An astrocyte-dependent mechanism for neuronal rhythmogenesis

Communication between neurons rests on their capacity to change their firing pattern to encode different messages. For several vital functions, such as respiration and mastication, neurons need to generate a rhythmic firing pattern. Here we show in the rat trigeminal sensori-motor circuit for mastication that this ability depends on regulation of the extracellular Ca2+ concentration ([Ca2+]e) by astrocytes. In this circuit, astrocytes respond to sensory stimuli that induce neuronal rhythmic activity, and their blockade with a Ca2+ chelator prevents neurons from generating a rhythmic bursting pattern. This ability is restored by adding S100b, an astrocytic Ca2+-binding protein, to the extracellular space, while application of an anti-S100b antibody prevents generation of rhythmic activity. These results indicate that astrocytes regulate a fundamental neuronal property: the capacity to change firing pattern. These findings may have broad implications for many other neural networks whose functions depend on the generation of rhythmic activity

Crystal structure of two new bifunctional nonsubstrate type thrombin inhibitors complexed with human alpha-thrombin.

The crystal structures of two new thrombin inhibitors, P498 and P500, complexed with human alpha-thrombin have been determined at 2.0 A resolution and refined to crystallographic R-factors of 0.170 and 0.169, respectively. These compounds, with picomolar binding constants, belong to a family of potent bifunctional inhibitors that bind thrombin at two remote sites: the active site and the fibrinogen recognition exosite (FRE). The inhibitors incorporate a nonsubstrate type active site binding fragment: Dansyl-Arg-(D)Pipecolic acid (Dns-Arg-(D)Pip), reminiscent of the active-site directed inhibitors MD-805 and MQPA, rendering them resistant to thrombin-induced hydrolysis. The FRE binding fragment of these inhibitors corresponds to the hirudin55-65 sequence. They differ in the chemical nature of the nonpeptidyl linker bridging these two functional activities. In both cases, the active site binding fragment is well defined in the electron density. The DnsH1, ArgH2, and (D)PipH3 groups occupy the S3, S1, and S2 subsites of thrombin, respectively, in a way similar to that observed in the thrombin-MQPA complexes. Binding in the active site of thrombin is characterized by numerous van der Waals contacts and ring-ring system interactions. Unlike in the substrate-like inhibitors, ArgH2 enters the S1 specificity pocket from the P2 position and adopts a bent conformation to make an hydrogen bond to the carboxylate of Asp189. In this noncanonical position, its carbonyl points away from the oxyanion hole, which is now occupied by well-ordered solvent molecules. The linkers fit in the groove extending from the active site to the FRE. The C-terminal fragments of both inhibitors bind in the same way as analogous FRE binding elements in previously described complexes

Fontes convectivas tropicais em um modelo baroclinico espectral global usando funcoes de HOUGH

A fully spectral baroclinic model based on Hough Functions is used to study the influence of the tropical convective heat sources over South America. The sources are stabilished using analytical aproximation to an outgoing longwave radiation climatological data for summer. It is analysed the energy exchange between vertical and horizontal modes

Chemical screening identifies ATM as a target for alleviating senescence

Senescence, defined as irreversible cell-cycle arrest, is the main driving force of aging and age-related diseases. Here, we performed high-throughput screening to identify compounds that alleviate senescence and identified the ataxia telangiectasia mutated (ATM) inhibitor KU-60019 as an effective agent. To elucidate the mechanism underlying ATM's role in senescence, we performed a yeast two-hybrid screen and found that ATM interacted with the vacuolar ATPase V-1 subunits ATP6V1E1 and ATP6V1G1. Specifically, ATM decreased E-G dimerization through direct phosphorylation of ATP6V1G1. Attenuation of ATM activity restored the dimerization, thus consequently facilitating assembly of the V-1 and V-0 domains with concomitant reacidification of the lysosome. In turn, this reacidification induced the functional recovery of the lysosome/autophagy system and was coupled with mitochondrial functional recovery and metabolic reprogramming. Together, our data reveal a new mechanism through which senescence is controlled by the lysosomal-mitochondrial axis, whose function is modulated by the fine-tuning of ATM activity.

Structure of the vacuolar-type ATPase from Saccharomyces cerevisiae at 11-Å resolution

Vacuolar-type ATPases (V-type ATPases) in eukaryotic cells are large membrane protein complexes that acidify various intracellular compartments. The enzymes are regulated by dissociation of the V(1) and V(O) regions of the complex. Here we present the structure of the Saccharomyces cerevisiae V-type ATPase at 11-Å resolution by cryo-EM of protein particles in ice. The structure explains many cross-linking and protein interaction studies. Docking of crystal structures suggests that inhibition of ATPase activity by the dissociated V(1) region involves rearrangement of the N- and C-terminal domains of subunit H and also suggests how this inhibition is triggered upon dissociation. We provide support for this model by demonstrating that mutation of subunit H to increase the rigidity of the linker between its two domains decreases its ability to inhibit ATPase activity.We thank V. Kanelis for advice on rigidifying the subunit H linker region and V. Kanelis, P. Rosenthal, E. Kunji and R. Henderson for discussions and a critical reading of this manuscript. Computations were done on the general-purpose cluster supercomputer at the SciNet High Performance Computing Consortium. J.L.R. was supported by a New Investigator Award from the Canadian Institutes of Health Research (CIHR) and an Early Researcher Award from the Ontario Ministry of Research and Innovation. This research was funded by operating grant MOP 81294 to J.L.R. from the CIHR