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Team Publications Molecular Microscopy of Membranes Year of publication 2014 Lin Jia, Di Cui, Jérôme Bignon, Aurelie Di Cicco, Joanna Wdzieczak-Bakala, Jianmiao Liu, Min-Hui Li (2014 May 19) Reduction-responsive cholesterol-based block copolymer vesicles for drug delivery. Biomacromolecules : 2206-17 : DOI : 10.1021/bm5003569 Summary We developed a new robust reduction-responsive polymersome based on the amphiphilic block copolymer PEG-SS-PAChol. The stability and robustness were achieved by the smectic physical cross-linking of cholesterol-containing liquid crystal polymer PAChol in the hydrophobic layer. The reduction-sensitivity was introduced by the disulfide bridge (-S-S-) that links the hydrophilic PEG block and the hydrophobic PAChol block. We used a versatile synthetic strategy based on atom transfer radical polymerization (ATRP) to synthesize the reduction-responsive amphiphilic block copolymers. The reductive cleavage of the disulfide bridge in the block copolymers was first evidenced in organic solution. The partial destruction of PEG-SS-PAChol polymersomes in the presence of a reducing agent was then demonstrated by cryo-electron microscopy. Finally, the calcein release from PEG-SS-PAChol polymersomes triggered by glutathione (GSH) was observed both in PBS suspension and in vitro inside the macrophage cells. High GSH concentrations (≥35 mM in PBS or artificially enhanced in macrophage cells by GSH-OEt pretreatment) and long incubation time (in the order of hours) were, however, necessary to get significant calcein release. These polymersomes could be used as drug carriers with very long circulation profiles and slow release kinetics. Ayako Yamada, Alexandre Mamane, Jonathan Lee-Tin-Wah, Aurélie Di Cicco, Coline Prévost, Daniel Lévy, Jean-François Joanny, Evelyne Coudrier, Patricia Bassereau (2014 Apr 7) Catch-bond behaviour facilitates membrane tubulation by non-processive myosin 1b. Nature communications : 3624 : DOI : 10.1038/ncomms4624 Summary Myosin 1b is a single-headed membrane-associated motor actin filaments to That Bind with a catch-hop behavior in response to load. In vivo, myosin 1b is required to form membrane tubules at Both endosomes and the trans-Golgi network. To suit les the link entre thesis Fundamental two properties, here we Investigate the capacity of myosin 1b to extract membrane tubes along bundled actin filaments in a minimum reconstituted system. We that show single-headed non-processive myosin 1b can extract membrane tubes at biologically relevant low density. In contrast to kinesins we do not observe motor accumulation at the tip, Suggesting que la Underlying mechanism for tube formation is different. In our theoretical model, myosin 1b catch-bond properties Facilitate tube extraction under the conditions of membrane voltage by Increasing Reducing the density of myo1b required to INSTITUT CURIE, 20 rue d’Ulm, 75248 Paris Cedex 05, France | 1 Team Publications Molecular Microscopy of Membranes pull tubes. Year of publication 2013 Bibiana Peralta, David Gil-Carton, Daniel Castaño-Díez, Aurelie Bertin, Claire Boulogne, Hanna M Oksanen, Dennis H Bamford, Nicola G A Abrescia (2013 Oct 3) Mechanism of membranous tunnelling nanotube formation in viral genome delivery. PLoS biology : e1001667 : DOI : 10.1371/journal.pbio.1001667 Summary In internal membrane-containing viruses, a lipid vesicle enclosed by the icosahedral capsid protects the genome. It has been postulated that this internal membrane is the genome delivery device of the virus. Viruses built with this architectural principle infect hosts in all three domains of cellular life. Here, using a combination of electron microscopy techniques, we investigate bacteriophage PRD1, the best understood model for such viruses, to unveil the mechanism behind the genome translocation across the cell envelope. To deliver its double-stranded DNA, the icosahedral protein-rich virus membrane transforms into a tubular structure protruding from one of the 12 vertices of the capsid. We suggest that this viral nanotube exits from the same vertex used for DNA packaging, which is biochemically distinct from the other 11. The tube crosses the capsid through an aperture corresponding to the loss of the peripentonal P3 major capsid protein trimers, penton protein P31 and membrane protein P16. The remodeling of the internal viral membrane is nucleated by changes in osmolarity and loss of capsid-membrane interactions as consequence of the de-capping of the vertices. This engages the polymerization of the tail tube, which is structured by membrane-associated proteins. We have observed that the proteo-lipidic tube in vivo can pierce the gram-negative bacterial cell envelope allowing the viral genome to be shuttled to the host cell. The internal diameter of the tube allows one double-stranded DNA chain to be translocated. We conclude that the assembly principles of the viral tunneling nanotube take advantage of proteo-lipid interactions that confer to the tail tube elastic, mechanical and functional properties employed also in other protein-membrane systems. Pierre Frederic Fribourg, Mohamed Chami, Carlos Oscar S Sorzano, Francesca Gubellini, Roberto Marabini, Sergio Marco, Jean-Michel Jault, Daniel Lévy (2013 Aug 7) 3D cryo-electron reconstruction of BmrA, a bacterial multidrug ABC transporter in an inward-facing conformation and in a lipidic environment. Journal of molecular biology : 2059-69 : DOI : 10.1016/j.jmb.2014.03.002 Summary ABC (ATP-binding cassette) membrane exporters are efflux transporters of a wide diversity of molecule across the membrane at the expense of ATP. A key issue regarding their catalytic cycle is whether or not their nucleotide-binding domains (NBDs) are physically disengaged in INSTITUT CURIE, 20 rue d’Ulm, 75248 Paris Cedex 05, France | 2 Team Publications Molecular Microscopy of Membranes the resting state. To settle this controversy, we obtained structural data on BmrA, a bacterial multidrug homodimeric ABC transporter, in a membrane-embedded state. BmrA in the apostate was reconstituted in lipid bilayers forming a mixture of ring-shaped structures of 24 or 39 homodimers. Three-dimensional models of the ring-shaped structures of 24 or 39 homodimers were calculated at 2.3 nm and 2.5 nm resolution from cryo-electron microscopy, respectively. In these structures, BmrA adopts an inward-facing open conformation similar to that found in mouse P-glycoprotein structure with the NBDs separated by 3 nm. Both lipidic leaflets delimiting the transmembrane domains of BmrA were clearly resolved. In planar membrane sheets, the NBDs were even more separated. BmrA in an ATP-bound conformation was determined from two-dimensional crystals grown in the presence of ATP and vanadate. A projection map calculated at 1.6 nm resolution shows an open outwardfacing conformation. Overall, the data are consistent with a mechanism of drug transport involving large conformational changes of BmrA and show that a bacterial ABC exporter can adopt at least two open inward conformations in lipid membrane. INSTITUT CURIE, 20 rue d’Ulm, 75248 Paris Cedex 05, France | 3