The influenza viruses cause annual epidemics of respiratory disease and occasional pandemics, which constitute a major public-health issue. The segmented negative-stranded RNAs are associated with the polymerase complex and nucleoprotein (NP), forming ribonucleoproteins (RNPs), which are responsible for virus transcription and replication. We describe the structure of native RNPs derived from virions. They show a double-helical conformation in which two NP strands of opposite polarity are associated with each other along the helix. Both strands are connected by a short loop at one end of the particle and interact with the polymerase complex at the other end. This structure will be relevant for unraveling the mechanisms of nuclear import of parental virus RNPs, their transcription and replication, and the encapsidation of progeny RNPs into virions.
The performance of MISTRAL is reported, the soft X-ray transmission microscopy beamline at the ALBA light source (Barcelona, Spain) which is primarily dedicated to cryo soft X-ray tomography (cryo-SXT) for three-dimensional visualization of whole unstained cells at spatial resolutions down to 30 nm (half pitch). Short acquisition times allowing for high-throughput and correlative microscopy studies have promoted cryo-SXT as an emerging cellular imaging tool for structural cell biologists bridging the gap between optical and electron microscopy. In addition, the beamline offers the possibility of imaging magnetic domains in thin magnetic films that are illustrated here with an example.
A group of proteins with cell membrane remodeling properties is also able to change dramatically the morphology of liposomes in vitro, frequently inducing tubulation. For a number of these proteins, the mechanism by which this effect is exerted has been proposed to be the embedding of amphipathic helices into the lipid bilayer. For proteins presenting BAR domains, removal of an N-terminal amphipathic alpha-helix (H0-NBAR) results in much lower membrane tubulation efficiency, pointing to a fundamental role of this protein segment. Here, we studied the interaction of a peptide corresponding to H0-NBAR with model lipid membranes. H0-NBAR bound avidly to anionic liposomes but partitioned weakly to zwitterionic bilayers, suggesting an essentially electrostatic interaction with the lipid bilayer. Interestingly, it is shown that after membrane incorporation, the peptide oligomerizes as an antiparallel dimer, suggesting a potential role of H0-NBAR in the mediation of BAR domain oligomerization. Through monitoring the effect of H0-NBAR on liposome shape by cryoelectron microscopy, it is clear that membrane morphology is not radically changed. We conclude that H0-NBAR alone is not able to induce vesicle curvature, and its function must be related to the promotion of the scaffold effect provided by the concave surface of the BAR domain.
BackgroundDifferent superparamagnetic iron oxide nanoparticles have been tested for their potential use in cancer treatment, as they enter into cells with high effectiveness, do not induce cytotoxicity, and are retained for relatively long periods of time inside the cells. We have analyzed the interaction, internalization and biocompatibility of dimercaptosuccinic acid-coated superparamagnetic iron oxide nanoparticles with an average diameter of 15 nm and negative surface charge in MCF-7 breast cancer cells.ResultsCells were incubated with dimercaptosuccinic acid-coated superparamagnetic iron oxide nanoparticles for different time intervals, ranging from 0.5 to 72 h. These nanoparticles showed efficient internalization and relatively slow clearance. Time-dependent uptake studies demonstrated the maximum accumulation of dimercaptosuccinic acid-coated superparamagnetic iron oxide nanoparticles after 24 h of incubation, and afterwards they were slowly removed from cells. Superparamagnetic iron oxide nanoparticles were internalized by energy dependent endocytosis and localized in endosomes. Transmission electron microscopy studies showed macropinocytosis uptake and clathrin-mediated internalization depending on the nanoparticles aggregate size. MCF-7 cells accumulated these nanoparticles without any significant effect on cell morphology, cytoskeleton organization, cell cycle distribution, reactive oxygen species generation and cell viability, showing a similar behavior to untreated control cells.ConclusionsAll these findings indicate that dimercaptosuccinic acid-coated superparamagnetic iron oxide nanoparticles have excellent properties in terms of efficiency and biocompatibility for application to target breast cancer cells.Electronic supplementary materialThe online version of this article (doi:10.1186/s12951-015-0073-9) contains supplementary material, which is available to authorized users.
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