importantly, outside the tubular portion and (ii) significant voltage reduction is also recorded at various extent proximal to the PV ostium at the level of the antral region

Discharge initiation by ICRF antenna in IShTAR

IShTAR is a linear magnetized plasma test facility dedicated to the investigation of RF wave/plasma interaction. The IShTAR ICRF system consists of a single strap RF antenna. When using the antenna for plasma production without an external plasma source, it is shown that the plasma is either produced in front of the antenna strap or inside the antenna box depending on the antenna parameters. Here, we present experimental and numerical investigation of the plasma initiation parametric dependencies. Detailed pressure and RF power scans were performed in helium at f = 5.22 MHz and f = 42.06 MHz. The experiment shows the parameter ranges for which the plasma is produced in front of the strap, or inside the antenna box. These ranges are validated by simulations with the RFdinity model, and by theoretical predictions

Correlation analysis for energy losses, waiting times and durations of type I edge-localized modes in the Joint European Torus

Several important ELM control techniques are in large part motivated by the empirically observed inverse relationship between average ELM energy loss and ELM frequency in a plasma. However, to ensure a reliable effect on the energy released by the ELMs, it is important that this relation is verified for individual ELM events. Therefore, in this work the relation between ELM energy loss (W-ELM) and waiting time (Delta t(ELM)) is investigated for individual ELMs in a set of ITER-like wall plasmas in JET. A comparison is made with the results from a set of carbon-wall and nitrogen-seeded ITER-like wall JET plasmas. It is found that the correlation between W-ELM and Delta t(ELM) for individual ELMs varies from strongly positive to zero. Furthermore, the effect of the extended collapse phase often accompanying ELMs from unseeded JET ILW plasmas and referred to as the slow transport event (STE) is studied on the distribution of ELM durations, and on the correlation between W-ELM and Delta t(ELM). A high correlation between W-ELM and Delta t(ELM), comparable to CW plasmas is only found in nitrogen-seeded ILW plasmas. Finally, a regression analysis is performed using plasma engineering parameters as predictors for determining the region of the plasma operational space with a high correlation between W-ELM and Delta t(ELM)