Subscribe: Science: Current Issue
http://www.sciencemag.org/rss/current.xml
Added By: Feedage Forager Feedage Grade C rated
Language: English
Tags:
biological  cancer  complex  design  designed  nlp  optical  peptide  phase  single  spin  structure  structures  tubulin  vasohibins 
Rate this Feed
Rate this feedRate this feedRate this feedRate this feedRate this feed
Rate this feed 1 starRate this feed 2 starRate this feed 3 starRate this feed 4 starRate this feed 5 star

Comments (0)

Feed Details and Statistics Feed Statistics
Preview: Science: Current Issue

Science current issue



Science RSS feed -- current issue



 



Tax plans and science

2017-12-14T10:25:02-08:00




News at a glance

2017-12-14T10:25:02-08:00







France nabs foreign climate science talent

2017-12-14T10:25:02-08:00




Ice-shrouded life sees daylight

2017-12-14T10:25:02-08:00










Sudan seeks a science revival

2017-12-14T10:25:02-08:00




Not so fast

2017-12-14T10:25:02-08:00




A matter of trust

2017-12-14T10:25:02-08:00




Breaking the deadlock on ivory

2017-12-14T10:25:02-08:00




Closing the tubulin detyrosination cycle

2017-12-14T10:25:02-08:00




How plants differ in toxin-sensitivity

2017-12-14T10:25:02-08:00







Speeding up crystallization

2017-12-14T10:25:02-08:00




Fotis Kafatos (1940-2017)

2017-12-14T10:25:02-08:00










Arthur C. Clarke at 100

2017-12-14T10:25:02-08:00




Speak out against tuition waiver taxes

2017-12-14T10:25:02-08:00




Retinoic acid's reproducible future

2017-12-14T10:25:02-08:00




Lessons learned from cetacean tragedies

2017-12-14T10:25:02-08:00




Why aging attenuates antiviral responses

2017-12-14T10:25:02-08:00




Bacteria go the distance in cancer

2017-12-14T10:25:02-08:00




Stable catalysts through steaming

2017-12-14T10:25:02-08:00




Fast phase change with no preconditions

2017-12-14T10:25:02-08:00




Tuning the scattering of light

2017-12-14T10:25:02-08:00







A CRISPR device to record time

2017-12-14T10:25:02-08:00




How to survive a mass extinction

2017-12-14T10:25:02-08:00




An extra sugar protects

2017-12-14T10:25:02-08:00







Wired for success

2017-12-14T10:25:02-08:00




A rationally designed DNA-based oscillator

2017-12-14T10:25:02-08:00




Large origami from a single strand

2017-12-14T10:25:02-08:00




Breaking the symmetry in a supersolid

2017-12-14T10:25:02-08:00




Phase transition of scattered light

2017-12-14T10:25:02-08:00




Dispersing small, bimetallic nanoparticles

2017-12-14T10:25:02-08:00




A little zinc makes the rings all link

2017-12-14T10:25:02-08:00




Tubulin carboxypeptidase identity revealed

2017-12-14T10:25:02-08:00




Macrocycles by design

2017-12-14T10:25:02-08:00




How to save the African elephant

2017-12-14T10:25:02-08:00







Status is not everything

2017-12-14T10:25:02-08:00




Too much alike to be receptive

2017-12-14T10:25:02-08:00




Mechano-induced mitochondrial fission

2017-12-14T10:25:02-08:00




Editing genomes without breaks

2017-12-14T10:25:02-08:00




It just takes one "like"

2017-12-14T10:25:02-08:00




Trehalose confers superpowers

2017-12-14T10:25:02-08:00




When intuition overrides reason

2017-12-14T10:25:02-08:00




Fiber-optic earthquake detection

2017-12-14T10:25:02-08:00




Anomalous spin correlations and excitonic instability of interacting 2D Weyl fermions

2017-12-14T10:25:02-08:00

The Coulomb interaction in systems of quasi-relativistic massless electrons has an unscreened long-range component at variance with conventional correlated metals. We used nuclear magnetic resonance (NMR) measurements to reveal unusual spin correlations of two-dimensional Weyl fermions in an organic material, causing a divergent increase of the Korringa ratio by a factor of 1000 upon cooling, in marked contrast to conventional metallic behavior. Combined with model calculations, we show that this divergence stems from an interaction-driven velocity renormalization that almost exclusively suppresses zero-momentum spin fluctuations. At low temperatures, the NMR relaxation rate shows an unexpected increase; numerical analyses show that this increase corresponds to internode excitonic fluctuations, a precursor to a transition from massless to massive quasiparticles.




Purcell effect for active tuning of light scattering from semiconductor optical antennas

2017-12-14T10:25:02-08:00

Subwavelength, high–refractive index semiconductor nanostructures support optical resonances that endow them with valuable antenna functions. Control over the intrinsic properties, including their complex refractive index, size, and geometry, has been used to manipulate fundamental light absorption, scattering, and emission processes in nanostructured optoelectronic devices. In this study, we harness the electric and magnetic resonances of such antennas to achieve a very strong dependence of the optical properties on the external environment. Specifically, we illustrate how the resonant scattering wavelength of single silicon nanowires is tunable across the entire visible spectrum by simply moving the height of the nanowires above a metallic mirror. We apply this concept by using a nanoelectromechanical platform to demonstrate active tuning.




Disorder-induced optical transition from spin Hall to random Rashba effect

2017-12-14T10:25:02-08:00

Disordered structures give rise to intriguing phenomena owing to the complex nature of their interaction with light. We report on photonic spin-symmetry breaking and unexpected spin-optical transport phenomena arising from subwavelength-scale disordered geometric phase structure. Weak disorder induces a photonic spin Hall effect, observed via quantum weak measurements, whereas strong disorder leads to spin-split modes in momentum space, a random optical Rashba effect. Study of the momentum space entropy reveals an optical transition upon reaching a critical point where the structure’s anisotropy axis vanishes. Incorporation of singular topology into the disordered structure demonstrates repulsive vortex interaction depending on the disorder strength. The photonic disordered geometric phase can serve as a platform for the study of different phenomena emerging from complex media involving spin-orbit coupling.




Monitoring and manipulating Higgs and Goldstone modes in a supersolid quantum gas

2017-12-14T10:25:02-08:00

Higgs and Goldstone modes are collective excitations of the amplitude and phase of an order parameter that is related to the breaking of a continuous symmetry. We directly studied these modes in a supersolid quantum gas created by coupling a Bose-Einstein condensate to two optical cavities, whose field amplitudes form the real and imaginary parts of a U(1)-symmetric order parameter. Monitoring the cavity fields in real time allowed us to observe the dynamics of the associated Higgs and Goldstone modes and revealed their amplitude and phase nature. We used a spectroscopic method to measure their frequencies, and we gave a tunable mass to the Goldstone mode by exploring the crossover between continuous and discrete symmetry. Our experiments link spectroscopic measurements to the theoretical concept of Higgs and Goldstone modes.




Activation of surface lattice oxygen in single-atom Pt/CeO2 for low-temperature CO oxidation

2017-12-14T10:25:02-08:00

To improve fuel efficiency, advanced combustion engines are being designed to minimize the amount of heat wasted in the exhaust. Hence, future generations of catalysts must perform at temperatures that are 100°C lower than current exhaust-treatment catalysts. Achieving low-temperature activity, while surviving the harsh conditions encountered at high engine loads, remains a formidable challenge. In this study, we demonstrate how atomically dispersed ionic platinum (Pt2+) on ceria (CeO2), which is already thermally stable, can be activated via steam treatment (at 750°C) to simultaneously achieve the goals of low-temperature carbon monoxide (CO) oxidation activity while providing outstanding hydrothermal stability. A new type of active site is created on CeO2 in the vicinity of Pt2+, which provides the improved reactivity. These active sites are stable up to 800°C in oxidizing environments.




Reducing the stochasticity of crystal nucleation to enable subnanosecond memory writing

2017-12-14T10:25:02-08:00

Operation speed is a key challenge in phase-change random-access memory (PCRAM) technology, especially for achieving subnanosecond high-speed cache memory. Commercialized PCRAM products are limited by the tens of nanoseconds writing speed, originating from the stochastic crystal nucleation during the crystallization of amorphous germanium antimony telluride (Ge2Sb2Te5). Here, we demonstrate an alloying strategy to speed up the crystallization kinetics. The scandium antimony telluride (Sc0.2Sb2Te3) compound that we designed allows a writing speed of only 700 picoseconds without preprogramming in a large conventional PCRAM device. This ultrafast crystallization stems from the reduced stochasticity of nucleation through geometrically matched and robust scandium telluride (ScTe) chemical bonds that stabilize crystal precursors in the amorphous state. Controlling nucleation through alloy design paves the way for the development of cache-type PCRAM technology to boost the working efficiency of computing systems.




Synthesis of ultrasmall, homogeneously alloyed, bimetallic nanoparticles on silica supports

2017-12-14T10:25:02-08:00

Supported nanoparticles containing more than one metal have a variety of applications in sensing, catalysis, and biomedicine. Common synthesis techniques for this type of material often result in large, unalloyed nanoparticles that lack the interactions between the two metals that give the particles their desired characteristics. We demonstrate a relatively simple, effective, generalizable method to produce highly dispersed, well-alloyed bimetallic nanoparticles. Ten permutations of noble and base metals (platinum, palladium, copper, nickel, and cobalt) were synthesized with average particle sizes from 0.9 to 1.4 nanometers, with tight size distributions. High-resolution imaging and x-ray analysis confirmed the homogeneity of alloying in these ultrasmall nanoparticles.




Eudicot plant-specific sphingolipids determine host selectivity of microbial NLP cytolysins

2017-12-14T10:25:02-08:00

Necrosis and ethylene-inducing peptide 1–like (NLP) proteins constitute a superfamily of proteins produced by plant pathogenic bacteria, fungi, and oomycetes. Many NLPs are cytotoxins that facilitate microbial infection of eudicot, but not of monocot plants. Here, we report glycosylinositol phosphorylceramide (GIPC) sphingolipids as NLP toxin receptors. Plant mutants with altered GIPC composition were more resistant to NLP toxins. Binding studies and x-ray crystallography showed that NLPs form complexes with terminal monomeric hexose moieties of GIPCs that result in conformational changes within the toxin. Insensitivity to NLP cytolysins of monocot plants may be explained by the length of the GIPC head group and the architecture of the NLP sugar-binding site. We unveil early steps in NLP cytolysin action that determine plant clade-specific toxin selectivity.




Poly[n]catenanes: Synthesis of molecular interlocked chains

2017-12-14T10:25:02-08:00

As the macromolecular version of mechanically interlocked molecules, mechanically interlocked polymers are promising candidates for the creation of sophisticated molecular machines and smart soft materials. Poly[n]catenanes, where the molecular chains consist solely of interlocked macrocycles, contain one of the highest concentrations of topological bonds. We report, herein, a synthetic approach toward this distinctive polymer architecture in high yield (~75%) via efficient ring closing of rationally designed metallosupramolecular polymers. Light-scattering, mass spectrometric, and nuclear magnetic resonance characterization of fractionated samples support assignment of the high–molar mass product (number-average molar mass ~21.4 kilograms per mole) to a mixture of linear poly[7–26]catenanes, branched poly[13–130]catenanes, and cyclic poly[4–7]catenanes. Increased hydrodynamic radius (in solution) and glass transition temperature (in bulk materials) were observed upon metallation with Zn2+.




Structural basis of membrane disruption and cellular toxicity by {alpha}-synuclein oligomers

2017-12-14T10:25:02-08:00

Oligomeric species populated during the aggregation process of α-synuclein have been linked to neuronal impairment in Parkinson’s disease and related neurodegenerative disorders. By using solution and solid-state nuclear magnetic resonance techniques in conjunction with other structural methods, we identified the fundamental characteristics that enable toxic α-synuclein oligomers to perturb biological membranes and disrupt cellular function; these include a highly lipophilic element that promotes strong membrane interactions and a structured region that inserts into lipid bilayers and disrupts their integrity. In support of these conclusions, mutations that target the region that promotes strong membrane interactions by α-synuclein oligomers suppressed their toxicity in neuroblastoma cells and primary cortical neurons.




Analysis of Fusobacterium persistence and antibiotic response in colorectal cancer

2017-12-14T10:25:02-08:00

Colorectal cancers comprise a complex mixture of malignant cells, nontransformed cells, and microorganisms. Fusobacterium nucleatum is among the most prevalent bacterial species in colorectal cancer tissues. Here we show that colonization of human colorectal cancers with Fusobacterium and its associated microbiome—including Bacteroides, Selenomonas, and Prevotella species—is maintained in distal metastases, demonstrating microbiome stability between paired primary and metastatic tumors. In situ hybridization analysis revealed that Fusobacterium is predominantly associated with cancer cells in the metastatic lesions. Mouse xenografts of human primary colorectal adenocarcinomas were found to retain viable Fusobacterium and its associated microbiome through successive passages. Treatment of mice bearing a colon cancer xenograft with the antibiotic metronidazole reduced Fusobacterium load, cancer cell proliferation, and overall tumor growth. These observations argue for further investigation of antimicrobial interventions as a potential treatment for patients with Fusobacterium-associated colorectal cancer.




Vasohibins/SVBP are tubulin carboxypeptidases (TCPs) that regulate neuron differentiation

2017-12-14T10:25:02-08:00

Reversible detyrosination of α-tubulin is crucial to microtubule dynamics and functions, and defects have been implicated in cancer, brain disorganization, and cardiomyopathies. The identity of the tubulin tyrosine carboxypeptidase (TCP) responsible for detyrosination has remained unclear. We used chemical proteomics with a potent irreversible inhibitor to show that the major brain TCP is a complex of vasohibin-1 (VASH1) with the small vasohibin binding protein (SVBP). VASH1 and its homolog VASH2, when complexed with SVBP, exhibited robust and specific Tyr/Phe carboxypeptidase activity on microtubules. Knockdown of vasohibins or SVBP and/or inhibitor addition in cultured neurons reduced detyrosinated α-tubulin levels and caused severe differentiation defects. Furthermore, knockdown of vasohibins disrupted neuronal migration in developing mouse neocortex. Thus, vasohibin/SVBP complexes represent long-sought TCP enzymes.




Vasohibins encode tubulin detyrosinating activity

2017-12-14T10:25:02-08:00

Tubulin is subjected to a number of posttranslational modifications to generate heterogeneous microtubules. The modifications include removal and ligation of the C-terminal tyrosine of -tubulin. The enzymes responsible for detyrosination, an activity first observed 40 years ago, have remained elusive. We applied a genetic screen in haploid human cells to find regulators of tubulin detyrosination. We identified SVBP, a peptide that regulates the abundance of vasohibins (VASH1 and VASH2). Vasohibins, but not SVBP alone, increased detyrosination of -tubulin, and purified vasohibins removed the C-terminal tyrosine of -tubulin. We found that vasohibins play a cell type–dependent role in detyrosination, although cells also contain an additional detyrosinating activity. Thus, vasohibins, hitherto studied as secreted angiogenesis regulators, constitute a long-sought missing link in the tubulin tyrosination cycle.




Multiplex recording of cellular events over time on CRISPR biological tape

2017-12-14T10:25:02-08:00

Although dynamics underlie many biological processes, our ability to robustly and accurately profile time-varying biological signals and regulatory programs remains limited. Here we describe a framework for storing temporal biological information directly in the genomes of a cell population. We developed a "biological tape recorder" in which biological signals trigger intracellular DNA production that is then recorded by the CRISPR-Cas adaptation system. This approach enables stable recording over multiple days and accurate reconstruction of temporal and lineage information by sequencing CRISPR arrays. We further demonstrate a multiplexing strategy to simultaneously record the temporal availability of three metabolites (copper, trehalose, and fucose) in the environment of a cell population over time. This work enables the temporal measurement of dynamic cellular states and environmental changes and suggests new applications for chronicling biological events on a large scale.




Comprehensive computational design of ordered peptide macrocycles

2017-12-14T10:25:02-08:00

Mixed-chirality peptide macrocycles such as cyclosporine are among the most potent therapeutics identified to date, but there is currently no way to systematically search the structural space spanned by such compounds. Natural proteins do not provide a useful guide: Peptide macrocycles lack regular secondary structures and hydrophobic cores, and can contain local structures not accessible with l-amino acids. Here, we enumerate the stable structures that can be adopted by macrocyclic peptides composed of l- and d-amino acids by near-exhaustive backbone sampling followed by sequence design and energy landscape calculations. We identify more than 200 designs predicted to fold into single stable structures, many times more than the number of currently available unbound peptide macrocycle structures. Nuclear magnetic resonance structures of 9 of 12 designed 7- to 10-residue macrocycles, and three 11- to 14-residue bicyclic designs, are close to the computational models. Our results provide a nearly complete coverage of the rich space of structures possible for short peptide macrocycles and vastly increase the available starting scaffolds for both rational drug design and library selection methods.




New Products

2017-12-14T10:25:02-08:00




My children help my science

2017-12-14T10:25:02-08:00




Enzyme-free nucleic acid dynamical systems

2017-12-14T10:25:02-08:00

Chemistries exhibiting complex dynamics—from inorganic oscillators to gene regulatory networks—have been long known but either cannot be reprogrammed at will or rely on the sophisticated enzyme chemistry underlying the central dogma. Can simpler molecular mechanisms, designed from scratch, exhibit the same range of behaviors? Abstract chemical reaction networks have been proposed as a programming language for complex dynamics, along with their systematic implementation using short synthetic DNA molecules. We developed this technology for dynamical systems by identifying critical design principles and codifying them into a compiler automating the design process. Using this approach, we built an oscillator containing only DNA components, establishing that Watson-Crick base-pairing interactions alone suffice for complex chemical dynamics and that autonomous molecular systems can be designed via molecular programming languages.




Single-stranded DNA and RNA origami

2017-12-14T10:25:02-08:00

Self-folding of an information-carrying polymer into a defined structure is foundational to biology and offers attractive potential as a synthetic strategy. Although multicomponent self-assembly has produced complex synthetic nanostructures, unimolecular folding has seen limited progress. We describe a framework to design and synthesize a single DNA or RNA strand to self-fold into a complex yet unknotted structure that approximates an arbitrary user-prescribed shape. We experimentally construct diverse multikilobase single-stranded structures, including a ~10,000-nucleotide (nt) DNA structure and a ~6000-nt RNA structure. We demonstrate facile replication of the strand in vitro and in living cells. The work here thus establishes unimolecular folding as a general strategy for constructing complex and replicable nucleic acid nanostructures, and expands the design space and material scalability for bottom-up nanotechnology.




The nanoscale circuitry of battery electrodes

2017-12-14T10:25:02-08:00

Developing high-performance, affordable, and durable batteries is one of the decisive technological tasks of our generation. Here, we review recent progress in understanding how to optimally arrange the various necessary phases to form the nanoscale structure of a battery electrode. The discussion begins with design principles for optimizing electrode kinetics based on the transport parameters and dimensionality of the phases involved. These principles are then used to review and classify various nanostructured architectures that have been synthesized. Connections are drawn to the necessary fabrication methods, and results from in operando experiments are highlighted that give insight into how electrodes evolve during battery cycling.