This Week in Science

Science  20 May 2016:
Vol. 352, Issue 6288, pp. 949
  1. Catalysis

    How zinc helps copper make methanol

    1. Phil Szuromi
    PHOTO: KULD ET AL.

    Copper nanoparticles can catalyze the formation of methanol from a mixture of CO2, CO, and H2, but adding zinc oxide nanoparticles, themselves inactive in this reaction, greatly boosts the rates. Kuld et al. measured how methanol synthesis activity varies with the coverage of zinc atoms on the copper nanoparticles, as determined experimentally and with density functional theory calculations. The ZnO nanoparticle size determined how much zinc covers the copper surface and in turn controlled the catalyst activity.

    Science, this issue p. 969

  2. Synapse Formation

    Synapse identity through specific splicing

    1. Peter Stern

    What are the mechanisms that create different, highly specific types of synapses? Traunmüller et al. found that the RNA-binding protein SLM2 regulated a very small number of alternative splicing decisions in mouse hippocampal neurons. Disrupting this splicing program resulted in specific defects in transsynaptic protein complexes. Glutamatergic transmission and synaptic plasticity were impaired. Genetically restoring one single alternative splicing event was enough to recover synaptic plasticity. SLM2 thus activates a highly specific alternative splicing program that controls the properties of glutamatergic synapses.

    Science, this issue p. 982

  3. HIV-1 Antibodies

    Insights into antibody therapy for HIV-1

    1. Kristen L. Mueller

    Despite the success of antiretroviral therapy, HIV-1-infected individuals still harbor latent virus. Thus, other therapeutic strategies are needed. A single injection of a broad and potent monoclonal antibody targeting the HIV-1 envelope protein reduced viral loads in HIV-1-infected individuals, albeit only transiently. Lu et al. now report that antibody treatment not only blocked free virus from infecting new cells, it also accelerated the clearance of infected cells. Furthermore, Schoofs et al. demonstrate that therapeutic antibody treatment enhanced infected individuals' humoral response against the virus. Thus, neutralizing antibodies may be a promising therapy for HIV-1 because of their potential to reduce the viral reservoir.

    Science, this issue pp. 1001 and 997

  4. Developmental Biology

    The TRIC to building strong bones

    1. Annalisa M. VanHook

    Osteoblasts are bone-building cells that secrete a collagen-rich matrix required for bone formation. Defects in collagen deposition cause the brittle bones that are characteristic of osteogenesis imperfecta. Zhao et al. found that mice lacking Tric-b, which encodes a cation channel in the endoplasmic reticulum (ER), had brittle bones similar to those of osteogenesis imperfecta patients. The collagen synthesized by osteoblasts in Tric-b knockout mice was not secreted, but instead accumulated inside the cells and triggered ER stress. Thus, TRIC-B may be necessary to prevent ER stress in osteoblasts so that they can secrete the large amounts of collagen required to build bones.

    Sci. Signal. 9, ra49 (2016).

  5. Artificial Spin Ice

    From a bar to a charge, magnetically

    1. Jelena Stajic

    Artificial spin ices are arrays of nanoscale bar magnets that can mimic the behavior of naturally occurring “frustrated” magnetic materials. Usually the arrays take the form of a square lattice with the bar magnets perpendicular to its sides. Wang et al. “broke up” each bar into a positive and negative magnetic charge. Working backward from an array of these charges, they designed a structure that has bar magnets oriented not only perpendicularly to the sides of the square lattice but also diagonally. Compared to the traditional one, this structure was much more controllable by global and local magnetic fields.

    Science, this issue p. 962

  6. Robotics

    Making small robots stick

    1. Marc S. Lavine

    Tiny robots can spy from a leaf.

    CREDIT: SECOND BAY STUDIOS

    Aerial views offer the chance to observe a wide range of terrain at once, but they come at the cost of needing to stay aloft. Graule et al. found that electrostatic forces could keep their insect-sized flying robot stuck to the underside of a range of surfaces (see the Perspective by Kovac). They mounted an electrostatically charged pad to the top of their robot, which could then reversibly stick to existing elevated perches—including a leaf—using less power than would be needed for sustained flight.

    Science, this issue p. 978; see also p. 895

  7. DNA Repair

    A starvation survival signal fights DNA damage

    1. Guy Riddihough

    The alarmone guanosine-3′,5′-(bis)pyrophosphate (ppGpp) shuts down transcription in bacteria that are starving. This “stringent response” helps them conserve energy and survive adverse conditions. Kamarthapu et al. show that ppGpp is also essential for DNA repair. ppGpp couples transcription elongation to the nucleotide excision repair pathway. ppGpp helps backtrack the RNA polymerase away from the DNA damage to facilitate repair. Through inhibiting DNA replication, it also avoids dangerous collisions between the replication fork and backtracked RNA polymerase.

    Science, this issue p. 993

  8. Dynamic Cytoskeleton

    Making the fast faster still

    1. Stella M. Hurtley

    Coordination between actin and microtubule cytoskeleton dynamics is critical during cell migration, phagocytosis, cytokinesis, and embryogenesis. However, the basis for cross-regulation of cytoskeleton dynamics is unclear. Henty-Ridilla et al. found that a component of the microtubule cytoskeleton accelerates actin filament elongation and protects the growing actin filament end (see the Perspective by Rottner). Thus, growing microtubules appear to be able to directly control the actin assembly machinery and actin filament dynamics.

    Science, this issue p. 1004; see also p. 894

  9. Graft-vs-Host

    Antibiotics: A double-edged sword

    1. Orla M. Smith

    Patients undergoing allogeneic hematopoietic stem cell transplantation often receive antibiotics for infections, which unfortunately also kill intestinal bacteria. These symbiotic bacteria in the gut do not normally cause disease and are thought to suppress inflammation. Shono et al. examined the records of 857 transplant patients and found that certain antibiotics were linked with development of graft-versus-host disease (GVHD), which can cause severe intestinal inflammation. In a mouse model, these antibiotics appeared to select for bacteria that consume intestinal mucus, damaging this important protective layer and exacerbating GVHD.

    Sci. Transl. Med. 8, 339a71 (2016).

  10. Cancer Immunotherapy

    Another pathway to cancer resistance

    1. Kristen L. Mueller

    Therapies targeting the tumor microenvironment show promise for treating cancer. For example, antibodies targeting colony-stimulating factor-1 receptor (CSF-1R) inhibit protumorigenic macrophages and regress tumors in mouse models of glioblastoma multiforme (GBM), a deadly form of brain cancer. Quail et al. found that although CSR-1R blockade prolonged survival in mouse models of GBM, more than 50% of tumors eventually recurred. Recurrence was correlated with elevated PI3-K activity in tumors, driven by macrophage-secreted IGF-1. Blocking PI3-K and IGF-1 signaling in rebounding tumors prolonged survival. Thus, tumors can acquire resistance to therapy through intrinsic changes and through changes in their microenvironment.

    Science, this issue p. 10.1126/science.aad3018

  11. Superconductivity

    Discerning the nematic connection

    1. Jelena Stajic

    The phase diagram of any given family of iron-based superconductors is complicated: Superconductivity competes with antiferromagnetism, with a structural transition often thrown in for good measure. Transport experiments have shown that in one of these families, Ba(Fe1-xCox)2As2, a rotational electronic asymmetry, dubbed nematicity, drives the structural transition. Kuo et al. detected nematic fluctuations in five Fe-based superconductor families in the vicinity of optimal chemical doping: the doping that maximizes the superconducting transition temperature. Thus, nematicity may play a role in the mechanism of superconductivity in these compounds.

    Science, this issue p. 958

  12. Superconductivity

    Making a graphene super-edge

    1. Jelena Stajic

    In superconductors, the electrical current is carried by “Cooper pairs,” formed out of an electron and a hole. This supercurrent will happily cross a thin barrier between two superconductors. But what if a strong magnetic field were applied at the barrier, forcing charge carriers to travel only along the edge of the barrier? Amet et al. explored this regime in a sample consisting of two superconducting electrodes and a graphene barrier under magnetic fields of up to 2 tesla (see the Perspective by Mason). Their transport measurements were consistent with a model in which the supercurrent was carried by the edge states in graphene.

    Science, this issue p. 966; see also p. 891

  13. Plant Science

    Peptide domain links phosphate need to uptake

    1. Pamela J. Hines

    Cellular phosphate (Pi) levels are tightly controlled, but it is not clear how eukaryotic cells actually “measure” the concentration of Pi. Wild et al. now show that inositol polyphosphate (InsP) signaling molecules regulate Pi homeostasis in fungi, plants, and humans by interacting with SPX-domain-containing proteins. SPX domains are found in many eukaryotic Pi transporters, Pi-regulated enzymes, and signaling proteins. InsP binding allowed SPX domains to interact with different target proteins. In plants, one such target protein is a transcription factor. During normal growth, high levels of InsP promoted formation of a SPX protein-transcription factor complex. Under Pi starvation, InsP levels dropped, releasing the transcription factor to promote Pi starvation-response gene transcription.

    Science, this issue p. 986

  14. Signal Transduction

    The secrets of making signaling responsive

    1. L. Bryan Ray

    Many receptor proteins that respond to biological signals form multimeric complexes, which gives them more sophisticated regulatory properties than those of simple one-to-one binding reactions. Ha et al. describe how the binding of multiple ligands to receptor complexes can generate threshold effects and switch-like ultrasensitivity. If binding of the first ligand makes binding of a second less likely (a property known as negative cooperativity), and binding can also deplete the total amount of ligand present, the way the system responds to various doses of the ligand can change dramatically from a very gradual one to a switch-like behavior. The authors provide theory and experiments that explain how such systems function and may be suited to biological regulation.

    Science, this issue p. 990

  15. Gene Evolution

    Evolutionary maintenance of gene duplications

    1. Laura M. Zahn

    Understanding genetic redundancy—the maintenance of multiple copies of a gene after duplication—and its relevance to genetic evolution have long been debated. Lan and Pritchard examined gene duplicates within human and other mammalian genomes. The expression of genes appears to be controlled by dosage balance and tight coregulation of tandem duplicates. They found little evidence for gene copies evincing significantly different expression patterns. However, such changes can evolve later, after gene copies become physically separated within the genome and thus are no longer jointly regulated.

    Science, this issue p. 1009

  16. Nanotechnology

    DNA gatekeepers

    1. Julia Fahrenkamp-Uppenbrink

    In biological systems, membrane proteins regulate flow into and out of cells and play key roles in cell signaling and shaping cell morphology. Scientists are now using DNA to create synthetic mimics of these proteins. In a Perspective, Howorka explains that the three-dimensional structures of the DNA units are easier to manipulate than those of their protein-based counterparts. The resulting structures are also larger, an important factor when using them to stabilize vesicles for bioimaging and drug delivery. The DNA nanostructures can also tune membrane fluidity and bind proteins in defined positions for cell-biological studies. Using DNA in this counterintuitive way opens up possibilities in synthetic biology.

    Science, this issue p. 890

  17. Enzyme Mechanisms

    A radical route to making methane

    1. Nicholas S. Wigginton

    Microorganisms are the main drivers of Earth's methane cycle. The enzyme ultimately responsible for biological methane production has an ambiguous mechanism because it involves difficult-to-isolate reaction intermediates. Wongnate et al. used stopped-flow and rapid freeze-quench experiments to trap a methyl radical in the active site of methyl-coenzyme M reductase (see the Perspective by Lawton and Rosenzweig). Spectroscopy demonstrated that cofactor F430 contained Ni(II), consistent with computational results. The final step of methanogenesis thus proceeds through Ni(II)-thiolate and methyl radical intermediates rather than an organometallic methyl-Ni(III) mechanism.

    Science, this issue p. 953;, see also p. 892

  18. Catalysis

    Tough core-shell catalysts

    1. Phil Szuromi

    One approach for increasing the activity of precious metals in catalysis is to coat them onto less expensive earth-abundant transition metal cores such as nickel, but often these structures alloy and deactivate during reactions. Hunt et al. synthesized several types of transition metal carbide nanoparticles coated with atomically thin precious-metal shells. Titanium-doped tungsten carbide nanoparticles with platinum-ruthenium shells were highly active for methanol electrooxidation, stable over 10,000 cycles, and resistant to CO deactivation.

    Science, this issue p. 974