Rescuing stalled ribosomes often involves their splitting into subunits. In many bacteria, the resultant large subunits bearing peptidyl-tRNAs are processed by the ribosome-associated quality control ...(RQC) apparatus that extends the C termini of the incomplete nascent polypeptides with polyalanine tails to facilitate their degradation. Although the tailing mechanism is well established, it is unclear how the nascent polypeptides are cleaved off the tRNAs. We show that peptidyl-tRNA hydrolase (Pth), the known role of which has been to hydrolyze ribosome-free peptidyl-tRNA, acts in concert with RQC factors to release nascent polypeptides from large ribosomal subunits. Dislodging from the ribosomal catalytic center is required for peptidyl-tRNA hydrolysis by Pth. Nascent protein folding may prevent peptidyl-tRNA retraction and interfere with the peptide release. However, oligoalanine tailing makes the peptidyl-tRNA ester bond accessible for Pth-catalyzed hydrolysis. Therefore, the oligoalanine tail serves not only as a degron but also as a facilitator of Pth-catalyzed peptidyl-tRNA hydrolysis.
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•Peptidyl-tRNA stuck inside the bacterial large ribosomal subunit is released by Pth•Pth action requires the retraction of peptidyl-tRNA from the ribosomal catalytic center•Nascent polypeptide folding may prevent peptidyl-tRNA retraction and release by Pth•RQC machinery-mediated alanine tailing facilitates peptidyl-tRNA release by Pth
Svetlov et al. show that, following ribosome splitting, peptidyl-tRNA that remains stuck inside the large ribosomal subunit is released by peptidyl-tRNA hydrolase (Pth). This release requires the retraction of peptidyl-tRNA from the subunit to expose its ester bond to Pth. The release is promoted by the C-terminal oligoalanine tailing of the nascent polypeptide.
France has a moderate level of seismic activity, characterized by diffuse seismicity, sometimes experiencing earthquakes of a magnitude of more than 5 in the most active zones. In this seismicity ...context, Grenoble is a city of major economic and social importance. However, earthquakes being rare, public authorities and the decision makers are only vaguely committed to reducing seismic risk: return periods are long and local policy makers do not have much information available. Over the past 25 yr, a large number of studies have been conducted to improve our knowledge of seismic hazard in this region. One of the decision-making concerns of Grenoble's public authorities, as managers of a large number of public buildings, is to know not only the seismic-prone regions, the variability of seismic hazard due to site effects and the city's overall vulnerability, but also the level of seismic risk and exposure for the entire city, also compared to other natural or/and domestic hazards. Our seismic risk analysis uses a probabilistic approach for regional and local hazards and the vulnerability assessment of buildings. Its applicability to Grenoble offers the advantage of being based on knowledge acquired by previous projects conducted over the years. This paper aims to compare the level of seismic risk with that of other risks and to introduce the notion of risk acceptability in order to offer guidance in the management of seismic risk. This notion of acceptability, which is now part of seismic risk consideration for existing buildings in Switzerland, is relevant in moderately seismic-prone countries like France.
The authors report the first archaeological case of dog ectoparasitosis in Ancient Egypt. The study of a mummified young dog dated to the Roman period suggests a significant infestation by two blood ...sucking ectoparasites, respectively the brown dog tick Rhipicephalus sanguineus Latreille, 1806 (Acari: Ixodidae), the louse fly Hippobosca longipennis Fabricius, 1805 (Diptera: Hippoboscidae) as well as puparia of sarcosaprophagous flies (Diptera: Sarcophagidae and Calliphoridae), a potential source of myiasis. All of these species are known to be potential vectors of different pathogens which may be responsible for the premature death of the dog.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The tripodal ligand (α,α‘,α‘ ‘nitrilotri(6-methyl-2-pyridinecarboxylic acid)) (H3tpaa) forms a Gd(III) complex which has a relaxivity (r 1p = 13.3 mM-1 s-1 at 25 °C and at 60 MHz) remarkably higher ...than those of the currently clinically used contrast agents based on octacoordinate polyaminocarboxylate complexes (3.5−4.7 mM-1 s-1) and a reasonably good thermodynamic stability. The crystal structure of the ligand and of its La, Nd, Eu, Gd, Tb, Ho, Tm, Yb, and Lu complexes have been determined by X-ray crystallography. The neutral H3tpaa molecule adopts, in the solid state, a preorganized tripodal conformation in which the three H3tpaa arms are located on the same side of the molecule, ready to bind a metal ion in a heptadentate coordination mode. The structures of the Ln(III) complexes vary along the series for their nuclearity and number of water molecules coordinated to the metal, and a tetrameric structure is observed for the La3+ ion (9- and 10-coordinate metal centers), dimeric structures are formed from the Nd3+ ion through the Yb3+ ion (9-coordinate), and a monomeric structure results for Lu3+ (8-coordinate). The relaxivity studies presented here suggest that the high relaxivity of the Gd(tpaa) complex is mainly the consequence of a shorter bound water proton−Gd(III) distance associated with a probable water coordination equilibrium between tris(aqua) and bis(aqua) complexes, giving raise to a mean number of coordinated water molecules q > 2. Both effects are strongly related to the ligand flexibility, which allows for a large volume available for water binding. The observed rapid water exchange rate is probably due to the presence of a low-energy barrier between 10-, 9-, and 8- coordinate geometries. Although the low solubility of the Gd complex of tpaa prevents its practical application as an MRI contrast agent, the straightforward introduction of substituents on the pyridine rings allows us to envisage ligands with a higher water solubility, containing functional groups leading to macromolecular systems with very high relaxivity.
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IJS, KILJ, NUK, PNG, UL, UM
1H NMR line‐shape analysis and magnetisation‐transfer experiments at variable temperature and pressure have been used to elucidate the solution dynamics of both M and m isomers of three ...Eu(dota‐tetraamide)(H2O)3+ complexes. The direct 1H NMR observation of the bound water signal allows the water‐exchange rates on each isomer to be measured individually. They are definitely independent of the ligand for both M and m isomers (M: k$\rm{_{ex}^{298}}$=9.4±0.2×103 s−1 for Eu(dotam)(H2O)3+, 8.2±0.2×103 s−1 for Eu(dtma)(H2O)3+ and 11.2±1.4×103 s−1 for Eu(dotmam)(H2O)3+; m: k$\rm{_{ex}^{298}}$=474±130×103 s−1 for Eu(dotam)(H2O)3+, 357±92×103 s−1 for Eu(dtma)(H2O)3+), and proceed through a dissociative mechanism (M isomers: ΔV ‡=+4.9 cm3 mol−1 for Eu(dotam)(H2O)3+ and +6.9 cm3 mol−1 for Eu(dtma)(H2O)3+). The overall water exchange only depends on the M/m isomeric ratio. The m isomer, which exchanges more quickly, is favoured by α‐substitution of the ring nitrogen. Therefore the synthesis of DOTA‐like ligands, which predominantly form complexes in the m form, should be a sufficient condition to ensure faster water exchange on potential GdIII‐based contrast agents. Furthermore the activation parameters for the water‐exchange and isomerisation processes are both compatible with a nonhydrated complex as intermediate.
Individual water‐exchange rates are measured for both isomers of three Eu(dota‐tetraamide)(H2O)3+ complexes by 1H NMR spectroscopy. Contrary to the isomeric ratio, the water‐exchange rate seems to be independent of the ligand. For the example shown, ΔV ‡ = +6.9 cm3 mol−1.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
The first variable-temperature and variable-pressure stopped-flow spectrophotometric study of the sequential threading of α-cyclodextrin (α-CD) onto the guest dye Mordant Orange 10, S, is reported. ...Complementary 1H one-dimensional (1D) variable-temperature kinetic studies and two-dimensional (2D) rotating-frame nuclear Overhauser effect spectroscopy (ROESY) and EXSY NMR studies are also reported. In aqueous solution at 298.2 K, the first α-CD threads onto S to form a 1:1 complex S·α-CD* with a forward rate constant k 1,f = 15 200 ± 200 M-1 s-1 and dethreads with a reverse rate constant k 1,r = 4.4 ± 0.3 s-1. Subsequently, S·α-CD* isomerizes to S·α-CD (k 3,f = 0.158 ± 0.006 s-1, k 3,f = 0.148 ± 0.006 s-1). This process can be viewed as a thermodynamically controlled molecular shuttle. A second α-CD threads onto S·α-CD* to form a 1:2 complex, S·(α-CD)2*, with k 2,f = 98 ± 2 M-1 s-1 and k 2,r = 0.032 ± 0.002 s-1. A second α-CD also threads onto S·α-CD to form another 1:2 complex, S·(α-CD)2, characterized by k 4,f = 9640 ± 1800 M-1 s-1 and k 4,r = 61 ± 6 s-1. Direct interconvertion between S·(α-CD)2* and S·(α-CD)2 was not detected; instead, they interconvert by dethreading the second α-CD and through the isomerization equilibrium between S·α-CD* and S·α-CD. The reaction volumes, ΔV 0, were found to be negative for the first three equilibria and positive for the fourth equilibrium. For the first three forward and reverse reactions, the volumes of activation are substantially more negative, indicating a compression of the transition state in comparison with the ground states. These data were used in conjunction with ΔH ⧧, ΔH°, ΔS ⧧, and ΔS° data to deduce the dominant mechanistic threading processes, which appear to be largely controlled by changes in hydration and van der Waals interactions, and possibly by conformational changes in both S and α-CD. The structure of the four complexes were deduced from 1H 2D ROESY NMR studies.
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IJS, KILJ, NUK, PNG, UL, UM
Since echinocandins are recommended as first line therapy for invasive candidiasis, detection of resistance, mainly due to alteration in FKS protein, is of main interest. EUCAST AFST recommends ...testing both MIC of anidulafungin and micafungin, and breakpoints (BPs) have been proposed to detect echinocandin-resistant isolates. We analyzed MIC distribution for all three available echinocandins of 2,787 clinical yeast isolates corresponding to 5 common and 16 rare yeast species, using the standardized EUCAST method for anidulafungin and modified for caspofungin and micafungin (AM3-MIC). In our database, 64 isolates of common pathogenic species were resistant to anidulafungin, according to the EUCAST BP, and/or to caspofungin, using our previously published threshold (AM3-MIC ≥ 0.5 mg/L). Among these 64 isolates, 50 exhibited 21 different FKS mutations. We analyzed the capacity of caspofungin AM3-MIC and anidulafungin MIC determination in detecting isolates with FKS mutation. They were always identified using caspofungin AM3-MIC and the local threshold while some isolates were misclassified using anidulafungin MIC and EUCAST threshold. However, both methods misclassified four wild-type C. glabrata as resistant. Based on a large data set from a single center, the use of AM3-MIC testing for caspofungin looks promising in identifying non-wild-type C. albicans, C. tropicalis and P. kudiravzevii isolates, but additional multicenter comparison is mandatory to conclude on the possible superiority of AM3-MIC testing compared to the EUCAST method.
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