This Week in Science

Science  07 Oct 2016:
Vol. 354, Issue 6308, pp. 77
  1. Structural Biology

    The long and winding road to methane

    1. Nicholas S. Wigginton

    Archaea make methane with a tungsten-containing enzyme.

    CREDIT: KEVIN SCHAFER/ALAMY STOCK PHOTO

    The process by which archaea make methane involves a series of reactions and enzymes. First, CO2 and methanofuran (MFR) are reduced to formyl-MFR by an as yet unresolved mechanism. Wagner et al. solved the x-ray crystal structure of a tungsten-containing formyl-MFR dehydrogenase complex. Two active sites in the complex are separated by a 43-Å tunnel, which is responsible for transferring the formate made after CO2 reduction. The complex also contains a chain of 46 iron-sulfur clusters. Although the exact function of this chain is unclear, it may electronically couple the four tungsten redox centers.

    Science, this issue p. 114

  2. Neurodevelopment

    Building the human brain

    1. Pamela J. Hines

    As the brain develops, neurons migrate from zones of proliferation to their final locations, where they begin to build circuits. Paredes et al. have discovered that shortly after birth, a group of neurons that proliferates near the ventricles migrates in chains alongside circulatory vessels into the frontal lobes (see the Perspective by McKenzie and Fishell). Young neurons that migrate postnatally into the anterior cingulate cortex then develop features of inhibitory interneurons. The number of migratory cells decreases over the first 7 months of life, and by 2 years of age, migratory cells are not evident. Any damage during migration, such as hypoxia, may affect the child's subsequent physical and behavioral development.

    Science, this issue p. 81; see also p. 38

  3. Biocatalysis

    Something like the real thing

    1. Nicholas S. Wigginton

    Artificial metalloenzymes ideally combine the favorable properties of natural enzymes with the high efficiency of synthetic catalysts. Inserting new metal groups into existing native proteins, however, often leads to poorer overall catalytic efficiency. To break through this limitation, Dydio et al. replaced the iron in the heme group of cytochrome P450 with iridium and subjected it to directed evolution. The enzyme catalyzed a range of reactions with kinetics similar to those of the native enzyme. It was also able to functionalize fully unactivated C-H bonds, a reaction that previously has only been mediated by synthetic catalysts. Moreover, the artificial enzyme was stable across temperatures and scales that are used industrially.

    Science, this issue p. 102

  4. Cognition

    Apes understand false beliefs

    1. Sacha Vignieri

    We humans tend to believe that our cognitive skills are unique, not only in degree, but also in kind. The more closely we look at other species, however, the clearer it becomes that the difference is one of degree. Krupenye et al. show that three different species of apes are able to anticipate that others may have mistaken beliefs about a situation (see the Perspective by de Waal). The apes appear to understand that individuals have different perceptions about the world, thus overturning the human-only paradigm of the theory of mind.

    Science, this issue p. 110; see also p. 39

  5. Solar Cells

    Maintaining a stable phase

    1. Phil Szuromi

    For solar cell applications, all-inorganic perovskite phases could be more stable than those containing organic cations. But the band gaps of the former, which determine the electrical conductivity of these materials, are not well matched to the solar spectrum. The cubic structure of CsPbI3 is an exception, but it is stable in bulk only at high temperatures. Swarnkar et al. show that surfactant-coated α-CsPbI3 quantum dots are stable at ambient conditions and have tunable band gaps in the visible range. Thin films of these materials can be made by spin coating with an antisolvent technique to minimize surfactant loss. When used in solar cells, these films have efficiencies exceeding 10%, making them promising for light harvesting or for LEDs.

    Science, this issue p. 92

  6. Geophysics

    Earthquakes get a more flexible source

    1. Brent Grocholski

    Earth's surface deforms in part as a result of ruptures along brittle crustal faults that generate earthquakes. Understanding rock deformation in the ductile lower crust and mantle is challenging. Using the densest seismic arrays in the world, Inbal et al. have found an unexpected localization of seismicity at these depths under the Newport-Inglewood fault in southern California. The seismicity points to a type of earthquake that may help us understand how ductile deformation operates in this region of Earth.

    Deep ductile deformation in the lower crust causes localized seismicity.

    PHOTO: ASHLEY COOPER PICS/ALAMY STOCK PHOTO

    Science, this issue p. 88

  7. Water Supply

    Megadrought risk in the American Southwest

    1. Kip Hodges

    Prolonged droughts have long-term negative effects on water resources and agricultural productivity. Such events can be particularly devastating in regions such as the American Southwest, where fresh water is in short supply. Ault et al. are able to predict megadrought risk in that region based on how the moisture balance at Earth's surface responds to precipitation and temperature changes simulated by climate models. The findings are alarming, but the authors suggest that dramatic reductions in greenhouse gas emissions could cut megadrought risk by half.

    Sci. Adv. 10.1126.sciadv.1600873 (2016).

  8. Cancer

    More than a FLT-ing success in leukemia

    1. Yevgeniya Nusinovich

    Acute myeloid leukemia is a difficult disease to treat under the best of circumstances, and the subtype containing internal tandem duplication of fms-like tyrosine kinase 3 (FLT3-ITD) is particularly challenging. In a high-throughput drug screen, Lam et al. identified homoharringtonine as a candidate treatment for this type of leukemia and confirmed its effectiveness in cancer cells, mouse models, and patients. Promising results were obtained from a phase II clinical trial that included elderly patients and patients for whom all previous treatments had failed.

    Sci. Transl. Med. 8, 359ra129 (2016).

  9. Health Economics

    Delivering health care to mystery patients

    1. Gilbert Chin

    Many families in developing countries do not have access to medical doctors and instead receive health care from informal providers. Das et al. used “mystery” patients (trained actors) to test whether a 9-month training program improved the quality of care delivered by informal providers in West Bengal (see the Perspective by Powell-Jackson). The patients did not identify themselves to the providers and were not told which providers had participated in the training program. The results of this blinded assessment showed that medical doctors delivered better care than informal providers but that the training program closed much of the gap.

    Science, this issue p. 80; see also p. 34

  10. Cell Death

    DNA damage-activated nuclease identified

    1. L. Bryan Ray

    Cells that experience stresses and accumulate excessive damage to DNA undergo cell death mediated by a nuclear enzyme known as PARP-1. During this process, apoptosis-inducing factor (AIF) translocates to the nucleus and activates one or more nucleases to cleave DNA. Wang et al. found that macrophage migration inhibitory factor (MIF) is an AIF-associated endonuclease that contributes to PARP-1-induced DNA fragmentation (see the Perspective by Jonas). In mouse neurons in culture, loss of MIF protected neurons from cell death caused by excessive stimulation. Targeting MIF could thus provide a therapeutic strategy against diseases in which PARP-1 activation is excessive.

    Science, this issue p. 82; see also p. 36

  11. Quantum Simulation

    Spin-orbit coupling in an optical lattice

    1. Jelena Stajic

    Studying topological matter in cold-atom systems may bring fresh insights, thanks to the intrinsic purity and controllability of this experimental setting. However, the necessary spin-orbit coupling can be tricky to engineer. Wu et al. conceived and experimentally demonstrated a simple scheme that involves only a single laser source and can be continuously tuned between one- and two-dimensional spin-orbit coupling (see the Perspective by Aidelsburger). Although this experiment used bosonic atoms, it is expected that the setup would also work for fermions.

    Science, this issue p. 83; see also p. 35

  12. Quantum Gases

    Sluggish turmoil in the Fermi sea

    1. Jelena Stajic

    The nonequilibrium dynamics of many-body quantum systems are tricky to study experimentally or theoretically. As an experimental setting, dilute atomic gases offer an advantage over electrons in metals. In this environment, the heavier atoms make collective processes that involve the entire Fermi sea occur at the sluggish time scale of microseconds. Cetina et al. studied these dynamics by using a small cloud of 40K atoms that was positioned at the center of a far larger 6Li cloud. Controlling the interactions between K and Li atoms enabled a detailed look into the formation of quasiparticles associated with K “impurity” atoms.

    Science, this issue p. 96

  13. Device Technology

    A flatter route to shorter channels

    1. Phil Szuromi

    High-performance silicon transistors can have gate lengths as short as 5 nm before source-drain tunneling and loss of electrostatic control lead to unacceptable leakage current when the device is off. Desai et al. explored the use of MoS2 as a channel material, given that its electronic properties as thin layers should limit such leakage. A transistor with a 1-nm physical gate was constructed with a MoS2 bilayer channel and a single-walled carbon nanotube gate electrode. Excellent switching characteristics and an on-off state current ratio of ∼106 were observed.

    Science, this issue p. 99

  14. Bioinspired Materials

    Making nacre shine in the lab

    1. Nicholas S. Wigginton

    Many of the materials that animals use to make shells and skeletons are built with brittle or soft molecules. They owe their amazing mechanical properties to their layered construction, which is a challenge for synthetic fabrication. Pearly nacre, for example, has proved challenging to make owing to its complex structure of aragonite crystals in an organic matrix. Using an assembly-and-mineralization approach, Mao et al. have managed to fabricate nacre in the laboratory (see the Perspective by Barthelat). First, a layered, three-dimensional chitosan matrix is made, within which aragonite nanocrystals are precipitated from a solution containing calcium bicarbonate.

    Science, this issue p. 107; see also p. 32

  15. Viral Infection

    Kinase inhibitors for viral encephalitis

    1. Nancy R. Gough

    Japanese encephalitis virus (JEV) is a mosquito-transmitted flavivirus related to dengue, West Nile, and Zika viruses. The neuroinflammation and severe neurological damage caused by JEV infection can be fatal. Ye et al. found that inhibiting kinase signaling pathways reduced inflammatory responses by infected glial cells in culture. Treating infected mice with a JNK kinase inhibitor improved survival and limited neuroinflammation and neuronal death. This strategy offers promise for treating JEV and other neurogenic viruses.

    Sci. Signal. 9, ra98 (2016).