This Week in Science

Science  16 Dec 2016:
Vol. 354, Issue 6318, pp. 1387
  1. Tornadoes

    Blowing harder and more often

    1. H. Jesse Smith

    Twin tornadoes over farmland in Kansas, USA

    CREDIT: CULTURA CREATIVE (RF)/ALAMY STOCK PHOTO

    The frequency of tornado outbreaks (clusters of tornadoes) and the number of extremely powerful tornado events have been increasing over nearly the past half-century in the United States. Tippett et al. found that tornado outbreaks have become more common since the 1970s. This increase seems to have been driven by consistent changes in the meteorological environment that make tornadoes more likely to form. However, the changes are not necessarily those that one would expect from climate change, which makes it difficult to predict whether this trend will continue.

    Science, this issue p. 1419

  2. Autoimmunity

    A joint effect of bacteria and genetics

    1. Yevgeniya Nusinovich

    Although rheumatoid arthritis is an autoimmune disease, scientists have long suspected that bacterial infections (and in particular, periodontal infections) may play a role in its pathogenesis. Konig et al. now demonstrate that a particular periodontal pathogen called Aggregatibacter actinomycetemcomitans (Aa) induces changes in neutrophil function. These lead to hypercitrullination of host proteins, which is also observed in the joints of patients with rheumatoid arthritis. Moreover, an association between the presence of HLADRB1 allele and increased risk of rheumatoid arthritis was only observed in patients exposed to Aa. Thus, the combination of this allele and Aa exposure could identify high-risk patients.

    Sci. Transl. Med. 8, 369ra176 (2016).

  3. Geochemistry

    Diamonds rock their metal roots

    1. Brent Grocholski

    Massive diamonds are rare, expensive, and captivating. These diamonds now appear to be distinctive not only in their size but also in their origin. Smith et al. probed mineral inclusions from these very large diamonds and found abundant slivers of iron metal surrounded by reducing gases. This suggests that the large diamonds grew from liquid metal in Earth's mantle. The inclusions also provide direct evidence of a long-suspected metal precipitation reaction that requires a more reducing mantle.

    Science, this issue p. 1403

  4. Conservation

    Too many roads

    1. Sacha Vignieri

    Roads have done much to help humanity spread across the planet and maintain global movement and trade. However, roads also damage wild areas and rapidly contribute to habitat degradation and species loss. Ibisch et al. cataloged the world's roads. Though most of the world is not covered by roads, it is fragmented by them, with only 7% of land patches created by roads being greater than 100 km2. Furthermore, environmental protection of roadless areas is insufficient, which could lead to further degradation of the world's remaining wildernesses.

    Science, this issue p. 1423

  5. Photochemistry

    Asymmetric catalysis by tuning triplets

    1. Jake Yeston

    Triplet excited states manifest a distinct mode of reactivity associated with their unpaired electrons. However, modulating this reactivity to select just one of two mirror-image products, or enantiomers, is difficult. Blum et al. found that Lewis acid coordination lowered the energy of a compound's triplet state, which allowed it to be accessed using an optically excited sensitizer. Because the Lewis acid was essential for triplet formation, it could also direct the reaction pathway toward a single enantiomer.

    Science, this issue p. 1391

  6. Induced Seismicity

    Triggered quakes get unconventional

    1. Brent Grocholski

    The big earthquakes induced by human activity are mostly linked with disposal of wastewater. However, Bao and Eaton implicate hydraulic fracturing (or fracking) as the culprit in western Canada (see the Perspective by Elsworth). Fracking near Fox Creek, Alberta, reactivated faults, clustering earthquakes along the old fault traces. Fracking does not appear to cause large earthquakes in many other areas that are prone to induced seismicity. Understanding the underlying causes of seismicity in different localities is vital for developing sound regulation to limit damaging earthquakes.

    Science, this issue p. 1406; see also p. 1380

  7. Volcanology

    Volcano monitoring goes into the deep

    1. Brent Grocholski

    Axial Seamount is a large and active submarine volcano along the Juan de Fuca midocean ridge off the coast of the western United States. Eruptions in 1998 and 2011 were followed by periods of magma recharge, making it an ideal location to include in the Ocean Observatories Initiative Cabled Array. Wilcock et al. present real-time seismic data from the most recent eruption in April 2015 that allow the tracking of magma before and during eruption. Nooner and Chadwick show that eruptions are predictable on the basis of deformation data. As magma pools underneath it, Axial Seamount inflates and erupts when the inflation hits a threshold. Both studies elucidate the dynamics of submarine volcanoes, which vastly outnumber their aboveground counterparts.

    Science, this issue p. 1395, p. 1399

  8. Plant Pathology

    Dueling for sugars

    1. Pamela J. Hines

    Bacteria thrive on sugar. So do plant cells. Yamada et al. now show how the fight for sugar plays out in the extracellular spaces around plant cells when pathogenic bacteria are invading the plant (see the Perspective by Dodds and Lagudah). In the model plant Arabidopsis, part of the defense response incited by the presence of pathogenic bacteria includes transcriptional and posttranscriptional regulation of sugar transporters. The resulting uptake of monosaccharides from the extracellular space makes life a little bit more difficult for the invading bacteria.

    Science, this issue p. 1427; see also p. 1377

  9. Ribosomes

    Getting rid of faulty mRNA

    1. Guy Riddihough

    The cell monitors the health of its mRNAs, destroying those that are faulty or damaged. Destruction by the exosome complex prevents them from being used to synthesize deranged and potentially dangerous proteins. Schmidt et al. determined the structure of the Ski helicase complex, which guides RNAs to the exosome complex destruction machinery in association with a mRNAbound ribosome. The end of the mRNA is threaded from the ribosome into the heart of the helicase, whence the message would be channeled into the maw of the exosome complex.

    Science, this issue p. 1431

  10. Antibiotic Resistance

    Defying the onslaught of antibiotics

    1. Caroline Ash

    Bacterial persistence during and after antibiotic treatment is increasingly recognized to be as challenging as the evolution of genetic resistance in the clinic. Most bacteria, including most pathogens, have an innate ability to enter dormant stages as a bet-hedging strategy to ensure survival of stress. The tactics and mechanistic details are legion. Harms et al. review the triggers and signaling involved in bacterial persistence, the important role of toxin/antitoxin modules in persistence, and how persister cells revive. On a more optimistic note, our recent understanding of the mechanisms underlying persistence opens the way to finding adjuvant drugs for antibiotics.

    Science, this issue p. 10.1126/science.aaf4268

  11. Electrocatalysis

    An activity lift for platinum

    1. Phil Szuromi

    Platinum is an excellent but expensive catalyst for the oxygen reduction reaction (ORR), which is critical for fuel cells. Alloying platinum with other metals can create shells of platinum on cores of less expensive metals, which increases its surface exposure, and compressive strain in the layer can also boost its activity (see the Perspective by Stephens et al.). Bu et al. produced nanoplates—platinum-lead cores covered with platinum shells—that were in tensile strain. These nanoplates had high and stable ORR activity, which theory suggests arises from the strain optimizing the platinum-oxygen bond strength. Li et al. optimized both the amount of surface-exposed platinum and the specific activity. They made nanowires with a nickel oxide core and a platinum shell, annealed them to the metal alloy, and then leached out the nickel to form a rough surface. The mass activity was about double the best reported values from previous studies.

    Science, this issue p. 1410, p. 1414; see also p. 1378

  12. Protein Engineering

    Engineering control of cellular proteins

    1. Valda Vinson

    The ability to switch proteins between active and inactive conformations can give insight into their function. Dagliyan et al. present a method to insert domains that control protein activity. They computationally identified protein loops that are coupled to the active site. Sensory domains inserted into these loops could modulate protein activity when their conformation was changed by light or ligand binding. The authors engineered domains into three different classes of proteins involved in cell signaling and found that switching the proteins between active and inactive states could control the shape and movement of living cells.

    Science, this issue p. 1441

  13. Structural Biology

    Rescuing stalled ribosomes

    1. Valda Vinson

    A small percentage of bacterial mRNAs lack a stop codon. Ribosomes stall at the end of such mRNAs, and the buildup of stalled ribosomes can be lethal. The primary rescue mechanism, in which translation continues on a piece of RNA that contains a stop codon, is a drug target. However, bacteria have another backup plan. James et al. present structures that show that ArfA (alternative rescue factor A) substitutes for a stop codon by binding in the ribosomal mRNA channel and recruiting RF2 (release factor 2). It mediates conformational changes required for RF2 to catalyze peptide release.

    Science, this issue p. 1437

  14. Climate Change

    The seas will rise, but by how much?

    1. Julia Fahrenkamp-Uppenbrink

    As Earth's climate warms, sea levels are projected to rise as a result of the expansion of ocean waters and melting of glaciers and ice sheets. But uncertainties over the magnitude of the rise make it difficult to develop appropriate policies. In a Perspective, Oppenheimer and Alley highlight recent studies that project higher sea levels by 2100 than the most recent assessment report of the Intergovernmental Panel on Climate Change. The main factor leading to these higher estimates is a larger projected contribution from the Antarctic ice sheet. Policy-makers would do well to develop flexible flood defense approaches that can be adapted as the scientific understanding of Antarctic ice loss evolves.

    Science, this issue p. 1375

  15. Vascular Disease

    Preventing vascular calcification

    1. Annalisa VanHook

    The arterial calcification that develops in patients with the genetic disease ACDC (arterial calcification due to deficiency of CD73) leads to peripheral ischemia. Cells from these patients have increased levels of an enzyme that degrades pyrophosphate, a compound that inhibits calcification. Jin et al. found that cells from ACDC patients had decreased pyrophosphate levels and increased activity of the mTOR pathway, which promotes calcification. These cells formed calcified teratomas when injected into mice. Teratoma calcification was reduced by treating the mice with a mTOR inhibitor or a drug that resembles pyrophosphate, suggesting new treatment options for this disease.

    Sci. Signal. 9, ra121 (2016).

  16. Structural Biology

    Structural insights into capsid flexibility

    1. Kristen L. Mueller

    Viral capsids are protein structures that enclose the genetic material of viruses. Previous structural studies of the HIV-1 capsid have relied on recombinant, cross-linked, or mutant capsid proteins. Mattei et al. now report subnanometer-resolution cryo–electron tomography structures of the HIV-1 capsid from intact virions. These structures confirm the hollow cone shape of the capsid and allow for the specific placement of each individual capsid hexamer and pentamer within the lattice structure. The structures also reveal the flexible nature of the capsid, which likely helps it to accommodate interactions with host cell factors.

    Science, this issue p. 1434