This Week in Science

Science  03 Jul 2015:
Vol. 349, Issue 6243, pp. 42
  1. Physics

    Designing mechanical complexity

    1. Ian S. Osborne
    Mechanical pendulasIMAGE: HEIDI HOSTETTLER

    The quantum properties of topological insulators translate to mechanical systems governed by Newton's equations of motion. Many-body interactions and the multiple degrees of freedom available to charge carriers give electronic systems a range of exotic behaviors. Süsstrunk and Huber show that this extends to mechanical systems made up of a large lattice of coupled pendula. Mechanical excitations can be eliminated from the inner part of the lattice and confined to the edges, much like topological insulators. In addition to presenting a tractable toy system in which to study complex phenomena, the approach has potential uses in vibration isolation.

    Science, this issue p. 47

  2. Brain Structure

    The best way to fold a mammalian brain

    1. Peter Stern

    As mammalian brains grew larger through evolution, the organization and folding of brains changed too. In a series of statistical analyses comparing a large number of mammalian species, Mota and Herculano-Houzel found that brain folding is not simply a phylogenetic consequence of brain mass increase (see the Perspective by Striedter and Srinivasan). The exposed surface of the cortex scales across all mammals and across individuals as a single power law of the product of total cortical surface and the square root of cortical thickness.

    Science, this issue p. 74; see also p. 31

  3. Influenza

    Immunological mistaken identity

    1. Angela Colmone

    The incidence of narcolepsy increased after the global vaccination campaign against the 2009 A/H1N1 influenza pandemic, but only in some countries. Ahmed et al. examined the protein content of the vaccines used by country. One notable peptide within an influenza protein (nucleopeptide A) shared residues with human hypocretin receptor 2, which has been linked to narcolepsy. Patients who developed narcolepsy after being vaccinated produced antibodies that cross-reacted to both the influenza and the hypocretin receptor 2 epitopes. The vaccine used in countries without new narcolepsy cases contained lower levels of nucleoprotein A.

    Sci. Transl. Med. 7, 294ra105 (2015).

  4. Metalloproteins

    Nickel pincers as enzyme cofactors

    1. Nicholas S. Wigginton

    Organometallic nickel complexes long synthesized in the laboratory exist naturally in enzymes as well. Desguin et al. determined the structure and metal-binding residues of the Ni-containing active site in bacterial lactate racemase (see the Perspective by Zamble). A dithiodinicotinic acid mononucleotide derivative cofactor binds Ni through sulfur and carbon bonds, resembling synthetic nickel pincer complexes. Genes encoding accessory proteins involved in the synthesis of this cofactor are widely distributed in other bacteria, suggesting its involvement in other enzymes.

    Science, this issue p. 66; see also p. 35

  5. Plant Volatiles

    Stop to smell the roses

    1. Pamela J. Hines

    Some roses smell beautiful, yet others only look beautiful. Magnard et al. leveraged this distinction to study the biosynthesis of geraniol, a monoterpene alcohol in rose scent (see the Perspective by Tholl and Gershenzon). Enzymes known for geraniol synthesis in other plants, such as basil, did not seem to provide that function for roses. Instead, a diphosphohydrolase, which functions in the cytoplasm of cells in rose petals, generates the geraniol emitted by fragrant roses. Identification of the enzyme and its gene enables marker-assisted breeding to put the perfume back into beauty.

    Science, this issue p. 81; see also p. 28

  6. Plant Genomics

    Signatures of adaptation in the field

    1. Barry Pogson

    Sorghum genomes show signs of adaptation

    PHOTO: DSZC/ISTOCKPHOTO

    Adaptation to the environment is critical for the survival of all species. For crops, this can be confounded or enhanced by farmers and breeders selecting for particular traits. To determine the associations between genes and local environments, Lasky et al. performed a global genetic survey of nearly 2000 regional varieties of domesticated sorghum. Regional environmental stresses such as climate and soil type were major determinants of adaptation. Enhancing sorghum (a staple crop for 500 million people in sub-Saharan Africa and Asia) and other crops may be possible based on marker-assisted selection of adaptive traits.

    Sci. Adv. 10.1126/sciadv.1400218 (2015).

  7. Conservation

    Focused on protecting a few

    1. Sacha Vignieri

    The illegal ivory trade threatens the persistence of stable wild elephant populations. The underground and covert nature of poaching makes it difficult to police. Wasser et al. used genetic tools to identify the origins of elephant tusks seized during transit (see the Perspective by Hoelzel). The majority of source animals were part of just a few wild elephant populations in Africa—and just two areas since 2006. Increased focus on enforcement in a few such areas could help interrupt poaching activities and restore wild elephant populations.

    Science, this issue p. 84; see also p. 34

  8. Porous Materials

    Laser patterning polymer membranes

    1. Marc S. Lavine

    Porous materials are useful for membranes, filters, energy conversion, and catalysis. Their utility often depends on the ability to finely control both the pore sizes and their connectivity. Tan et al. prepared porous thin films of block copolymers mixed with phenol-formaldehyde resins (resols) on silicon substrates using a simple laser process. On exposure to ultraviolet light, rapid heating of the substrate causes polymerization of the resols and decomposition of the block copolymer. This method allows direct patterning of the films on a local scale, with tunable pore sizes and size distributions.

    Science, this issue p. 54

  9. Oceanography

    Carbon emissions and their ocean impacts

    1. H. Jesse Smith

    Anthropogenic CO2 emissions directly affect atmospheric chemistry but also have a strong influence on the oceans. Gattuso et al. review how the physics, chemistry, and ecology of the oceans might be affected based on two CO2 emission trajectories: one business as usual and one with aggressive reductions. Ocean warming, acidification, sea-level rise, and the expansion of oxygen minimum zones will continue to have distinct impacts on marine communities and ecosystems. The path that humanity takes regarding CO2 emissions will largely determine the severity of these phenomena.

    Science, this issue 10.1126/science.aac4722

  10. Organic Chemistry

    Elaborate amines from commodity olefins

    1. Jake Yeston

    Fine spatial control over the formation of carbon-nitrogen bonds is essential to the synthesis of many pharmaceutical and agrochemical compounds. Yang et al. synthesized a copper catalyst that shows exceptional discrimination between similar substituents in the addition of N-H bonds across the C-C double bonds of simple olefins. In particular, the catalyst favors one of two mirror-image products that differ in the relative orientations of methyl and ethyl groups. This selectivity fosters the use of readily available commodity olefins in the preparation of complex chiral amines.

    Science, this issue p. 62

  11. Biomechanics

    The curious tale of the square tail

    1. Marc S. Lavine

    Appendages in animals are typically round, but the seahorse tail has a square cross section. Porter et al. hypothesize that this shape provides better functionality and strength than a round cross section (see the Perspective by Ashley-Ross). Three-dimensional printed models show that square cross section shapes behave more advantageously when subjected to compressive forces. By allowing greater deformation without damage and accommodating twisting deformations, square appendages passively return to their original configurations. The added flexibility of the square cross section enhances the tail's ability to grasp objects.

    Science, this issue 10.1126/science.aaa6683; see also p. 30

  12. Sulfur Chemistry

    An unexpected gaseous sulfur species

    1. Jake Yeston

    Sulfuric acid plays a central role in both industrial and atmospheric contexts. As such, the behavior of SO3 mixtures in gas phases has been studied for over a century. In gas-phase experiments on wet SO3 and formic acid, Mackenzie et al. discovered a previously unrecognized covalent adduct: formic sulfuric anhydride, or HC(O)OSO3H. The combination of microwave spectroscopy and theoretical calculations reveals its structural properties. The compound may play a role in the nucleation of atmospheric aerosols by serving as an intermediate to H2SO4 formation.

    Science, this issue p. 58

  13. Presynaptic Networks

    Tracing cells that project to one neuron

    1. Peter Stern

    Feature extraction is a prominent characteristic of cortical neurons involved in the early stages of sensory processing. Wertz et al. retrogradely marked an injected neuron and its direct inputs to reveal the network mechanisms that mediate their response. Neurons within each presynaptic network layer of single direction-selective cells showed similar motion direction preferences. In some networks, layer-specific functional modules were identical to the orientation preference of the postsynaptic neuron. Presynaptic neurons, however, displayed a general bias toward the stimulus feature that elicited a response in the postsynaptic neuron.

    Science, this issue p. 70

  14. Green Chemistry

    Synthesizing more sustainable plastics

    1. Nicholas S. Wigginton

    Zeolites can help synthesize cheaper plastic precursors from biologically sourced feedstocks. Producing sustainable plastics must compete with more cost-effective petrochemical-based synthesis routes. Dusselier et al. developed a zeolite-based strategy to catalyze the transformation of microbially produced lactic acid into lactide, a difficult-to-synthesize precursor of biodegradable polylactic acid plastics. The selectivity of nearly 80% is based on active site spatial confinement in the zeolite micropores. This step substantially simplifies current high-cost synthesis routes and generates nearly zero waste using current reactor technologies.

    Science, this issue p. 78

  15. Selenoproteins

    Clearing out selenoprotein garbage

    1. Guy Riddihough

    Our DNA consists of codons that code for 20 different amino acids. Another amino acid, selenocysteine, is also found in several human selenoproteins. Selenocysteine is incorporated through the recoding of a stop codon, but failures in this process result in premature termination of protein synthesis. Lin et al. showed that the potentially dangerous truncated proteins formed in such cases are specifically degraded by a protein quality surveillance system. The surveillance system can specifically recognize the truncated ends of the various prematurely terminated selenoproteins and target their destruction.

    Science, this issue p. 91

  16. Dengue Virus

    An antibody to lock dengue virus out

    1. Kristen L. Mueller

    Mosquito-borne dengue virus (DENV) is a growing public health threat. Nearly 400 million people are infected annually, and no vaccine is currently available. Fibriansah et al. report that a human antibody (2D22) specific for DENV serotype 2, when given therapeutically, can protect mice from a lethal form of this virus. Structural analysis revealed that 2D22 binds across multiple DENV envelope proteins, which probably blocks the ability of these proteins to assemble into the orientation necessary for viral entry. The epitope where 2D22 binds to the virus may therefore represent a potential vaccine target.

    Science, this issue p. 88

  17. Neuroscience

    Keeping immature neurons excited

    1. Nancy R. Gough

    After birth, signaling by the neurotransmitter GABA in the brain switches from excitatory to inhibitory. GABA mediates both responses by binding to ligand-gated ion channels that conduct Cl. The opening of these channels depends on the concentration of Cl in neurons. Friedel et al. identified phosphorylation events in the K+-Cl cotransporter KCC2 that depended on the activity of the kinase WNK1. These phosphorylation events inhibited KCC2 activity and contributed to the depolarizing effect of GABA-mediated signaling in immature rat neurons by maintaining a high intracellular Cl concentration.

    Sci. Signal. 8, ra65 (2015).

  18. Geomorphology

    Landscape evolution in a sandbox

    1. Brent Grocholski

    The long-term response of hills and valleys to changes in climate depends on a variety of physical factors. Sweeney et al. performed tabletop erosion experiments as a function of rainfall and uplift: variables that are impossible to precisely control in nature (see the Perspective by McCoy). Ridge and valley spacing are set by the balance of sediment moving down hillslopes or being washed out of valleys by rivers. Landscapes therefore evolve as a response to climate change altering erosion rates.

    Science, this issue p. 51; see also p. 32

  19. Structural Virology

    Retroviral capsids in their native form

    1. Kristen L. Mueller

    Capsid proteins of retroviruses form protective lattices around viral RNA molecules. The precise molecular details of how individual, full-length capsid proteins assemble to shield the viral genome; however, are not well understood. Obal et al. and Gres et al. now report high resolution crystal structures of the full length capsid proteins from Bovine Leukemia Virus and HIV-1, respectively. The two studies complement each other to reveal the dynamic nature of capsid protein assembly and of how individual capsid proteins interact in the lattice. The findings may have relevance for drug design.

    Science, this issue p. 95; see also p. 99