An elusive goal for systemic drug delivery is to provide both spatial and temporal control of drug release. Liposomes have been evaluated as drug delivery vehicles for decades 1-5 , but their clinical significance has been limited by slow release or poor availability of the encapsulated drug 6 . Here we show that near-complete liposomal release can be initiated within seconds by irradiating hollow gold nanoshells (HGNs) with a near-infrared (NIR) pulsed laser. Our findings reveal that different coupling methods, such as having the HGNs tethered to, encapsulated within, or suspended freely outside the liposomes, all triggered liposomal release but with different levels of efficiency. For the underlying content release mechanism, our experiments suggest that microbubble formation and collapse due to the rapid temperature increase of the HGN is responsible for liposome disruption, as evidenced by the formation of solid gold particles after NIR irradiation and the coincidence of a laser power threshold for both triggered release and pressure fluctuations in the solution associating with cavitations. These effects are similar to those induced by ultrasound and our approach is conceptually analogous to use optically triggered nano-"sonicators" deep inside the body for drug delivery. We expect HGNs can be coupled with any nanocarriers to promote spatially and temporally controlled drug release. In addition, the capability of external HGNs to permeabilize lipid membranes can facilitate the cellular uptake of macromolecules, including proteins and DNA and allow for promising applications in gene therapy.One major challenge for current drug delivery is to control the drug release both spatially and temporally. Liposomes have been evaluated as drug delivery vehicles for decades 1-5 , but their clinical significance has been limited by slow release or poor availability of the encapsulated drug 6 . Here we show that near-complete liposomal release can be initiated within seconds ("burst" kinetics) by irradiating hollow gold nanoshells (HGNs) with a near-infrared (NIR) pulsed laser. Tissues are relatively transparent to NIR light which penetrates into body up to 10 cm 7 . This allows these HGN/liposome complexes to be addressed non-invasively within a significant fraction of the human body. Our findings on the underlying release mechanism reveal that this approach is conceptually analogous to using optically triggered nano-"sonicators" deep inside the body for drug delivery. Email: gorilla@engineering.ucsb Liposomes optimized to be highly stable and resistant to drug leakage in the circulation 8,9 are hampered by suboptimal drug release to serve as drug carriers. Current endogenous strategies in drug release have focused on incorporating components into liposomes to achieve either thermal, pH, enzymatically triggered or receptor-targeted liposomes 3-5 , however, none of them has led to marketed drugs 10 . It is difficult to include a destabilizing agent into the liposomes to promote release without compromising their ...

Group II chaperonins are essential mediators of cellular protein folding in eukaryotes and archaea. These oligomeric protein machines, ~1MDa, consist of two back-to-back rings encompassing a central cavity that accommodates polypeptide substrates1,2,3. Chaperonin-mediated protein folding is critically dependent on the closure of a built-in lid4,5, which is triggered by ATP hydrolysis6. The structural rearrangements and molecular events leading to lid closure are still unknown. Here, we report four single particle cryo-EM structures of Mm-cpn, an archaeal group II chaperonin5,7, in the nucleotide-free (open) and nucleotide-induced (closed) states. The 4.3 Å resolution of the closed conformation allowed building of the first ever atomic model directly from the cryo-EM density map, in which we were able to visualize the nucleotide and over 70% of the sidechains. The model of the open conformation was obtained by using the deformable elastic network modeling with the 8 Å resolution open state cryo-EM density restraints. Together, the open and closed structures reveal how local conformational changes triggered by ATP hydrolysis lead to an alteration of intersubunit contacts within and across the rings, ultimately causing a rocking motion that closes the ring. Our analysis reveals an intricate and unforeseen set of interactions controlling allosteric communication and inter-ring signaling driving the conformational cycle of group II chaperonins. Beyond this, we anticipate our methodology of combining single particle cryo-EM and computational modeling will become a powerful tool in the determination of atomic details involved in the dynamic processes of macromolecular machines in solution.

Podovirus P-SSP7 infects Prochlorococcus marinus, the most abundant oceanic photosynthetic microorganism. Single particle cryo-electron microscopy (cryo-EM) yields icosahedral and asymmetrical structures of infectious P-SSP7 with 4.6 Å and 9 Å resolution, respectively. The asymmetric reconstruction reveals how symmetry mismatches are accommodated among 5 of the gene products at the portal vertex. Reconstructions of infectious and empty particles show a conformational change of the “valve” density in the nozzle, an orientation difference in the tail fibers, a disordering of the C-terminus of the portal protein, and disappearance of the core proteins. In addition, cryo-electron tomography (cryo-ET) of P-SSP7 infecting Prochlorococcus demonstrated the same tail fiber conformation as in empty particles. Our observations suggest a mechanism whereby, upon binding to the host cell, the tail fibers induce a cascade of structural alterations of the portal vertex complex that triggers DNA release.

SummaryCyanobacteria are photosynthetic organisms responsible for ~25% of organic carbon fixation on earth. These bacteria began to convert solar energy and carbon dioxide into bioenergy and oxygen billions of years ago. Cyanophages, which infect these bacteria, play an important role in regulating the marine ecosystem by controlling cyanobacteria community organization and mediating lateral gene transfer. Here we visualize the maturation process of cyanophage Syn5 inside its host cell, Synechococcus, using Zernike Phase Contrast (ZPC) electron cryo-tomography (cryoET) 1,2 . This imaging modality yields significant enhancement of image contrast over conventional cryoET and thus facilitates the direct identification of subcellular components, including thylakoid membranes, carboxysomes and polyribosomes, as well as phages, inside the congested cytosol of the infected cell. By correlating the structural features and relative abundance of viral progeny within cells at different stages of infection, we identified distinct Syn5 assembly Users may view, print, copy, download and text and data-mine the content in such documents, for the purposes of academic research, subject always to the full Conditions of use: http://www.nature.com/authors/editorial_policies/license.html#terms The averaged density maps of the procapsid, expanded capsid and the DNA-containing capsid have been deposited in the EBI under accession codes EMD-5742, EMD-5743, EMD-5744, EMD-5745, and EMD-5746, respectively. The authors declare no competing financial interests.Supplementary Information is linked to the online version of the paper at www.nature.com/nature. Fig. 1a-b) are roughly concentric, the thylakoid membrane does not fully enclose the inner compartment of the cell, nor does it seem to directly interact with the cell membrane. This differs from the organization seen in other cyanobacteria 9,10 . Cyanobacteria also contain carboxysomes, polyhedral compartments encapsulating enzymes for carbon fixation 11,12 . Each WH8109 cell has, on average, four or five carboxysomes, with diameters ranging from 920 to 1160Å (Fig. 1c). Ribosomes are abundant and widespread, forming numerous intracellular patches that contain polyribosomes (Fig. 1d). HHS Public AccessCyanophage Syn5 that infects WH8109 cells is a short-tailed icosahedral phage with a unique horn appendage at the vertex opposite to the tail 13 (Extended Data Fig. 2). Initial segmentation of our tomograms of infected cells identified Syn5 particles on the cell surface, floating in the extracellular medium, and Syn5 progeny inside the cell. Multiple full and empty phage particles are seen attached to the cell surface. Injection of viral DNA occurs at multiple sites on the bacterial envelope and does not appear to be a coordinated process. Fig. 1e shows a tubular density extending from the phage tail through the periplasm to the cytoplasm (Supplementary video 4), similar to observations in other phage-infected bacteria 14,15 . As infection progresses, increasing numbers of Syn5 phage progeny ...

Trypanosoma brucei is a parasitic protozoan that causes African sleeping sickness. It contains a flagellum required for locomotion and viability. In addition to a microtubular axoneme, the flagellum contains a crystalline paraflagellar rod (PFR) and connecting proteins. We show here, by cryoelectron tomography, the structure of the flagellum in three bending states. The PFR lattice in straight flagella repeats every 56 nm along the length of the axoneme, matching the spacing of the connecting proteins. During flagellar bending, the PFR crystallographic unit cell lengths remain constant while the interaxial angles vary, similar to a jackscrew. The axoneme drives the expansion and compression of the PFR lattice. We propose that the PFR modifies the in-plane axoneme motion to produce the characteristic trypanosome bihelical motility as captured by high-speed light microscope videography.T rypanosoma brucei has devastated the African continent for centuries by infecting humans and domestic animals and has hindered economic development in sub-Saharan Africa (1). Current sleeping sickness treatments are inadequate and the drugs used are highly toxic (2). In recent years, the motility of the T. brucei flagellum has been found to be essential for parasite survival, infection, and disease pathogenesis (3), and has emerged as a promising drug target (4). Flagella with similar structural organization and protein composition have also been found in euglenoids (5) and other kinetoplastid parasites including Leishmania spp. and Trypanosoma cruzi, which cause Leishmaniasis and Chagas disease, respectively (6).The trypanosome flagellum is more complex than most other eukaryotic microtubule-based flagella (7-9) and is completely different from rotary-motor based bacterial flagella (10). Each T. brucei cell contains one flagellum that moves the cell body in an alternating right and left-handed twist resulting in bihelical motion (11) (Movie S1). The membrane-enclosed flagellum, composed of an axoneme, a paraflagellar rod (PFR) (12), and connecting proteins, is attached to the cell body (Fig. 1). PFR was identified as a lattice-like ultrastructure in T. brucei flagellum (13). This periodic and crystalline nature of the PFR was confirmed in T. brucei (14) and related species (15, 16). Monoclonal antibody screens (17) and proteomics studies (18-20) have identified at least 40 PFR proteins. Among them, PFR1 (73 kDa) and PFR2 (69 kDa), containing coiled-coil regions (21), are major structural components of the PFR (22). Depletion of these proteins results in failure of PFR assembly and cell motility defects (17, 23) ( Fig. S1 and Movie S2). In the T. brucei pathogenic bloodstream form, ablation of PFR2 causes death of the parasite (18). These results demonstrate a critical role of the PFR in T. brucei motility and viability. We have employed cryoelectron tomography (cryo-ET) to determine the structure of a biochemically isolated T. brucei flagella (18). We describe here a model that explains how the structure and arrangement of the fl...

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Bottom-up fabrication of self-assembled nanomaterials requires control over forces and interactions between building blocks. We here report on the formation and architecture of supramolecular structures constructed from two different peptide amphiphiles. Inclusion of four alanines between a 16-mer peptide and a 16-carbon long aliphatic tail resulted in a secondary structure shift of the peptide headgroups from alpha helices to beta sheets. A concomitant shift in self-assembled morphology from nano-ribbons to core-shell wormlike micelles was observed by cryogenic transmission electron microscopy (cryo-TEM) and atomic force microscopy (AFM). In presence of divalent magnesium ions, these a priori formed supramolecular structures interacted in distinct manners, highlighting the importance of peptide amphiphile design in self-assembly.

The aim of this study was to investigate the effect of dietary supplementation of nanosize zinc on zinc digestibility, growth performances, immune response and serum parameters of weanling piglets. Ninety-six LYD weanling piglets were assigned to control, zinc oxide (ZnO), organic-Zn (Zn-methionine) and nanosize ZnO (nano-Zn) groups with four replicates. The zinc was at the 120 mg/kg level in the treatment group's diet, while the control group's was 80 mg/kg Zn. The experiment results indicated that the nano-Zn and organic-Zn groups had significantly higher Zn digestibility compared to the ZnO and control groups. For the immune response traits, the IgG level and goat red blood cells (GRBC) antibody titer were nano-Zn and organic-Zn>ZnO>control; in the phytohemagglutinin (PHA) challenge test result, nano-Zn>organic-Zn>ZnO>control; in regard to the γ-globulin level, nano-Zn and organic-Zn>ZnO and control, with significant difference between groups. In the serum parameters aspect, serum Zn concentration in nano-Zn and organic-Zn groups were higher than in the ZnO and control groups, serum growth hormone concentration was increased in the nano-Zn group than in the other groups. In conclusion, nanosize zinc oxide for dietary supplementation can increase zinc digestibility, serum growth hormone levels and carbonic anhydrase activity and enhance the immune response of weanling piglets.