Bidimensional lamellar assembly by coordination of peptidic homopolymers to platinum nanoparticles

A key challenge for designing hybrid materials is the development of chemical tools to control the organization of inorganic nanoobjects at low scales, from mesoscopic (~µm) to nanometric (~nm). So far, the most efficient strategy to align assemblies of nanoparticles consists in a bottom-up approach by decorating block copolymer lamellae with nanoobjects. This well accomplished procedure is nonetheless limited by the thermodynamic constraints that govern copolymer assembly, the entropy of mixing as described by the Flory–Huggins solution theory supplemented by the critical influence of the volume fraction of the block components. Here we show that a completely different approach can lead to tunable 2D lamellar organization of nanoparticles with homopolymers only, on condition that few elementary rules are respected: 1) the polymer spontaneously allows a structural preorganization, 2) the polymer owns functional groups that interact with the nanoparticle surface, 3) the nanoparticles show a surface accessible for coordination

Observation of an anisotropic texture inside the wax layer of insect cuticle

International audienceThe outermost part of insect cuticles is very often covered with wax, which prevents desiccation and serves for chemical communication in many species. Earlier studies on cuticular waxes have mainly focused on their chemical composition revealing complex mixtures of lipids. In the absence of information on their physical organization, cuticular waxes have been considered isotropic. Here we report the presence of parallel stripes in the wax layer of the carapace of the scarab beetle, Chrysina gloriosa, with a textural periodicity of ca. 28 nm, as revealed by electron microscopy of transverse sections. Observations at oblique incidence argue for a layered organization of the wax, which might be related to a layer-by-layer deposition of excreted wax. Our findings may lay the foundation for further studies on the internal structure of cuticular waxes for other insects

Birc1e/Naip5 rapidly antagonizes modulation of phagosome maturation by Legionella pneumophila.

Legionella survives intracellularly by preventing fusion with lysosomes, due to phagosome escape from the endocytic pathway at an early stage of phagosome maturation, and by creating a replicative organelle that acquires endoplasmic reticulum (ER) characteristics through sustained interactions and fusion with the ER. Intracellular replication of Legionella pneumophila in mouse macrophages is controlled by the Lgn1 locus. Functional complementation in vivo has identified the Birc1e/Naip5 gene as being responsible for the Lgn1 effect. To understand the function and temporal site of action of Birc1e/Naip5 in susceptibility to L. pneumophila, we examined the biogenesis of Legionella-containing vacuoles (LCVs) formed in permissive A/J macrophages and in their Birc1e/Naip5 transgenic non-permissive counterpart. Birc1e/Naip5 effects on acquisition of lysosomal and ER markers were evident within 1-2 h following infection. A significantly higher proportion of LCVs formed in Birc1e/Naip5 transgenic macrophages had acquired the lysosomal markers cathepsin D and Lamp1 by 2 h post infection, whereas a significantly higher proportion of LCVs formed in permissive macrophages were positively stained for the ER markers BAP31 and calnexin, 6 h post infection. Likewise, studies by electron microscopy showed acquisition of lysosomal contents (horseradish peroxidase), within the first hour following phagocytic uptake, by LCVs formed in Birc1e/Naip5 transgenic macrophages and delivery of the ER marker glucose 6-phosphatase (G6Pase) only to the lumen of LCVs formed in A/J macrophages. Finally, a larger proportion of LCVs formed in A/J macrophages were studded with ribosomes 24 h post infection, compared with LCVs formed in Birc1e/Naip5 transgenic macrophages. These results suggest that sensing of L. pneumophila products by Birc1e/Naip5 in macrophages occurs rapidly following phagocytosis, a process that antagonizes the ability of L. pneumophila to remodel its phagosome into a specialized vacuole with ER characteristics

Separation of unsaturated C18 fatty acids using perfluorinated-micellar electrokinetic chromatography: II) role of nano-structuration

International audienceThree fatty acids were separated by micellar electrokinetic chromatography (MEKC) using ammonium perfluorooctanoate as volatile surfactant. Characterizations of both injection buffer and background electrolyte have been performed by complementary techniques including scattering experiments (light, x-rays) and NMR. Different structures have been observed such as small micelles at low methanol content and larger aggregates at high methanol content. In both cases fatty acids interact specifically with the perfluorinated self-assemblies due to different geometrical constraints and different interactions between polar head groups, ensuring separation by MEKC

Ligand Binding but Undetected Functional Response of FcR after Their Capture by T Cells via Trogocytosis

International audienceIntercellular transfer of cell surface proteins by trogocytosis is common and could affect T cell responses. Yet, the role of trogocytosis in T cell function is still elusive, and it is unknown whether a molecule, once captured by T cells, harbors the same biological properties as in donor APC. In this study, we showed that FcgammaR as well as the associated FcRgamma subunit could be detected at high levels on murine and human T cells after their intercellular transfer from FcgammaR-expressing APC. Capture of FcgammaR occurred during coculture of T cells with FcgammaR-expressing APC upon Ab- or Ag-mediated T cell stimulation. Once captured by T cells, FcgammaR were expressed in a conformation compatible with physiological function and conferred upon T cells the ability to bind immune complexes and to provision B cells with this source of Ag. However, we were unable to detect downstream signal or signaling-dependent function following the stimulation of FcgammaR captured by T cells, and biochemical studies suggested the improper integration of FcgammaR in the recipient T cell membrane. Thus, our study demonstrates that T cells capture FcgammaR that can efficiently exert ligand-binding activity, which, per se, could have functional consequences in T cell-B cell cooperation

Calcium carbonate precipitation by anoxygenic phototrophic bacteria.

16 pagesInternational audienceCarbonate biomineralization is considered as one of the main natural processes controlling CO2 levels in the atmosphere both in the past and at present time. In contrast to extensive studies of cyanobacterial calcification, biomineralization of anoxygenic phototrophic bacteria (APB) remained largely underestimated, despite their potentially important role on CaCO3 precipitation in the biomats, notably in the past. Haloalcaliphilic Rhodovulum steppense A-20s and halophilic neutrophilic Rhodovulum sp. S-17-65 were examined with respect to their ability to precipitate CaCO3 under controlled laboratory conditions. To characterize the link between the rate of bacterial growth (biomass production) and the rate of CaCO3 precipitation, batch kinetic experiments with live, dead and inactivated bacteria both in nutrient solution and in inert electrolyte were performed and produced precipitates were examined by SEM, TEM and XRD techniques. Active strains A-20s and S-17-65 precipitated calcite from initially supersaturated solutions (Ωcalcite = 10 to 40) via increasing Ωcalcite to 80–120 before the precipitation. The amount of precipitated CaCO3 (mole) was directly correlated with the amount of organic C in bacterial biomass produced with a slope of dependence ranging from 0.3 to 0.6 and from 0.1 to 0.3 for A-20s and S-17-65, respectively, depending on the initial solution composition. For both bacterial strains, only live actively photosynthetizing bacteria were capable of effectively decreasing Ca concentration and form CaCO3 with apparent bulk precipitation rates ranging from 0.001 to 0.0150 mmol/h at 10–20 gwet/L of biomass, similar to rates reported for other bacteria. SEM and XRD analyses of precipitates reveal the dominance of calcite with some amount of vaterite and monohydrocalcite forming spheres up to 100 μm diameter. The TEM analysis of bacterial suspension at the end of precipitation experiments did not demonstrate the presence of CaCO3 at the surface or in the vicinity of live cells. This suggests the existence of certain cell protection mechanism against carbonate precipitation at the cell surface. Given the lower efficiency of photoheterotrophic APB, compared to photoautotrophic cyanobacteria, to precipitate CaCO3 in natural conditions, it is possible that the overall potential of phototrophic community to form massive carbonate deposits was strongly limited before the appearance of oxygenic phototrophs

Experimental modeling of calcium carbonate precipitation by cyanobacterium Gloeocapsa sp.

17 pagesInternational audienceThe impact of cyanobacteria Gloeocapsa sp. on calcium carbonate precipitation has been examined by combining physico-chemical macroscopic and in-situ microscopic techniques. For this, Ca adsorption and assimilation and kinetic experiments were used to assess the existence of the metabolic process responsible for CaCO3 mineralization by Gloeocapsa sp. Experimental products were characterized by Scanning and Transmission Electron Microscopy (SEM and TEM) imaging, XRD analyses, coupled with Confocal Laser Scanning Microscopy (CLSM) and Raman micro-spectroscopy. Ca carbonate precipitation experiments were performed at an initial pH of 7.8 to 9.4 and 25 °C in supersaturated solutions (Ωcalcite = 1.5 to 150) in the presence of active cyanobacterial cells. During cyanobacterial photosynthesis, the solution pH increased up to 9.5-10.8 after the first 5-10 days of growth, the Ca concentration decreased and the supersaturation index attained a maximum followed by a gradual decrease due to progressive CaCO3 precipitation. Ca adsorption at the surface of live and inactivated Gloeocapsa sp. cells and Ca intracellular assimilation during cell growth were measured as a function of pH and Ca concentration in solution. The contribution of surface adsorption and intracellular uptake to total Ca removal from solution due to biocalcification does not exceed 10%. The presence of calcium carbonate, identified as calcite using Raman spectroscopy, on active Gloeocapsa sp. surfaces and in the vicinity of bacterial cell surfaces was evidenced using SEM. TEM and CLSM demonstrated cyanobacterial cell encrustation by CaCO3 precipitated in the form of nano-spheres adjacent to the cell surface. In contrast to other previously investigated calcifying bacteria, no cellular protection mechanism against Ca2 + adsorption and subsequent carbonate precipitation has been demonstrated for Gloeocapsa sp. This is most likely linked to the specific cellular organization of this species, which involves several cells in one single capsule. As such, planktonic cultures of Gloeocapsa sp. exhibit significant calcifying potential, making them important CO2-fixing microorganisms for both paleo-environmental reconstructions and technological applications

Good Vibrations: Structural Remodeling of Maturing Yeast Pre-40S Ribosomal Particles Followed by Cryo-Electron Microscopy

Assembly of eukaryotic ribosomal subunits is a very complex and sequential process that starts in the nucleolus and finishes in the cytoplasm with the formation of functional ribosomes. Over the past few years, characterization of the many molecular events underlying eukaryotic ribosome biogenesis has been drastically improved by the “resolution revolution” of cryo-electron microscopy (cryo-EM). However, if very early maturation events have been well characterized for both yeast ribosomal subunits, little is known regarding the final maturation steps occurring to the small (40S) ribosomal subunit. To try to bridge this gap, we have used proteomics together with cryo-EM and single particle analysis to characterize yeast pre-40S particles containing the ribosome biogenesis factor Tsr1. Our analyses lead us to refine the timing of the early pre-40S particle maturation steps. Furthermore, we suggest that after an early and structurally stable stage, the beak and platform domains of pre-40S particles enter a “vibrating” or “wriggling” stage, that might be involved in the final maturation of 18S rRNA as well as the fitting of late ribosomal proteins into their mature position

Inferring assembly-curving trends of bacterial micro-compartment shell hexamers from crystal structure arrangements

Bacterial microcompartments (BMC) are complex macromolecular assemblies that participate to varied chemical processes in about one fourth of bacterial species. BMC-encapsulated enzymatic activities are segregated from other cell contents by means of semipermeable shells, justifying why BMC are viewed as prototype nano-reactors for biotechnological applications. Herein, we undertook a comparative study of trends of self-assembly of BMC hexamers (BMC-H), the most abundant shell constituents. Published and new microscopy data show that some BMC-H, like -carboxysomal CcmK, tend to assemble flat whereas other BMC-H often build curved-implying objects. Inspection of available crystal structures presenting BMC-H in tiled arrangements permitted to identify two major assembly modes with a striking connection with experimental trends. All-atom molecular dynamics (MD) supported that BMC-H bending is triggered robustly only from the disposition adopted by BMC-H that form curved objects experimentally, conducting to almost identical arrangements to those found in structures of recomposed BMC shells. Simulations on ensembles of planar-behaving hexamers, which were previously reconfigured to comply with such disposition, confirmed that bending is defined by assembly details, rather than by BMC-H identity. Finally, although no common atomic determinants could be identified as responsible of BMC-H spontaneous curvature, an inter-hexamer ionic pair was pinpointed as contributor to hold a subset of BMC-H in low bending dispositions. These results are expected to improve our understanding of the variable mechanisms of biogenesis characterized for BMC, and of possible strategies to regulate BMC size and shape