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Molecular tuning of CO2-to-ethylene conversion 期刊论文
NATURE, 2020, 577 (7791) : 509-+
作者:  Li, Fengwang;  39;Brien, Colin P.
收藏  |  浏览/下载：11/0  |  提交时间：2020/07/03

The electrocatalytic reduction of carbon dioxide, powered by renewable electricity, to produce valuable fuels and feedstocks provides a sustainable and carbon-neutral approach to the storage of energy produced by intermittent renewable sources(1). However, the highly selective generation of economically desirable products such as ethylene from the carbon dioxide reduction reaction (CO2RR) remains a challenge(2). Tuning the stabilities of intermediates to favour a desired reaction pathway can improve selectivity(3-5), and this has recently been explored for the reaction on copper by controlling morphology(6), grain boundaries(7), facets(8), oxidation state(9) and dopants(10). Unfortunately, the Faradaic efficiency for ethylene is still low in neutral media (60 per cent at a partial current density of 7 milliamperes per square centimetre in the best catalyst reported so far(9)), resulting in a low energy efficiency. Here we present a molecular tuning strategy-the functionalization of the surface of electrocatalysts with organic molecules-that stabilizes intermediates for more selective CO2RR to ethylene. Using electrochemical, operando/in situ spectroscopic and computational studies, we investigate the influence of a library of molecules, derived by electro-dimerization of arylpyridiniums(11), adsorbed on copper. We find that the adhered molecules improve the stabilization of an '  atop-bound'  CO intermediate (that is, an intermediate bound to a single copper atom), thereby favouring further reduction to ethylene. As a result of this strategy, we report the CO2RR to ethylene with a Faradaic efficiency of 72 per cent at a partial current density of 230 milliamperes per square centimetre in a liquid-electrolyte flow cell in a neutral medium. We report stable ethylene electrosynthesis for 190 hours in a system based on a membrane-electrode assembly that provides a full-cell energy efficiency of 20 per cent. We anticipate that this may be generalized to enable molecular strategies to complement heterogeneous catalysts by stabilizing intermediates through local molecular tuning.


Electrocatalytic reduction of CO2 over copper can be made highly selective by '  tuning'  the copper surface with adsorbed organic molecules to stabilize intermediates for carbon-based fuels such as ethylene


  
Structure of the human metapneumovirus polymerase phosphoprotein complex 期刊论文
NATURE, 2020, 577 (7789) : 275-+
作者:  Pan, Junhua;  Qian, Xinlei;  Lattmann, Simon;  El Sahili, Abbas;  Yeo, Tiong Han;  Jia, Huan;  Cressey, Tessa;  Ludeke, Barbara;  Noton, Sarah;  Kalocsay, Marian;  Fearns, Rachel;  Lescar, Julien
收藏  |  浏览/下载：12/0  |  提交时间：2020/07/03

Respiratory syncytial virus (RSV) and human metapneumovirus (HMPV) cause severe respiratory diseases in infants and elderly adults(1). No vaccine or effective antiviral therapy currently exists to control RSV or HMPV infections. During viral genome replication and transcription, the tetrameric phosphoprotein P serves as a crucial adaptor between the ribonucleoprotein template and the L protein, which has RNA-dependent RNA polymerase (RdRp), GDP polyribonucleotidyltransferase and cap-specific methyltransferase activities(2,3). How P interacts with L and mediates the association with the free form of N and with the ribonucleoprotein is not clear for HMPV or other major human pathogens, including the viruses that cause measles, Ebola and rabies. Here we report a cryo-electron microscopy reconstruction that shows the ring-shaped structure of the polymerase and capping domains of HMPV-L bound to a tetramer of P. The connector and methyltransferase domains of L are mobile with respect to the core. The putative priming loop that is important for the initiation of RNA synthesis is fully retracted, which leaves space in the active-site cavity for RNA elongation. P interacts extensively with the N-terminal region of L, burying more than 4,016 angstrom(2) of the molecular surface area in the interface. Two of the four helices that form the coiled-coil tetramerization domain of P, and long C-terminal extensions projecting from these two helices, wrap around the L protein in a manner similar to tentacles. The structural versatility of the four P protomers-which are largely disordered in their free state-demonstrates an example of a '  folding-upon-partner-binding'  mechanism for carrying out P adaptor functions. The structure shows that P has the potential to modulate multiple functions of L and these results should accelerate the design of specific antiviral drugs.


  
Internal state dynamics shape brainwide activity and foraging behaviour 期刊论文
NATURE, 2020, 577 (7789) : 239-+
作者:  Marques, Joao C.;  Li, Meng;  Schaak, Diane;  Robson, Drew N.;  Li, Jennifer M.
收藏  |  浏览/下载：5/0  |  提交时间：2020/07/03

The brain has persistent internal states that can modulate every aspect of an animal'  s mental experience(1-4). In complex tasks such as foraging, the internal state is dynamic(5-8). Caenorhabditis elegans alternate between local search and global dispersal(5). Rodents and primates exhibit trade-offs between exploitation and exploration(6,7). However, fundamental questions remain about how persistent states are maintained in the brain, which upstream networks drive state transitions and how state-encoding neurons exert neuromodulatory effects on sensory perception and decision-making to govern appropriate behaviour. Here, using tracking microscopy to monitor whole-brain neuronal activity at cellular resolution in freely moving zebrafish larvae(9), we show that zebrafish spontaneously alternate between two persistent internal states during foraging for live prey (Paramecia). In the exploitation state, the animal inhibits locomotion and promotes hunting, generating small, localized trajectories. In the exploration state, the animal promotes locomotion and suppresses hunting, generating long-ranging trajectories that enhance spatial dispersion. We uncover a dorsal raphe subpopulation with persistent activity that robustly encodes the exploitation state. The exploitation-state-encoding neurons, together with a multimodal trigger network that is associated with state transitions, form a stochastically activated nonlinear dynamical system. The activity of this oscillatory network correlates with a global retuning of sensorimotor transformations during foraging that leads to marked changes in both the motivation to hunt for prey and the accuracy of motor sequences during hunting. This work reveals an important hidden variable that shapes the temporal structure of motivation and decision-making.


  
Injured adult neurons regress to an embryonic transcriptional growth state 期刊论文
NATURE, 2020, 581 (7806) : 77-+
作者:  Wang, Ruicong;  Li, Hongda;  Wu, Jianfeng;  Cai, Zhi-Yu;  Li, Baizhou;  Ni, Hengxiao;  Qiu, Xingfeng;  Chen, Hui;  Liu, Wei;  Yang, Zhang-Hua;  Liu, Min;  Hu, Jin;  Liang, Yaoji;  Lan, Ping;  Han, Jiahuai;  Mo, Wei
收藏  |  浏览/下载：22/0  |  提交时间：2020/07/03

Grafts of spinal-cord-derived neural progenitor cells (NPCs) enable the robust regeneration of corticospinal axons and restore forelimb function after spinal cord injury(1)  however, the molecular mechanisms that underlie this regeneration are unknown. Here we perform translational profiling specifically of corticospinal tract (CST) motor neurons in mice, to identify their '  regenerative transcriptome'  after spinal cord injury and NPC grafting. Notably, both injury alone and injury combined with NPC grafts elicit virtually identical early transcriptomic responses in host CST neurons. However, in mice with injury alone this regenerative transcriptome is downregulated after two weeks, whereas in NPC-grafted mice this transcriptome is sustained. The regenerative transcriptome represents a reversion to an embryonic transcriptional state of the CST neuron. The huntingtin gene (Htt) is a central hub in the regeneration transcriptome  deletion of Htt significantly attenuates regeneration, which shows that Htt has a key role in neural plasticity after injury.


In mouse models of central nervous system injury, Htt is shown to be a key component of the regulatory program associated with reversion of the neuronal transcriptome to a less-mature state.


  
Base-pair conformational switch modulates miR-34a targeting of Sirt1 mRNA 期刊论文
NATURE, 2020, 583 (7814) : 139-+
作者:  Muniz, Juan A.;  Barberena, Diego;  Lewis-Swan, Robert J.;  Young, Dylan J.;  Cline, Julia R. K.;  Rey, Ana Maria;  Thompson, James K.
收藏  |  浏览/下载：22/0  |  提交时间：2020/07/03

MicroRNAs (miRNAs) regulate the levels of translation of messenger RNAs (mRNAs). At present, the major parameter that can explain the selection of the target mRNA and the efficiency of translation repression is the base pairing between the '  seed'  region of the miRNA and its counterpart mRNA(1). Here we use R-1 rho relaxation-dispersion nuclear magnetic resonance(2) and molecular simulations(3) to reveal a dynamic switch-based on the rearrangement of a single base pair in the miRNA-mRNA duplex-that elongates a weak five-base-pair seed to a complete seven-base-pair seed. This switch also causes coaxial stacking of the seed and supplementary helix fitting into human Argonaute 2 protein (Ago2), reminiscent of an active state in prokaryotic Ago(4,5). Stabilizing this transient state leads to enhanced repression of the target mRNA in cells, revealing the importance of this miRNA-mRNA structure. Our observations tie together previous findings regarding the stepwise miRNA targeting process from an initial '  screening'  state to an '  active'  state, and unveil the role of the RNA duplex beyond the seed in Ago2.


Repression of a messenger RNA by a cognate microRNA depends not only on complementary base pairing, but also on the rearrangement of a single base pair, producing a conformation that fits better within the human Ago2 protein.


  
Non-volatile electric control of spin-charge conversion in a SrTiO3 Rashba system 期刊论文
NATURE, 2020, 580 (7804) : 483-+
作者:  Collombet, Samuel;  Ranisavljevic, Noemie;  Nagano, Takashi;  Varnai, Csilla;  Shisode, Tarak;  Leung, Wing;  Piolot, Tristan;  Galupa, Rafael;  Borensztein, Maud;  Servant, Nicolas;  Fraser, Peter;  Ancelin, Katia;  Heard, Edith
收藏  |  浏览/下载：14/0  |  提交时间：2020/07/03

The polarization direction of a ferroelectric-like state can be used to control the conversion of spin currents into charge currents at the surface of strontium titanate, a non-magnetic oxide.


After 50 years of development, the technology of today'  s electronics is approaching its physical limits, with feature sizes smaller than 10 nanometres. It is also becoming clear that the ever-increasing power consumption of information and communication systems(1) needs to be contained. These two factors require the introduction of non-traditional materials and state variables. As recently highlighted(2), the remanence associated with collective switching in ferroic systems is an appealing way to reduce power consumption. A promising approach is spintronics, which relies on ferromagnets to provide non-volatility and to generate and detect spin currents(3). However, magnetization reversal by spin transfer torques(4) is a power-consuming process. This is driving research on multiferroics to achieve low-power electric-field control of magnetization(5), but practical materials are scarce and magnetoelectric switching remains difficult to control. Here we demonstrate an alternative strategy to achieve low-power spin detection, in a non-magnetic system. We harness the electric-field-induced ferroelectric-like state of strontium titanate (SrTiO3)(6-9) to manipulate the spin-orbit properties(10) of a two-dimensional electron gas(11), and efficiently convert spin currents into positive or negative charge currents, depending on the polarization direction. This non-volatile effect opens the way to the electric-field control of spin currents and to ultralow-power spintronics, in which non-volatility would be provided by ferroelectricity rather than by ferromagnetism.


  
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：21/0  |  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.


  
Observations of grain-boundary phase transformations in an elemental metal 期刊论文
NATURE, 2020, 579 (7799) : 375-+
作者:  Valente, Luis;  Phillimore, Albert B.;  Melo, Martim;  Warren, Ben H.;  Clegg, Sonya M.;  Havenstein, Katja;  Tiedemann, Ralph;  Illera, Juan Carlos;  Thebaud, Christophe;  Aschenbach, Tina;  Etienne, Rampal S.
收藏  |  浏览/下载：16/0  |  提交时间：2020/07/03

Atomic-resolution observations combined with simulations show that grain boundaries within elemental copper undergo temperature-induced solid-state phase transformation to different structures  grain boundary phases can also coexist and are kinetically trapped structures.


The theory of grain boundary (the interface between crystallites, GB) structure has a long history(1) and the concept of GBs undergoing phase transformations was proposed 50 years ago(2,3). The underlying assumption was that multiple stable and metastable states exist for different GB orientations(4-6). The terminology '  complexion'  was recently proposed to distinguish between interfacial states that differ in any equilibrium thermodynamic property(7). Different types of complexion and transitions between complexions have been characterized, mostly in binary or multicomponent systems(8-19). Simulations have provided insight into the phase behaviour of interfaces and shown that GB transitions can occur in many material systems(20-24). However, the direct experimental observation and transformation kinetics of GBs in an elemental metal have remained elusive. Here we demonstrate atomic-scale GB phase coexistence and transformations at symmetric and asymmetric [111 over bar ] tilt GBs in elemental copper. Atomic-resolution imaging reveals the coexistence of two different structures at sigma 19b GBs (where sigma 19 is the density of coincident sites and b is a GB variant), in agreement with evolutionary GB structure search and clustering analysis(21,25,26). We also use finite-temperature molecular dynamics simulations to explore the coexistence and transformation kinetics of these GB phases. Our results demonstrate how GB phases can be kinetically trapped, enabling atomic-scale room-temperature observations. Our work paves the way for atomic-scale in situ studies of metallic GB phase transformations, which were previously detected only indirectly(9,15,27-29), through their influence on abnormal grain growth, non-Arrhenius-type diffusion or liquid metal embrittlement.


  
Strain-hardening and suppression of shear-banding in rejuvenated bulk metallic glass 期刊论文
NATURE, 2020, 578 (7796) : 559-+
作者:  Papai, Gabor;  Frechard, Alexandre;  Kolesnikova, Olga;  Crucifix, Corinne;  Schultz, Patrick;  Ben-Shem, Adam
收藏  |  浏览/下载：12/0  |  提交时间：2020/07/03

Strain-hardening (the increase of flow stress with plastic strain) is the most important phenomenon in the mechanical behaviour of engineering alloys because it ensures that flow is delocalized, enhances tensile ductility and inhibits catastrophic mechanical failure(1,2). Metallic glasses (MGs) lack the crystallinity of conventional engineering alloys, and some of their properties-such as higher yield stress and elastic strain limit(3)-are greatly improved relative to their crystalline counterparts. MGs can have high fracture toughness and have the highest known '  damage tolerance'  (defined as the product of yield stress and fracture toughness)(4) among all structural materials. However, the use of MGs in structural applications is largely limited by the fact that they show strain-softening instead of strain-hardening  this leads to extreme localization of plastic flow in shear bands, and is associated with early catastrophic failure in tension. Although rejuvenation of an MG (raising its energy to values that are typical of glass formation at a higher cooling rate) lowers its yield stress, which might enable strain-hardening(5), it is unclear whether sufficient rejuvenation can be achieved in bulk samples while retaining their glassy structure. Here we show that plastic deformation under triaxial compression at room temperature can rejuvenate bulk MG samples sufficiently to enable strain-hardening through a mechanism that has not been previously observed in the metallic state. This transformed behaviour suppresses shear-banding in bulk samples in normal uniaxial (tensile or compressive) tests, prevents catastrophic failure and leads to higher ultimate flow stress. The rejuvenated MGs are stable at room temperature and show exceptionally efficient strain-hardening, greatly increasing their potential use in structural applications.


Bulk metallic glasses can acquire the ability to strain-harden through a mechanical rejuvenation treatment at room temperature that retains their non-crystalline structure.


  
Structural basis of ligand recognition and self-activation of orphan GPR52 期刊论文
NATURE, 2020
作者:  Liu, Guoxia;  Papa, Arianne;  Katchman, Alexander N.;  Zakharov, Sergey I.;  Roybal, Daniel;  Hennessey, Jessica A.;  Kushner, Jared;  Yang, Lin;  Chen, Bi-Xing;  Kushnir, Alexander;  Dangas, Katerina;  Gygi, Steven P.;  Pitt, Geoffrey S.;  Colecraft, Henry M.;  Ben-Johny, Manu;  Kalocsay, Marian;  Marx, Steven O.
收藏  |  浏览/下载：10/0  |  提交时间：2020/07/03

Structures of the orphan G-protein-coupled receptor GPR52 in ligand-free, G-protein-coupled and ligand-bound states reveal that extracellular loop 2 occupies the orthosteric binding pocket and functions as a built-in agonist to activate the receptor.


GPR52 is a class-A orphan G-protein-coupled receptor that is highly expressed in the brain and represents a promising therapeutic target for the treatment of Huntington'  s disease and several psychiatric disorders(1,2). Pathological malfunction of GPR52 signalling occurs primarily through the heterotrimeric G(s) protein(2), but it is unclear how GPR52 and G(s) couple for signal transduction and whether a native ligand or other activating input is required. Here we present the high-resolution structures of human GPR52 in three states: a ligand-free state, a G(s)-coupled self-activation state and a potential allosteric ligand-bound state. Together, our structures reveal that extracellular loop 2 occupies the orthosteric binding pocket and operates as a built-in agonist, conferring an intrinsically high level of basal activity to GPR52(3). A fully active state is achieved when G(s) is coupled to GPR52 in the absence of an external agonist. The receptor also features a side pocket for ligand binding. These insights into the structure and function of GPR52 could improve our understanding of other self-activated GPCRs, enable the identification of endogenous and tool ligands, and guide drug discovery efforts that target GPR52.