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Transparent ferroelectric crystals with ultrahigh piezoelectricity 期刊论文
NATURE, 2020, 577 (7790) : 350-+
作者:  Qiu, Chaorui;  Wang, Bo;  Zhang, Nan;  Zhang, Shujun;  Liu, Jinfeng;  Walker, David;  Wang, Yu;  Tian, Hao;  Shrout, Thomas R.;  Xu, Zhuo;  Chen, Long-Qing;  Li, Fei
收藏  |  浏览/下载:47/0  |  提交时间:2020/07/03

Transparent piezoelectrics are highly desirable for numerous hybrid ultrasound-optical devices ranging from photoacoustic imaging transducers to transparent actuators for haptic applications(1-7). However, it is challenging to achieve high piezoelectricity and perfect transparency simultaneously because most high-performance piezoelectrics are ferroelectrics that contain high-density light-scattering domain walls. Here, through a combination of phase-field simulations and experiments, we demonstrate a relatively simple method of using an alternating-current electric field to engineer the domain structures of originally opaque rhombohedral Pb(Mg1/3Nb2/3)O-3-PbTiO3 (PMN-PT) crystals to simultaneously generate near-perfect transparency, an ultrahigh piezoelectric coefficient d(33) (greater than 2,100 picocoulombs per newton), an excellent electromechanical coupling factor k(33) (about 94 per cent) and a large electro-optical coefficient gamma(33) (approximately 220 picometres per volt), which is far beyond the performance of the commonly used transparent ferroelectric crystal LiNbO3. We find that increasing the domain size leads to a higher d(33) value for the [001]-oriented rhombohedral PMN-PT crystals, challenging the conventional wisdom that decreasing the domain size always results in higher piezoelectricity(8-10). This work presents a paradigm for achieving high transparency and piezoelectricity by ferroelectric domain engineering, and we expect the transparent ferroelectric crystals reported here to provide a route to a wide range of hybrid device applications, such as medical imaging, self-energy-harvesting touch screens and invisible robotic devices.


  
Structure of the ER membrane complex, a transmembrane-domain insertase 期刊论文
NATURE, 2020
作者:  Riemensberger, Johann;  Lukashchuk, Anton;  Karpov, Maxim;  Weng, Wenle;  Lucas, Erwan;  Liu, Junqiu;  Kippenberg, Tobias J.
收藏  |  浏览/下载:22/0  |  提交时间:2020/07/03

The cryo-electron microscopy structure of the ER membrane complex provides insight into its overall architecture, evolution and function in co-translational protein insertion.


The endoplasmic reticulum (ER) membrane complex (EMC) cooperates with the Sec61 translocon to co-translationally insert a transmembrane helix (TMH) of many multi-pass integral membrane proteins into the ER membrane, and it is also responsible for inserting the TMH of some tail-anchored proteins(1-3). How EMC accomplishes this feat has been unclear. Here we report the first, to our knowledge, cryo-electron microscopy structure of the eukaryotic EMC. We found that the Saccharomyces cerevisiae EMC contains eight subunits (Emc1-6, Emc7 and Emc10), has a large lumenal region and a smaller cytosolic region, and has a transmembrane region formed by Emc4, Emc5 and Emc6 plus the transmembrane domains of Emc1 and Emc3. We identified a five-TMH fold centred around Emc3 that resembles the prokaryotic YidC insertase and that delineates a largely hydrophilic client protein pocket. The transmembrane domain of Emc4 tilts away from the main transmembrane region of EMC and is partially mobile. Mutational studies demonstrated that the flexibility of Emc4 and the hydrophilicity of the client pocket are required for EMC function. The EMC structure reveals notable evolutionary conservation with the prokaryotic insertases(4,5), suggests that eukaryotic TMH insertion involves a similar mechanism, and provides a framework for detailed understanding of membrane insertion for numerous eukaryotic integral membrane proteins and tail-anchored proteins.


  
FACT caught in the act of manipulating the nucleosome 期刊论文
NATURE, 2020, 577 (7790) : 426-+
作者:  Shen, Helen
收藏  |  浏览/下载:15/0  |  提交时间:2020/07/03

The organization of genomic DNA into nucleosomes profoundly affects all DNA-related processes in eukaryotes. The histone chaperone known as '  facilitates chromatin transcription'  (FACT(1)) (consisting of subunits SPT16 and SSRP1) promotes both disassembly and reassembly of nucleosomes during gene transcription, DNA replication and DNA repair(2). However, the mechanism by which FACT causes these opposing outcomes is unknown. Here we report two cryo-electron-microscopic structures of human FACT in complex with partially assembled subnucleosomes, with supporting biochemical and hydrogen-deuterium exchange data. We find that FACT is engaged in extensive interactions with nucleosomal DNA and all histone variants. The large DNA-binding surface on FACT appears to be protected by the carboxy-terminal domains of both of its subunits, and this inhibition is released by interaction with H2A-H2B, allowing FACT-H2A-H2B to dock onto a complex containing DNA and histones H3 and H4 (ref. (3)). SPT16 binds nucleosomal DNA and tethers H2A-H2B through its carboxy-terminal domain by acting as a placeholder for DNA. SSRP1 also contributes to DNA binding, and can assume two conformations, depending on whether a second H2A-H2B dimer is present. Our data suggest a compelling mechanism for how FACT maintains chromatin integrity during polymerase passage, by facilitating removal of the H2A-H2B dimer, stabilizing intermediate subnucleosomal states and promoting nucleosome reassembly. Our findings reconcile discrepancies regarding the many roles of FACT and underscore the dynamic interactions between histone chaperones and nucleosomes.


  
Structures of human pannexin 1 reveal ion pathways and mechanism of gating 期刊论文
NATURE, 2020
作者:  Krause, David W.;  Hoffmann, Simone;  Hu, Yaoming;  Wible, John R.;  Rougier, Guillermo W.;  Kirk, E. Christopher;  Groenke, Joseph R.;  Rogers, Raymond R.;  Rossie, James B.;  Schultz, Julia A.;  Evans, Alistair R.;  von Koenigswald, Wighart;  Rahantarisoa, Lydia J.
收藏  |  浏览/下载:26/0  |  提交时间:2020/07/03

Cryo-electron microscopy structures of the ATP-permeable channel pannexin 1 reveal a gating mechanism involving multiple distinct ion-conducting pathways.


Pannexin 1 (PANX1) is an ATP-permeable channel with critical roles in a variety of physiological functions such as blood pressure regulation(1), apoptotic cell clearance(2) and human oocyte development(3). Here we present several structures of human PANX1 in a heptameric assembly at resolutions of up to 2.8 angstrom, including an apo state, a caspase-7-cleaved state and a carbenoxolone-bound state. We reveal a gating mechanism that involves two ion-conducting pathways. Under normal cellular conditions, the intracellular entry of the wide main pore is physically plugged by the C-terminal tail. Small anions are conducted through narrow tunnels in the intracellular domain. These tunnels connect to the main pore and are gated by a long linker between the N-terminal helix and the first transmembrane helix. During apoptosis, the C-terminal tail is cleaved by caspase, allowing the release of ATP through the main pore. We identified a carbenoxolone-binding site embraced by W74 in the extracellular entrance and a role for carbenoxolone as a channel blocker. We identified a gap-junction-like structure using a glycosylation-deficient mutant, N255A. Our studies provide a solid foundation for understanding the molecular mechanisms underlying the channel gating and inhibition of PANX1 and related large-pore channels.


  
Ball-and-chain inactivation in a calcium-gated potassium channel 期刊论文
NATURE, 2020, 580 (7802) : 288-+
作者:  Peron, Simon;  Pancholi, Ravi;  Voelcker, Bettina;  Wittenbach, Jason D.;  olafsdottir, H. Freyja;  Freeman, Jeremy;  Svoboda, Karel
收藏  |  浏览/下载:38/0  |  提交时间:2020/07/03

Cryo-electron microscopy structures and molecular dynamics simulations of the calcium-activated potassium channel MthK from Methanobacterium thermoautotrophicum are used to show that gating of this channel involves a ball-and-chain inactivation mechanism mediated by a previously unresolved N-terminal peptide.


Inactivation is the process by which ion channels terminate ion flux through their pores while the opening stimulus is still present(1). In neurons, inactivation of both sodium and potassium channels is crucial for the generation of action potentials and regulation of firing frequency(1,2). A cytoplasmic domain of either the channel or an accessory subunit is thought to plug the open pore to inactivate the channel via a '  ball-and-chain'  mechanism(3-7). Here we use cryo-electron microscopy to identify the molecular gating mechanism in calcium-activated potassium channels by obtaining structures of the MthK channel from Methanobacterium thermoautotrophicum-a purely calcium-gated and inactivating channel-in a lipid environment. In the absence of Ca2+, we obtained a single structure in a closed state, which was shown by atomistic simulations to be highly flexible in lipid bilayers at ambient temperature, with large rocking motions of the gating ring and bending of pore-lining helices. In Ca2+-bound conditions, we obtained several structures, including multiple open-inactivated conformations, further indication of a highly dynamic protein. These different channel conformations are distinguished by rocking of the gating rings with respect to the transmembrane region, indicating symmetry breakage across the channel. Furthermore, in all conformations displaying open channel pores, the N terminus of one subunit of the channel tetramer sticks into the pore and plugs it, with free energy simulations showing that this is a strong interaction. Deletion of this N terminus leads to functionally non-inactivating channels and structures of open states without a pore plug, indicating that this previously unresolved N-terminal peptide is responsible for a ball-and-chain inactivation mechanism.


  
Structural insight into arenavirus replication machinery 期刊论文
NATURE, 2020, 579 (7800) : 615-+
作者:  Zhang, Xiaheng;  Smith, Russell T.;  Le, Chip;  McCarver, Stefan J.;  Shireman, Brock T.;  Carruthers, Nicholas I.;  MacMillan, David W. C.
收藏  |  浏览/下载:40/0  |  提交时间:2020/07/03

The authors provide high-resolution structures of two arenavirus polymerases, revealing that the active site of arenavirus polymerase is inherently switched on, without the requirement for allosteric activation by 5 '  -viral RNA, and that dimerization facilitates polymerase activity.


Arenaviruses can cause severe haemorrhagic fever and neurological diseases in humans and other animals, exemplified by Lassa mammarenavirus, Machupo mammarenavirus and lymphocytic choriomeningitis virus, posing great threats to public health(1-4). These viruses encode a large multi-domain RNA-dependent RNA polymerase for transcription and replication of the viral genome(5). Viral polymerases are one of the leading antiviral therapeutic targets. However, the structure of arenavirus polymerase is not yet known. Here we report the near-atomic resolution structures of Lassa and Machupo virus polymerases in both apo and promoter-bound forms. These structures display a similar overall architecture to influenza virus and bunyavirus polymerases but possess unique local features, including an arenavirus-specific insertion domain that regulates the polymerase activity. Notably, the ordered active site of arenavirus polymerase is inherently switched on, without the requirement for allosteric activation by 5 '  -viral RNA, which is a necessity for both influenza virus and bunyavirus polymerases(6,7). Moreover, dimerization could facilitate the polymerase activity. These findings advance our understanding of the mechanism of arenavirus replication and provide an important basis for developing antiviral therapeutics.


  
Current-driven magnetic domain-wall logic 期刊论文
NATURE, 2020, 579 (7798) : 214-+
作者:  Culp, Elizabeth J.;  Waglechner, Nicholas;  Wang, Wenliang;  Fiebig-Comyn, Aline A.;  Hsu, Yen-Pang;  Koteva, Kalinka;  Sychantha, David;  Coombes, Brian K.;  Van Nieuwenhze, Michael S.;  Brun, Yves, V;  Wright, Gerard D.
收藏  |  浏览/下载:50/0  |  提交时间:2020/07/03

Spin-based logic architectures provide nonvolatile data retention, near-zero leakage, and scalability, extending the technology roadmap beyond complementary metal-oxide-semiconductor logic(1-13). Architectures based on magnetic domain walls take advantage of the fast motion, high density, non-volatility and flexible design of domain walls to process and store information(1,3,14-16). Such schemes, however, rely on domain-wall manipulation and clocking using an external magnetic field, which limits their implementation in dense, large-scale chips. Here we demonstrate a method for performing all-electric logic operations and cascading using domain-wall racetracks. We exploit the chiral coupling between neighbouring magnetic domains induced by the interfacial Dzyaloshinskii-Moriya interaction(17-20), which promotes non-collinear spin alignment, to realize a domain-wall inverter, the essential basic building block in all implementations of Boolean logic. We then fabricate reconfigurable NAND and NOR logic gates, and perform operations with current-induced domain-wall motion. Finally, we cascade several NAND gates to build XOR and full adder gates, demonstrating electrical control of magnetic data and device interconnection in logic circuits. Our work provides a viable platform for scalable all-electric magnetic logic, paving the way for memory-in-logic applications.


  
Towards seamless large-domain parameter estimation for hydrologic models 期刊论文
WATER RESOURCES RESEARCH, 2017, 53 (9)
作者:  Mizukami, Naoki;  Clark, Martyn P.;  Newman, Andrew J.;  Wood, Andrew W.;  Gutmann, Ethan D.;  Nijssen, Bart;  Rakovec, Oldrich;  Samaniego, Luis
收藏  |  浏览/下载:25/0  |  提交时间:2019/04/09
hydrologic modeling  parameter estimation  large domain