This Week in Science

Science  20 Jan 2017:
Vol. 355, Issue 6322, pp. 257
  1. Cardiovascular Disease

    Robots have a change of heart

    1. Caitlin Czajka

    A robotic sleeve supports the pumping heart without contacting the blood.

    CREDIT: QIU ET AL.; HUGH JOHNSON/VISUALS UNLIMITED

    Ventricular assist devices help failing hearts function by pumping blood, but they require monitoring and anticoagulant therapy to prevent blood clot formation. Roche et al. created a soft robotic device with material properties similar to those of native heart tissue that sits snugly around the heart and provides ventricular assistance without ever contacting the blood. The robotic sleeve uses compressed air to power artificial silicone muscles that compress and twist, mimicking the movements of the normal human heart. The device increased cardiac ejection volume in vitro and when implanted in adult pigs during drug-induced cardiac arrest.

    Sci. Transl. Med. 9, eaaf3925 (2017).

  2. Nanomaterials

    Alcohols remove lithium to make nanowires

    1. Marc S. Lavine

    Many existing routes for making metal and metal oxide nanowires are complex, require harsh solvents, or are not easily scaled up. Lei et al. developed an extraction process to remove lithium from aluminum or magnesium alloys by using alcohol solvents. The resulting highly reactive Al or Mg atoms formed alkoxide nanowires, which could be converted into oxides by high-temperature treatment. The authors used this approach to produce Al2O3 separators that enhanced the safety of lithium batteries.

    Science, this issue p. 267

  3. Chemical Physics

    An x-ray view of C–F and S–F bond breaks

    1. Jake Yeston

    X-ray absorption spectroscopy is a useful probe of element-specific dynamics in molecular reactions. However, the required x-ray fluxes have rarely been available outside expensive dedicated facilities such as synchrotrons. Pertot et al. developed a tabletop laser-based high-harmonic source that extends far enough into the x-ray region to probe carbon K-edge and sulfur L-edge absorptions with femtosecond temporal resolution. They used this source to track the previously elusive dissociative dynamics of gaseous carbon tetrafluoride and sulfur hexafluoride after laser-induced ionization.

    Science, this issue p. 264

  4. Plant Science

    Keeping roots water-tight

    1. Pamela J. Hines

    Microscopic view of the root Casparian strip (red)

    CREDIT: ROCHE ET AL.

    The Casparian strip provides a waterproofing function to plant roots, protecting them against unregulated influxes of water and minerals. The integrity of the Casparian strip depends on a receptor-like kinase. Doblas et al. and Nakayama et al. now identify the peptide ligands in the core of the root (the stele) that help regulate Casparian strip formation. The receptor is expressed on the outward-facing surface of the root endodermal cells that surround the stele. When the endodermal layer is sealed by the Casparian strip, the peptide ligands cannot reach their receptors. When the endodermal layer is breached, whether by damage or during development, the peptides reach their receptors and activate signaling that encourages lignin deposition, shoring up the strips.

    Science, this issue p. 280, p. 284

  5. Protein Structure

    Filling in the protein fold picture

    1. Valda Vinson

    Fewer than a third of the 14,849 known protein families have at least one member with an experimentally determined structure. This leaves more than 5000 protein families with no structural information. Protein modeling using residue-residue contacts inferred from evolutionary data has been successful in modeling unknown structures, but it requires large numbers of aligned sequences. Ovchinnikov et al. augmented such sequence alignments with metagenome sequence data (see the Perspective by Söding). They determined the number of sequences required to allow modeling, developed criteria for model quality, and, where possible, improved modeling by matching predicted contacts to known structures. Their method predicted quality structural models for 614 protein families, of which about 140 represent newly discovered protein folds.

    Science, this issue p. 294; see also p. 248

  6. Paleoclimate

    Sea surface temperatures of the past

    1. H. Jesse Smith

    Understanding how warm intervals affected sea level in the past is vital for projecting how human activities will affect it in the future. Hoffman et al. compiled estimates of sea surface temperatures during the last interglacial period, which lasted from about 129,000 to 116,000 years ago. The global mean annual values were ∼0.5°C warmer than they were 150 years ago and indistinguishable from the 1995–2014 mean. This is a sobering point, because sea levels during the last interglacial period were 6 to 9 m higher than they are now.

    Science, this issue p. 276

  7. Protein Homeostasis

    Deciding a protein's fate

    1. Valda Vinson

    Protein synthesis inside cells is finely balanced with protein degradation to maintain homeostasis. Shao et al. show how differential affinities and binding kinetics of three chaperones regulate the fate of tail-anchored (TA) membrane proteins. The chaperone SGTA binds to TA proteins and quickly transfers them to the targeting factor TRC40 through the C-terminal domain of the quality-control module BAG6. Proteins that dissociate from SGTA can either rebind or, at a slower rate, be bound by the C-terminal domain of BAG6. The latter puts them on a path to degradation. This hierarchy means that biosynthesis has the higher priority, but excess free TA proteins are degraded.

    Science, this issue p. 298

  8. Cancer Immunotherapy

    Locking TNFR2 to kill ovarian cancer

    1. Leslie K. Ferrarelli

    The TNF (tumor necrosis factor) ligand family promotes tumor growth and progression. Torrey et al. developed an antibody that locks TNFR2, a TNF receptor found on immunosuppressive regulatory T cells and some tumor cells, in an inactive state (see the Focus by Chen and Oppenheim). The antibody inhibited the proliferation of regulatory T cells while promoting the proliferation of effector T cells isolated from metastatic sites in ovarian cancer patients. The antibody had less of an effect on T cells from normal donors. Thus, this antibody may be more specific and less toxic than current antibodies against TNFRs.

    Sci. Signal. 10, eaaf8608, eaal2328 (2017).

  9. Enzyme Dynamics

    Working as a pair

    1. Valda Vinson

    Enzymes provide scaffolds that facilitate chemical reactions. Enzyme dynamics often enhance reactivity by allowing the enzyme to sample the transition state between reactants and products. Kim et al. explored the role of dynamics in the dimeric enzyme fluoroacetate dehalogenase (see the Perspective by Saleh and Kalodimos). They found that the two protomers are asymmetric, with only one being able to bind substrate at a time. The nonbinding protomer contributed to catalysis by becoming more dynamic to compensate for the entropy loss of its partner.

    Science, this issue 10.1126/science.aag2355; see also p. 247

  10. Organoids

    Ethics of organoid research

    1. Beverly A. Purnell

    Growing functional human tissues and organs would provide much needed material for regeneration and repair. New technologies are taking us in that direction. In addition to their use in regenerative medicine, stem cells that grow and morph into organ-like structures known as organoids can be used in drug development and toxicology testing. The potential developments and possibilities are numerous and affect not only biomedicine but also areas of ongoing ethical debate, such as animal experimentation, research on human embryos and fetuses, ethics review, and patient consent. Bredenoord et al. review how organoids affect existing ethical debates and how they raise novel ethical dilemmas and professional responsibilities.

    Science, this issue 10.1126/science.aaf9414

  11. Cancer

    Chromosomal chaos and tumor immunity

    1. Paula A. Kiberstis

    Cancer immunotherapy produces durable clinical responses in only a subset of patients. Identification of tumor characteristics that correlate with responses could lead to predictive biomarkers and shed light on causal mechanisms. Davoli et al. found that human tumors with extensive aneuploidy—i.e., that display a highly abnormal number of chromosomes and chromosomal segments—express fewer markers of the immune cells responsible for tumor destruction. In a retrospective analysis of clinical trial data, they found that melanoma patients with highly aneuploid tumors were less likely to benefit from immune checkpoint blockade therapy than patients whose tumors had a more normal karyotype. Thus, aneuploidy appears to enhance the ability of tumors to evade the immune system.

    Science, this issue 10.1126/science.aaf8399

  12. Chromatin

    Deformation powers the nucleosome slide

    1. Guy Riddihough

    In eukaryotes, DNA is packed onto nucleosomes. For transcription factors and other proteins to gain access to DNA, nucleosomes must be moved out of the way, or “remodeled”—but not disassembled. Nucleosomes are composed of histone protein octamers, the cores of which have generally been considered to be fairly rigid. Sinha et al. used nuclear magnetic resonance and protein cross-linking to show that one of the enzyme complexes that remodel nucleosomes, SNF2h, is able to distort the histone octamer (see the Perspective by Flaus and Owen-Hughes). Nucleosome deformation was important for this remodeler to be able to slide nucleosomes out of the way.

    Science, this issue 10.1126/science.aaa3761; see also p. 245

  13. Device Technology

    Moving transistors downscale

    1. Phil Szuromi

    One option for extending the performance of complementary metal-oxide semiconductor (CMOS) devices based on silicon technology is to use semiconducting carbon nanotubes as the gates. Qiu et al. fabricated top-gated carbon nanotube field-effect transistors with a gate length of 5 nm. Thin graphene contacts helped maintain electrostatic control. A scaling trend study revealed that, compared with silicon CMOS devices, the nanotube-based devices operated much faster and at much lower supply voltage, and they approached the limit of one electron per switching operation.

    Science, this issue p. 271

  14. Conservation Biology

    Impending primate extinction

    1. Michael Hochberg

    Emblematic primate species such as mountain gorillas are in danger of extinction. In a review, Estrada et al. report that 75% of the 504 primate species populations in the Neotropics are in decline, and 60% are threatened by extinction. This bleak outlook stems largely from anthropogenic impacts, including habitat loss, bush meat hunting, illegal trade, and climate change. Action is urgently needed because—beyond their close shared evolutionary history with humans—primates are important for numerous, underappreciated reasons, playing key roles in ecosystem dynamics, regional traditional knowledge, and economies.

    Sci. Adv. 10.1126.sciadv.1600946 (2017).

  15. Plant Signaling

    Small peptides allow rapid responses

    1. Pamela J. Hines

    RALFs (rapid alkalinization factors), a family of small peptides in plants, are produced in response to rapidly changing conditions. Stegmann et al. studied the agility and diversity built into this signaling network. Some RALFs, such as RALF23 and its relative RALF33, are activated by proteolytic cleavage. Others, such as RALF32, are not. RALF23 and RALF33 are called into play after a pathogen triggers immune responses. RALF32, on the other hand, regulates seedling growth. All three of these RALFs use the same receptor kinase, which can interact with other signaling components. Thus, plant responses can be fine-tuned by rapid release of peptides.

    Science, this issue p. 287

  16. Economics

    Using technology to beat corruption

    1. Julia Fahrenkamp-Uppenbrink

    Social safety net programs help over 1.9 billion people in developing countries such as India. But because of corruption, much of the money or goods never reach those who need them. Even low-quality rice is not safe from theft before it is distributed. In a Perspective, Hanna discusses a recent study that highlights the benefits of biometric smart cards for cash transfers in workfare and income support programs in India. The smart cards ensured that only the real beneficiaries could pick up payments, and corruption was reduced substantially. Other research shows that using technology for cash transfers particularly benefits women by giving them more control over funds.

    Science, this issue p. 244

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