This Week in Science

Science  08 Aug 2014:
Vol. 345, Issue 6197, pp. 633
  1. Applied Origami

    Folding robots and metamaterials

    1. Marc S. Lavine

    Folded tessellated structures yield mechanical properties not found in nature

    CREDIT: JESSE L. SILVERBERG, ARTHUR A. EVANS, LAUREN MCLEOD, RYAN C. HAYWARD, THOMAS HULL, CHRIS D. SANTANGELO, AND ITAI COHEN

    The same principles used to make origami art can make self-assembling robots and tunable metamaterials—artificial materials engineered to have properties that may not be found in nature (see the Perspective by You). Felton et al. made complex self-folding robots from flat templates. Such robots could potentially be sent through a collapsed building or tunnels and then assemble themselves autonomously into their final functional form. Silverberg et al. created a mechanical metamaterial that was folded into a tessellated pattern of unit cells. These cells reversibly switched between soft and stiff states, causing large, controllable changes to the way the material responded to being squashed.

    Science, this issue p. 644, p. 647; see also p. 623

  2. Early Solar System

    Relocating a heavy-metal factory

    1. Margaret M. Moerchen

    We can learn about the solar system's past by measuring heavy radioactive isotopes in meteorites—the extraterrestrial equivalent of carbon dating on Earth. Elements heavier than iron are mainly synthesized in supernovae or asymptotic giant branch (AGB) stars. Knowing exactly which element is produced where, is key to dating the solar system. Lugaro et al. found that AGB stars generated more of a nuclide called 182Hf than previously thought (see the Perspective by Bizzarro). Its abundance indicates that it was produced about 30 million years before the Sun's formation.

    Science, this issue p. 650; see also p. 620

  3. Magnetic Microscopy

    Seeing magnetism on an atomic level

    1. Jelena Stajic

    Electrons tunneling from the magnetized tip of a scanning tunneling microscope into the surface of a material can reveal the material's magnetic structure. Although researchers have used the technique on simple nanostructures, they've had trouble preparing the tip in just the right way to visualize the magnetic order in more exotic materials. Enayat et al. used a tip with a magnetic cluster on its apex to reveal patterns of magnetic ordering in the material Fe1+yTe, which becomes superconducting by substituting Te with Se atoms. The researchers prepared the tip by simply picking up atoms from the surface of the material.

    Science, this issue p. 653

  4. Motor Neuron Disease

    Drugs that provide the splice of life

    1. Paula A. Kiberstis

    Motor neurons relay signals from the nervous system to muscle fibers. In patients with spinal muscular atrophy, a protein required for the survival of these neurons is deficient or missing altogether, so the neurons gradually die and the patients' muscles waste away. The disease is currently untreatable. Naryshkin et al. discovered small-molecule drugs that cause cells to produce the missing protein by altering how a specific mRNA is put together, or “spliced” (see the Perspective by Vigevani and Valcárcel). When the researchers used the drugs to treat diseased mice, the mice showed marked improvement in muscle mass, motor function, and survival.

    Science, this issue p. 688; see also p. 624

  5. Selective Attention

    You only see what you want to see

    1. Peter Stern

    We often focus on a particular item out of a thousand objects in a visual scene. This ability is called selective attention. Selective attention enhances the responses of sensory nerve cells to whatever is being observed and dampens responses to any distractions. Zhang et al. identified a region of the mouse forebrain that modulates responses in the visual cortex. This modulation improved the mouse's performance in a visual task.

    Science, this issue p. 660

  6. Artificial Brains

    Modeling computer chips on real brains

    1. Peter Stern

    Computers are nowhere near as versatile as our own brains. Merolla et al. applied our present knowledge of the structure and function of the brain to design a new computer chip that uses the same wiring rules and architecture. The flexible, scalable chip operated efficiently in real time, while using very little power.

    Science, this issue p. 668

  7. Oil Biodegradation

    Microbial life thrives in an oily bubble

    1. Nicholas S. Wigginton

    Microorganisms can break down hydrocarbons in oil reservoirs. Microbes grow primarily at the interface between oil and water, where they can find nutrients and dispose of metabolites. Meckenstock et al. now show that tiny water droplets can also provide a suitable home for hydrocarbon-degrading microorganisms. The authors examined oil from Pitch Lake, Trinidad and Tobago, and found that diverse microorganisms thrived in these tiny isolated microhabitats.

    Science, this issue p. 673

    Pitch Lake, Trinidad and Tobagao

    CREDIT: CHRISTINE UND DAVID SCHMITT/FLICKR
  8. Ribosome Structure

    Factors that aid ribosomal protein synthesis

    1. Valda Vinson

    The ribosome is a large macromolecular machine responsible for making proteins inside cells. During its mechanical cycle, parts of the ribosome must move. These movements are facilitated by proteins that bind to the ribosome. Gagnon et al. describe the structure of one such protein, Elongation Factor 4, bound to the ribosome. This protein appears to help the ribosome to reverse its conformation as it is making a protein, which might prevent the ribosome from stalling during protein synthesis.

    Science, this issue p. 684

  9. Cardiovascular Disease

    Better blood thinner, without bleeding

    1. Katrina. L. Kelner

    Blood thinners prevent heart attacks and strokes by making it harder for blood to clot, but these drugs can put patients at risk of dangerous bleeding. Now Moeckle et al. describe an enzyme that can prevent clots without this perilous side effect. They engineered the enzyme apyrase to remove the pro-clotting molecule ADP from the blood quickly. In dogs and mice with heart attacks, apyrase stopped blood cells from aggregating, the first step in forming a clot. At the highest dose, the animals suffered less heart damage and did not bleed excessively. In comparison, clopidogrel, a blood thinner used currently in patients, protected the heart less well and did cause excessive bleeding.

    Sci. Transl. Med., 6, 248ra105 (2014)

  10. Plant Development

    How to plumb the root is the problem

    1. Pamela J. Hines

    The vascular system of the plant root is generated from four seemingly similar cells. At some point, though, these cells' decendents need to follow different fates. Combining computational modeling with manipulation of hormone signaling in Arabidopsis, De Rybel et al. discovered the importance of a small bridge connecting two of the four cells (see the Perspective by Mellor and Bishopp). This feature locked in asymmetry in hormone signaling, so that those cells closest to the xylem delivered the maximal response. Two feedback loops in the model function distinctly, with one generating a domain rich in auxin and the other establishing a sharp boundary between domains.

    Science, this issue p. 636; see also p. 622

  11. Ammonia Synthesis

    Taking carbon out of the ammonial recipe

    1. Jake Yeston

    The reaction used to make ammonia for synthetic fertilizer requires hydrogen. Nowadays, that hydrogen is stripped from methane, creating CO2 as a by-product. Licht et al. demonstrate a relatively efficient electrochemical process in which water and nitrogen react directly to form ammonia. The approach removes the need for an independent hydrogen generation step. The process takes place in molten hydroxide salt and requires a nanostructured iron oxide–derived catalyst. Although the catalyst suspension is currently only stable for a few hours, the protocol points to a way to produce ammonia from purely renewable resources.

    Science, this issue p. 637

  12. Theoretical Chemistry

    Working out how to pack benzene in silico

    1. Jake Yeston

    Many organic compounds crystallize in several different energetically similar packing arrangements, or polymorphs. This complicates processes such as drug formulation that rely on reproducible crystallization. Yang et al. have now achieved the long-standing goal of calculating a crystal packing arrangement from first principles to an accuracy that can distinguish polymorphs (see the Perspective by Price). They used benzene as a prototypical test case and applied quantum chemical methods that improve estimates of multibody interactions. The results bode well for future applications of theory to optimization of crystallization protocols.

    Science, this issue p. 640; see also p. 619

  13. Superconductivity

    Scattering neutrons asymmetrically

    1. Jelena Stajic

    The crystal structure of solid materials often influences their properties. The more symmetric the structure, the less dependent these properties are on the spatial direction. The superconductors that derive from the compound BaFe2As2 are an exception: Their electronic transport properties can be anisotropic even in the phase where the crystal is symmetric. By scattering neutrons off their samples, Lu et al. found that the magnetic properties of these materials can also be anisotropic. The similar temperature and doping dependence of the anisotropies of both transport and magnetic properties suggests that they may have a common cause.

    Science, this issue p. 657

  14. Nitrogen Cycling

    How microbes compete for nitrate

    1. Nicholas S. Wigginton

    Much of the ammonia fertilizer we use ends up in surface or coastal waters as nitrate. This runoff lowers water quality and damages ecosystems. Although microbial nitrogen respiration influences the fate of nitrate, it is unclear which environmental factors exert the most control. Kraft et al. performed multiple long-term incubation studies of microbial communities from marine sediments. The relative supply of nitrate and nitrite, as well as total carbon and nitrogen, provided selective pressures that drove communities toward denitrification or ammonification. The average generation time of the community also strongly influenced which respiration pathway dominated.

    Science, this issue p. 676

  15. Inflammation

    Bad cholesterol: Bad for bacteria, too?

    1. Kristen L. Mueller

    Why do viral infections, such as the common cold, leave people more susceptible to bacterial pneumonia? One reason is that type I interferons, secreted proteins that initiate antiviral immune responses, suppress other inflammatory molecules that protect against bacterial infection. Reboldi et al. investigated how this suppression occurs on a molecular level in mice. Interferons stimulated expression of a particular enzyme that catalyzes the production of the oxysterol 25-hydroxycholesterol (25-HC). 25-HC inhibits the function of the transcription factor SREBP, which normally drives expression of the gene that encodes interleukin-1, a secreted inflammatory protein with wide-ranging antibacterial functions.

    Science, this issue p. 679

  16. Lipid Cell Biology

    Bending the benefits of polyunsaturates

    1. Stella M. Hurtley

    We have often heard that it is beneficial to eat polyunsaturated fatty acids. We also know that some organelles such as synaptic vesicles are extremely rich in polyunsaturated lipids. However, what polyunsaturated lipids do in our body is unclear. Using cell biology, biochemical reconstitutions, and molecular dynamics, Pinot et al. show that polyunsaturated phospholipids can change the response of membranes to proteins involved in membrane curvature sensing, membrane shaping, and membrane fission. Polyunsaturated phospholipids make the plasma membrane more amenable to deformation; facilitate endocytosis; and, in reconstitution experiments, increased membrane fission by the dynamin-endophilin complex.

    Science, this issue p. 693

  17. Structural Biology

    Going from a trickle to a flood?

    1. Julia Fahrenkamp-Uppenbrink

    Scientists often use x-ray crystallography or nuclear magnetic resonance spectroscopy to determine the three-dimensional structures of proteins, but these methods do not always work well for large protein complexes. In a Perspective, Smith and Rubinstein explain that electron microscopy, when performed at very low temperatures, can now yield very detailed structures of such protein complexes. Many structural biologists used to deride the method, called electron cryo-micoscopy, as “blobology” because it provided limited detail. Now, advances in detector technology and computer processing have lifted blobology into the realm of high-resolution techniques. The recent trickle of high-resolution structures from this method may soon become a flood.

    Science, this issue p. 617

  18. Immunology

    Two signals for maximal T cell activation

    1. Nancy R. Gough

    T cell activation requires increased intracellular calcium and the activity of various enzymes, such as the kinase Itk. Wang et al. report that two signals, calcium and lipids, converged on Itk for maximal activation of T cells. The same region of the Itk protein bound to the signaling lipid PI(3,4,5)P3 and to the calcium-binding protein calmodulin. PI(3,4,5)P3 and calmodulin enhanced the binding of each other to Itk. The binding of both PI(3,4,5)P3 and calmodulin was necessary so that T cells produced maximal levels of an inflammatory cytokine, interleukin-17A.

    Sci. Signal. 7, ra74 (2014).