Lipopolysaccharide is Inserted into the Outer Membrane through An Intramembrane Hole, A Lumen Gate, and the Lateral Opening of LptD

Lipopolysaccharide (LPS) is essential for the vitality of most Gram-negative bacteria and plays an important role in bacterial multidrug resistance. The LptD/E translocon inserts LPS into the outer leaflet, the mechanism of which is poorly understood. Here, we report mutagenesis, functional assays, and molecular dynamics simulations of the LptD/E complex, which suggest two distinct pathways for the insertion of LPS. The N-terminal domain of LptD comprises a hydrophobic slide that injects the acyl tails of LPS directly into the outer membrane through an intramembrane hole, while the core oligosaccharide and O-antigen pass a lumen gate that triggers the unzipping of the lateral opening between strands β1C and β26C of the barrel of LptD, to finalize LPS insertion. Mutation of the LPS transport related residues or block of the LPS transport pathways results in the deaths of Escherichia coli. These findings are important for the development of novel antibiotics

Structural basis of outer membrane protein insertion by the BAM complex

All Gram-negative bacteria, mitochondria and chloroplasts have outer membrane proteins (OMPs) that perform many fundamental biological processes. The OMPs in Gram-negative bacteria are inserted and folded into the outer membrane by the β-barrel assembly machinery (BAM). The mechanism involved is poorly understood, owing to the absence of a structure of the entire BAM complex. Here we report two crystal structures of the Escherichia coli BAM complex in two distinct states: an inward-open state and a lateral-open state. Our structures reveal that the five polypeptide transport-associated domains of BamA form a ring architecture with four associated lipoproteins, BamB–BamE, in the periplasm. Our structural, functional studies and molecular dynamics simulations indicate that these subunits rotate with respect to the integral membrane β-barrel of BamA to induce movement of the β-strands of the barrel and promote insertion of the nascent OMP

Cristallochimie des apatites biologiques et géologiques (marqueurs minéralogiques de la fossilisation)

Cette Thèse a pour but d étudier la cristallochimie des apatites, constituants majeurs des dents et des os des vertébrés, afin de discuter leur utilisation comme marqueurs de la fossilisation. Nous avons combiné des techniques expérimentales avancées (spectrométrie IR à basse température et RMN du solide) et des modélisations théoriques réalisées par des méthodes ab initio de type DFT. Le mécanisme de substitution des groupes carbonate aux groupes phosphate dans la "francolite" a pour la première fois été élucidé. L accord entre les résultats expérimentaux et leurs contreparties théoriques a permis de valider un modèle de substitution couplée où le carbonate occupe l'une des faces du site tétraédrique et le fluor le sommet opposé. Les propriétés spectrométriques spécifiques de ce défaut ont été déterminées et permettent son identification dans les échantillons naturels. D'autres modèles d'incorporation du carbonate ont également été étudiés et discutés à la lumière des résultats expérimentaux. Ces résultats ont ensuite été appliqués à l'étude de la transformation de fossiles de dents et d os. L'identification de l'environnement du carbonate de type "francolite" dans les échantillons d'émail de dents fossiles implique que celles-ci se transforment par dissolution-recristallisation. Cette observation est donc susceptible de remettre en cause l'utilisation des fossiles les plus transformés pour les reconstitutions paléo-environnementales. En comparaison, la fossilisation des os procède par un mécanisme plus complexe impliquant des réorganisations précoces de la structure phosphatée suivies à plus long terme par des remplacements par dissolution-recristallisationThis Thesis aims to study the crystal-chemistry of apatite, the main mineral constituent of vertebrate bones and teeth, in order to discuss its use as marker of fossilization. We have combined advanced experimental techniques (FTIR at low temperature and solid-state NMR MAS) and theoretical ab initio modelling carried out by DFT methods. The substitution mechanism of carbonate groups for phosphate groups in the sedimentary carbonate fluorapatite (francolite) has been for the first time elucidated. The agreement between experimental results and their theoretical counterparts allows validating a model of coupled substitution where carbonate occupies one face of the tetrahedral site and fluorine the opposite vertex. Specific spectroscopic properties of this defect have been determined and allow its identification in natural samples. Other models of carbonate incorporation have also been investigated and discussed under the light of experimental results. These results have been then applied to the study of the transformation of fossil teeth and bones. The identification of the "francolite-type carbonate defect in fossil tooth enamel implies that their transformation may occur through dissolution and recrystallization mechanisms. Our findings challenge the use of the most transformed fossils for paleoenvironmental reconstructions. In comparison, the fossil bones proceed by a complex mechanism involving early reorganization of the phosphate structure followed by longer-term replacements by dissolution-recrystallization mechanisms.PARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Parental Care in Reptiles

This open educational resource is a fun and engaging high school-level lecture including lecture notes on animal parental care highlighting reptile behaviors. We use survivorship curves to frame the lesson, having the class brainstorm on what animals fit in each survivorship curve, along with different species of reptiles that exhibit interesting parenting behaviors. At the end of the lecture, we highlight diverse scientists in the field to make the lecture more inclusive and welcoming

Construction of Highly Active Zn₃In₂S₆ (110)/g-C₃N₄ System by Low Temperature Solvothermal for Efficient Degradation of Tetracycline under Visible Light

Herein, Zn3In2S6 photocatalyst with (110) exposed facet was prepared by low temperature solvothermal method. On this basis, a highly efficient binary Zn3In2S6/g-C3N4 was obtained by low temperature solvothermal method and applied to the degradation of tetracycline (TC). The samples of the preparation were characterized by X-ray diffraction, scanning electron microscope, transmission electron microscope, UV–vis diffuse reflection spectroscopy, and photoluminescence spectroscopy. Furthermore, the degradation performance of photocatalysts on TC was investigated under different experimental conditions. Finally, the mechanism of Zn3In2S6/g-C3N4 composite material degrading TC is discussed. The results show that Zn3In2S6 and Zn3In2S6/g-C3N4 photocatalysts with excellent performance could be successfully prepared at lower temperature. The Zn3In2S6/g-C3N4 heterojunction photocatalyst could significantly improve the photocatalytic activity compared with g-C3N4. After 150 min of illumination, the efficiency of 80%Zn3In2S6/g-C3N4 to degrade TC was 1.35 times that of g-C3N4. The improvement of photocatalytic activity was due to the formation of Zn3In2S6/g-C3N4 heterojunction, which promoted the transfer of photogenerated electron–holes. The cycle experiment test confirmed that Zn3In2S6/g-C3N4 composite material had excellent stability. The free radical capture experiment showed that ·O2− was the primary active material. This study provides a new strategy for the preparation of photocatalysts with excellent performance at low temperature

Ubiquitous EEG Headset

BCI (brain-computer interface) is a technology for sending and receiving signals between the brain and external devices. EEG is a method of recording an electrical map of electrical activity on the scalp that has been shown to be representative of macroscopic activity beneath the surface layers of the brain. The availability and reliability of EEG signals make it the most commonly used method for brain-computer interfaces. In the current market, the signal acquisition of EEG equipment is generally composed of multiple electrodes, which is bulky and complex in design and cannot meet the portability. Therefore, this project’s goal is to design a portable EEG device that can be carried out and used easily. This paper presents the research and development process of an EEG portable device for the public to use to detect and improve users’ sleep with easy setup and guidance. It is designed to be a single-channel EEG device that can record neural activity in real time and transfer the data package to a smartphone through Bluetooth connections. The neural activity data can be later analyzed for users with the bundled apps

Infrared spectroscopic properties of goethite:anharmonic broadening, long-range electrostatic effects and Al substitution

The infrared spectrum and its temperature dependence (20-320 K) were collected on a synthetic goethite sample (alpha-FeOOH). In addition, the infrared powder absorption spectrum of goethite and aluminum-substituted goethite was computed using ab initio quantum mechanical calculations based on density functional theory. This combined experimental and theoretical approach allows (1) the unequivocal assignment of absorption bands to the corresponding vibrational modes, (2) separate identification of the effects of the particle shape and of the aluminum substitution on the infrared spectrum, and (3) a discussion of the anharmonic properties and the origin of the line broadening in goethite. In particular, the two well-resolved OH bending absorption bands show different temperature evolution. Their detailed analysis suggests that the broadening of the band at similar to 800 cm(-1) cannot be described solely by a usual three-phonon process. The strong anharmonic behavior of this mode implies the addition of a four-phonon process, such as a pure dephasing process. In our calculations, the effect of the Hubbard U correction is also investigated and found to be most visible on the OH stretching and bending modes, in relation to the associated structural relaxation. The OH stretching frequencies decrease, leading to a better agreement with experimental frequencies, while the OH bending frequencies increase