Idiosyncratic features in tRNAs participating in bacterial cell wall synthesis

The FemXWv aminoacyl transferase of Weissella viridescens initiates the synthesis of the side chain of peptidoglycan precursors by transferring l-Ala from Ala-tRNAAla to UDP-MurNAc-pentadepsipeptide. FemXWv is an attractive target for the development of novel antibiotics, since the side chain is essential for the last cross-linking step of peptidoglycan synthesis. Here, we show that FemXWv is highly specific for incorporation of l-Ala in vivo based on extensive analysis of the structure of peptidoglycan. Comparison of various natural and in vitro-transcribed tRNAs indicated that the specificity of FemXWv depends mainly upon the sequence of the tRNA although additional specificity determinants may include post-transcriptional modifications and recognition of the esterified amino acid. Site-directed mutagenesis identified cytosines in the G1–C72 and G2–C71 base pairs of the acceptor stem as critical for FemXWv activity in agreement with modeling of tRNAAla in the catalytic cavity of the enzyme. In contrast, semi-synthesis of Ala-tRNAAla harboring nucleotide substitutions in the G3–U70 wobble base pair showed that this main identity determinant of alanyl-tRNA synthetase is non-essential for FemXWv. The different modes of recognition of the acceptor stem indicate that specific inhibition of FemXWv could be achieved by targeting the distal portion of tRNAAla for the design of substrate analogues

Trials

Background The risk/benefit ratio of using statins for primary prevention of cardiovascular (CV) events in elderly people has not been established. The main objectives of the present study are to assess the cost-effectiveness of statin cessation and to examine the non-inferiority of statin cessation in terms of mortality in patients aged 75 years and over, treated with statins for primary prevention of CV events. Methods The “Statins in the elderly” (SITE) study is an ongoing 3-year follow-up, open-label comparative multi-centre, randomized clinical trial that is being conducted in two parallel groups in outpatient primary care offices. Participants meeting the following criteria are included: people aged 75 years and older being treated with statins as primary prevention for CV events, who provide informed consent. After randomization, patients in the statin-cessation strategy are instructed to withdraw their treatment. In the comparison strategy, patients continue their statin treatment at the usual dosage. The cost-effectiveness of the statin-cessation strategy compared to continuing statins will be estimated through the incremental cost per quality-adjusted life years (QALYs) gained at 36 months, from the perspective of the French healthcare system. Overall mortality will be the primary clinical endpoint. We assumed that the mortality rate at 3 years will be 15%. The sample size was computed to achieve 90% power in showing the non-inferiority of statin cessation, assuming a non-inferiority margin of 5% of the between-group difference in overall mortality. In total, the SITE study will include 2430 individuals. Discussion There is some debate on the value of statins in people over 75 years old, especially for primary prevention of CV events, due to a lack of evidence of their efficacy in this population, potential compliance-related events, drug-drug interactions and side effects that could impair quality of life. Data from clinical trials guide the initiation of medication therapy for primary or secondary prevention of CV disease but do not define the timing, safety, or risks of discontinuing the agents. The SITE study is one of the first to examine whether treatment cessation is a cost-effective and a safe strategy in people of 75 years and over, formerly treated with statins

A chemical survey of exoplanets with ARIEL

Thousands of exoplanets have now been discovered with a huge range of masses, sizes and orbits: from rocky Earth-like planets to large gas giants grazing the surface of their host star. However, the essential nature of these exoplanets remains largely mysterious: there is no known, discernible pattern linking the presence, size, or orbital parameters of a planet to the nature of its parent star. We have little idea whether the chemistry of a planet is linked to its formation environment, or whether the type of host star drives the physics and chemistry of the planet’s birth, and evolution. ARIEL was conceived to observe a large number (~1000) of transiting planets for statistical understanding, including gas giants, Neptunes, super-Earths and Earth-size planets around a range of host star types using transit spectroscopy in the 1.25–7.8 μm spectral range and multiple narrow-band photometry in the optical. ARIEL will focus on warm and hot planets to take advantage of their well-mixed atmospheres which should show minimal condensation and sequestration of high-Z materials compared to their colder Solar System siblings. Said warm and hot atmospheres are expected to be more representative of the planetary bulk composition. Observations of these warm/hot exoplanets, and in particular of their elemental composition (especially C, O, N, S, Si), will allow the understanding of the early stages of planetary and atmospheric formation during the nebular phase and the following few million years. ARIEL will thus provide a representative picture of the chemical nature of the exoplanets and relate this directly to the type and chemical environment of the host star. ARIEL is designed as a dedicated survey mission for combined-light spectroscopy, capable of observing a large and well-defined planet sample within its 4-year mission lifetime. Transit, eclipse and phase-curve spectroscopy methods, whereby the signal from the star and planet are differentiated using knowledge of the planetary ephemerides, allow us to measure atmospheric signals from the planet at levels of 10–100 part per million (ppm) relative to the star and, given the bright nature of targets, also allows more sophisticated techniques, such as eclipse mapping, to give a deeper insight into the nature of the atmosphere. These types of observations require a stable payload and satellite platform with broad, instantaneous wavelength coverage to detect many molecular species, probe the thermal structure, identify clouds and monitor the stellar activity. The wavelength range proposed covers all the expected major atmospheric gases from e.g. H2O, CO2, CH4 NH3, HCN, H2S through to the more exotic metallic compounds, such as TiO, VO, and condensed species. Simulations of ARIEL performance in conducting exoplanet surveys have been performed – using conservative estimates of mission performance and a full model of all significant noise sources in the measurement – using a list of potential ARIEL targets that incorporates the latest available exoplanet statistics. The conclusion at the end of the Phase A study, is that ARIEL – in line with the stated mission objectives – will be able to observe about 1000 exoplanets depending on the details of the adopted survey strategy, thus confirming the feasibility of the main science objectives.Peer reviewedFinal Published versio

Male-specific deficits in natural reward learning in a mouse model of neurodevelopmental disorders

Neurodevelopmental disorders, including autism spectrum disorders, are highly male biased, but the underpinnings of this are unknown. Striatal dysfunction has been strongly implicated in the pathophysiology of neurodevelopmental disorders, raising the question of whether there are sex differences in how the striatum is impacted by genetic risk factors linked to neurodevelopmental disorders. Here we report male-specific deficits in striatal function important to reward learning in a mouse model of 16p11.2 hemideletion, a genetic mutation that is strongly associated with the risk of neurodevelopmental disorders, particularly autism and attention-deficit hyperactivity disorder. We find that male, but not female, 16p11.2 deletion animals show impairments in reward-directed learning and maintaining motivation to work for rewards. Male, but not female, deletion animals overexpress mRNA for dopamine receptor 2 and adenosine receptor 2a in the striatum, markers of medium spiny neurons signaling via the indirect pathway, associated with behavioral inhibition. Both sexes show a 50% reduction of mRNA levels of the genes located within the 16p11.2 region in the striatum, including the kinase extracellular-signal related kinase 1 (ERK1). However, hemideletion males show increased activation in the striatum for ERK1, both at baseline and in response to sucrose, a signaling change associated with decreased striatal plasticity. This increase in ERK1 phosphorylation is coupled with a decrease in the abundance of the ERK phosphatase striatum-enriched protein-tyrosine phosphatase in hemideletion males. In contrast, females do not show activation of ERK1 in response to sucrose, but notably hemideletion females show elevated protein levels for ERK1 as well as the related kinase ERK2 over what would be predicted by mRNA levels. These data indicate profound sex differences in the impact of a genetic lesion linked with neurodevelopmental disorders, including mechanisms of male-specific vulnerability and female-specific resilience impacting intracellular signaling in the brain

Identification de facteurs modulant le repliement de la glycoprotéine du virus rabique

Rabies virus (VR) glycoprotein (G) forms spicules at the surface of virions. These spicules have the shape of a globular mass at the tip of a rod. They ensure the attachment of the VR to its target cell and, following the endocytosis of the VR, the protonation of G causes conformational rearrangements which cause the membrane of the virus to merge with that of the cell.The folding of G ectodomain was studied along two axes. The first consisted in characterizing the effect of the transmembrane anchoring domain (DTM) on the structure of the ectodomain of G during its biosynthesis. Different types of membrane anchors have been attached to the ectodomain and ectodomain structure has been probed using monoclonal antibodies. This has allowed us to show that the DTM ensures an optimal distance between the ectodomain and the membrane, otherwise, the protein folds into an alternative form. We thus suggest that a segment of G ectodomain interacts with the membrane and that this interaction is necessary for native folding.In addition, motifs whose mutation also causes alternative folding have been identified in the juxtamembrane region (His-Pro / 397-398 and Asp-Glu-Ala-Glu-Asp / 410-414). The second axis of the structural study of G consisted in analyzing the structure of two peptides corresponding to this region, produced in bacteria, using different spectroscopic techniques. This study has shown that their structure depends on external factors. It could be another region of the protein and / or the membrane.In the third part, a test allowing to follow the fusion of transfected cells was developed. This has supported the functional characterization of all the mutants produced and to specify the role of different domains of G in the membrane fusion process.La glycoprotéine (G) du virus rabique (VR) forme des spicules à la surface des virions. Ces spicules ont la forme d'une masse globulaire portée par une tige. Elles assurent l'attachement du VR à sa cellule cible et, à la suite de l'endocytose du VR, la protonation de G entraîne des réarrangements conformationnels qui provoquent la fusion de la membrane du virus avec celle de la cellule.Le repliement de l'ectodomaine de G a été étudié selon deux axes. Le premier a consisté à caractériser l'effet du domaine d'ancrage transmembranaire (DTM) sur la structure de l'ectodomaine de G lors de sa biosynthèse. Différents types d'ancrage à la membrane ont été attachés à l'ectodomaine et la structure de celui-ci a été caractérisée à l'aide d'anticorps monoclonaux. Cela nous a permis de montrer que le rôle du DTM est d'assurer une distance optimale entre l'ectodomaine et la membrane, faute de quoi, la protéine se replie sous une forme alternative. Nous en avons déduit qu'un segment de l'ectodomaine de G interagit avec la membrane et que cette interaction est nécessaire pour l'acquisition de sa conformation native.Par ailleurs des motifs dont la mutation provoque aussi un repliement alternatif ont été identifiés dans la région juxtamembranaire (His-Pro/397-398 et Asp-Glu-Ala-Glu-Asp/410-414). Le deuxième axe de l'étude structurale de G a consisté à analyser la structure de deux peptides correspondant à cette région, produits en bactéries, à l'aide de différentes techniques spectroscopiques. Cette étude a montré que leur structure dépend de facteurs extérieurs. Il pourrait s'agir d'une autre région de la protéine et / ou de la membrane.Dans une troisième partie, un test permettant de suivre la fusion de cellules transfectées a été mis au point. Ceci nous a permis de caractériser de façon fonctionnelle l'ensemble des mutants réalisés et de préciser le rôle de différents domaines de G dans la fusion membranaire qu'elle induit

Rabies virus glycoprotein can fold in two alternative, antigenically distinct conformations depending on membrane-anchor type

International audienceRabies virus glycoprotein (G) is a trimeric type I transmembrane glycoprotein that mediates both receptor recognition and low pH-induced membrane fusion. We have previously demonstrated that a soluble form of the ectodomain of G (G(1-439)), although secreted, is folded in an alternative conformation, which is monomeric and antigenically distinct from the native state of the complete, membrane-anchored glycoprotein. This has raised questions concerning the role of the transmembrane domain (TMD) in the correct native folding of the ectodomain. Here, we show that an ectodomain anchored in the membrane by a glycophosphatidylinositol is also folded in an alternative conformation, whereas replacement of the TMD of G by other peptide TMDs results in correct antigenicity of G. However, mutants with an insertion of a hydrophilic linker between the ectodomain and the TMD also fold in an alternative conformation. The influence of the membrane-anchor type on G ectodomain trimerization and folding is discussed

Exolysin Shapes the Virulence of Pseudomonas aeruginosa Clonal Outliers

Bacterial toxins are important weapons of toxicogenic pathogens. Depending on their origin, structure and targets, they show diverse mechanisms of action and effects on eukaryotic cells. Exolysin is a secreted 170 kDa pore-forming toxin employed by clonal outliers of Pseudomonas aeruginosa providing to some strains a hyper-virulent behaviour. This group of strains lacks the major virulence factor used by classical strains, the Type III secretion system. Here, we review the structural features of the toxin, the mechanism of its secretion and the effects of the pore formation on eukaryotic cells

Differential stability and fusion activity of Lyssavirus glycoprotein trimers

International audienceThe oligomeric structure and the fusion activity of lyssavirus glycoprotein (G) was studied by comparing G from Mokola virus (GMok) and rabies virus (PV strain) (GPV), which are highly divergent lyssaviruses. G expressed at the surface of BSR cells upon either plasmid transfection or virus infection are shown to be mainly trimeric after cross-linking experiments. However, solubilization by a detergent (CHAPS) and analysis in sucrose sedimentation gradient evidenced that GMok trimer is less stable than GPV trimer. A chimeric glycoprotein (G Mok-PV) associating the N-terminal half of GMok to the C-terminal half part of GPV formed trimers with an intermediate stability, indicating that the G C-terminal domain is essential in trimer stability. A cell to cell fusion assay revealed that GMok (and not G Mok-PV) was able to induce fusion at a higher pH (0.5 pH unit) than GPV. Such differences in the oligomeric structure stability and in the fusion activity of lyssavirus glycoproteins may partly account for the previously reported differences of their immunogenic and pathogenic properties