The Cylindrical GEM-Inner Tracker (CGEM-IT) is the upgrade of the internal tracking system of the BESIII experiment. It consists of three layers of cylindrically-shaped triple GEMs, with important ...innovations with respect to the existing GEM detectors, in order to achieve the best performance with the lowest material budget. It will be the first cylindrical GEM running with analog readout inside a 1T magnetic field. The simultaneous measurement of both the deposited charge and the signal time will permit to use a combination of two algorithms to evaluate the spatial position of the charged tracks inside the CGEM-IT: the charge centroid and the micro time projection chamber modes. They are complementary and can cope with the asymmetry of the electron avalanche when running in magnetic field and with non-orthogonal incident tracks. To evaluate the behaviour under different working settings, both planar chambers and the first cylindrical prototype have been tested during various test beams at CERN with 150 GeV/
c
muons and pions. This paper reports the results obtained with the two reconstruction methods and a comparison between the planar and cylindrical chambers.
Lactate dehydrogenase (LDH) catalyzes the conversion of pyruvate to lactate with concomitant oxidation of NADH during the last step in anaerobic glycolysis. In the present study, we present a ...comparative biochemical and structural analysis of various LDHs adapted to function over a large temperature range. The enzymes were from
Champsocephalus gunnari (an Antarctic fish),
Deinococcus radiodurans (a mesophilic bacterium) and
Thermus thermophilus (a hyperthermophilic bacterium). The thermodynamic activation parameters of these LDHs indicated that temperature adaptation from hot to cold conditions was due to a decrease in the activation enthalpy and an increase in activation entropy. The crystal structures of these LDHs have been solved. Pairwise comparisons at the structural level, between hyperthermophilic
versus mesophilic LDHs and mesophilic
versus psychrophilic LDHs, have revealed that temperature adaptation is due to a few amino acid substitutions that are localized in critical regions of the enzyme. These substitutions, each having accumulating effects, play a role in either the conformational stability or the local flexibility or in both. Going from hot- to cold-adapted LDHs, the various substitutions have decreased the number of ion pairs, reduced the size of ionic networks, created unfavorable interactions involving charged residues and induced strong local disorder. The analysis of the LDHs adapted to extreme temperatures shed light on how evolutionary processes shift the subtle balance between overall stability and flexibility of an enzyme.
The PANDA spectrometer will be built at the FAIR facility at Darmstadt (Germany) to perform accurate tests of the strong interaction through pp and pA annihilation studies. The charged particle ...tracking at PANDA will be done using both solid state and gaseous detectors. Among the latter, two straw tube detector systems will be built 1, The cylindrical, central straw tube tracker features a high spatial and momentum resolution for a wide range of particle momenta from about 8 GeV/c down to a few 100 MeV/c, together with particle identification in the momentum region below about 1 GeV/c by measuring the specific energy-loss, A new technique, based on self-supporting straw double layers with intrinsic wire tension developed for the COSY-TOF straw tracker 2, has been adopted for the PANDA trackers. The development of the readout electronics for the straw tubes is ongoing. Prototypes have been produced and used to instrument straw tube modules that have been tested with cosmic rays and proton beams. Design issues of the PANDA straw tubes, together with the results of the prototype tests are presented.
Nudix pyrophosphatases are a well represented protein family in the Deinococcus radiodurans genome. These hydrolases, which are known to be enzymatically active towards nucleoside diphosphate ...derivatives, play a role in cleansing the cell pool of potentially deleterious damage products. Here, the structure of DR2204, the only ADP‐ribose pyrophosphatase in the D. radiodurans genome that is known to be active towards flavin adenosine dinucleotide (FAD), is presented at 2.0 Å resolution.
A cylindrical GEM detector with analog readout is under development for the upgrade of the Inner Tracker of the BESIII experiment at IHEP (Beijing). The new detector will match the requirements for ...momentum resolution (σpt/pt~0.5% at 1GeV) and radial resolution (σxy~120μm) of the existing drift chamber and will improve significantly the spatial resolution along the beam direction (σz~150μm) with very small material budget (less than 1.5% of X0). With respect to the state of the art the following innovations will be deployed: a lighter mechanical structure based on Rohacell, a new XV anode readout plane with jagged strip layout to reduce the parasitic capacitance, and the use of the analogue readout inside a high intensity magnetic field to have good spatial resolution without increasing the number of channels.
Tuberculosis (TB) is the primary cause of mortality among infectious diseases. Mycobacterium tuberculosis thymidylate kinase (TMPK(Mtub)) catalyzes the ATP-dependent phosphorylation of deoxythymidine ...5'-monophosphate (dTMP). Essential to DNA replication, this enzyme represents a promising target for developing new drugs against TB, because the configuration of its active site is unique within the TMPK family. Indeed, it has been proposed that, as opposed to other TMPKs, catalysis by TMPK(Mtub) necessitates the transient binding of a magnesium ion coordinating the phosphate acceptor. Moreover, 3'-azidodeoxythymidine monophosphate (AZTMP) is a competitive inhibitor of TMPK(Mtub), whereas it is a substrate for human and other TMPKs. Here, the crystal structures of TMPK(Mtub) in complex with deoxythymidine (dT) and AZTMP were determined to 2.1 and 2.0 A resolution, respectively, and suggest a mechanism for inhibition. The azido group of AZTMP perturbs the induced-fit mechanism normally adopted by the enzyme. Magnesium is prevented from binding, and the resulting electrostatic environment precludes phosphoryl transfer from occurring. Our data provide a model for drug development against tuberculosis.
PDF
