This Week in Science

Science  30 Mar 2018:
Vol. 359, Issue 6383, pp. 1480
  1. Materials Science

    Active camouflage from a polymer

    1. Marc S. Lavine

    A new material, like chameleon skin, responds to stress.

    PHOTO: ALEX HYDE/MINDEN PICTURES

    Human skin is soft and compliant, but it can quickly become stiff when deformed to prevent injury. Chameleon skin can change color when the animal goes from a relaxed to an excited state. Although these properties can be captured individually in synthetic materials, the combination of different dynamic responses can be hard to control. Vatankhah-Varnosfaderani et al. created triblock copolymers of the ABA variety, where the A blocks have a linear structure and the B blocks are like bottlebrushes. When strained, these polymers stiffened like human skin and changed color, thus giving the materials a range of adaptive properties.

    Science, this issue p. 1509

  2. Organic Chemistry

    Attacking olefins with chiral acids

    1. Jake Yeston

    A little acid can accelerate a wide range of chemical reactions. The advent of chiral phosphoric acid derivatives has been useful for biasing these reactions toward just one of two mirror-image products. For the most part, though, these chiral catalysts have interacted with basic sites such as carbonyl groups. Tsuji et al. now extend asymmetric acid catalysis to simple carbon-carbon double bonds. Their custom imidodiphosphate forms a pocket that orients olefins to achieve mainly intramolecular alkoxylation on just one face after protonation.

    Science, this issue p. 1501

  3. Neuroscience

    Rebalancing mechanisms during sleep

    1. Peter Stern

    Synapses are often strengthened during wake periods and thus need to be homeostatically readjusted during sleep. During slow-wave sleep, synaptic depression is dominant. Sharp wave and ripple events are transient high-frequency field oscillations that occur spontaneously during slow-wave sleep in the brain. Norimoto et al. found that these events induced long-term depression of hippocampal synapses and may thus help to refine recently acquired memories (see the Perspective by Draguhn).

    Science, this issue p. 1524; see also p. 1461

  4. Cancer Immunology

    Helping NK cells find their way

    1. Priscilla N. Kelly

    MICA and MICB proteins can be expressed on tumors and act as “kill me” signals to the immune system. But tumors often disguise themselves by shedding these proteins, which prevents specialized natural killer (NK) cells from recognizing and destroying the cancer. Ferrari de Andrade et al. engineered antibodies directed against the site responsible for the proteolytic shedding of MICA and MICB (see the Perspective by Cerwenka and Lanier). The approach effectively locked MICA and MICB onto tumors so that NK cells could spot them for elimination. The antibodies exhibited preclinical efficacy in multiple tumor models, including humanized melanoma. Furthermore, the strategy reduced lung cancer metastasis after NK cell–mediated tumor lysis.

    Science, this issue p. 1537; see also p. 1460

  5. Genetics

    Genetic clines and climate change

    1. Jeremy Jackson

    Marine species exhibit strong genetic variation in relation to oceanographic conditions, but the extent to which entire assemblages of species respond in concert is unknown. Stanley et al. document genetic clines of native cod, lobster, scallop, and shrimp and an introduced crab—species that differ widely in ecology—from North Carolina, USA, to Labrador, Canada. All five species exhibit strikingly similar genetic clines, with a sharp biogeographic break between northern and southern populations centered east of Nova Scotia. The genetic break closely coincides with steep gradients in oceanographic conditions, most importantly seasonal minimum temperature.

    Sci. Adv. 10.1126/sciadv.aaq0929 (2018).

  6. Epidemiology

    The problem of pertussis

    1. Catherine A. Charneski

    The recent rise of pertussis in developed countries has generated controversy as to its cause. Domenech de Cellès et al. modeled pertussis transmission by using incidence data from Massachusetts. They found little evidence that the switch to the acellular vaccine contributed to the Massachusetts outbreaks. Instead, waning vaccine-conferred immunity, as opposed to vaccine failure to mount a full or even partial immune response, best explained the local rise in pertussis cases, along with a historical gap in vaccination coverage. Simulations suggested that administering existing boosters to children may be an effective strategy to halt pertussis transmission.

    Sci. Transl. Med. 10, eaaj1748 (2018).

  7. Applied Physics

    Shaking the small from the even smaller

    1. Marc S. Lavine

    Gently oscillate a can of mixed nuts, and eventually the larger Brazil nuts will rise to the top. Skaug et al. created three-dimensional patterned surfaces to which they applied electric fields. Combined with gentle shaking to induce a rocking Brownian motion, they were able to guide particles smaller than 100 nm along complicated paths. They could also quickly separate particles with different sizes and shapes.

    Science, this issue p. 1505

  8. Biochemistry

    ISRIB mechanism of action

    1. Stella M. Hurtley

    In rodents, a druglike small molecule named ISRIB enhances cognition and reverses cognitive deficits after traumatic brain injury. ISRIB activates a protein complex called eIF2B that is required for the synthesis of new proteins. Tsai et al. report the visualization of eIF2B bound to ISRIB at near-atomic resolution by cryo–electron microscopy. Biochemical studies revealed that ISRIB is a “molecular staple” that promotes assembly of the fully active form of eIF2B. Zyryanova et al. report similar structures together with information on the binding of ISRIB analogs and their effects on protein translation.

    Science, this issue p. eaaq0939, p. 1533

  9. Amphibian Disease

    Resistance is not futile

    1. Sacha Vignieri

    The fungal disease chytridiomycosis has wreaked havoc on amphibians worldwide. The disease is caused by the organism Batrachochytrium dendrobatidis and was first identified in the late 1990s. Voyles et al. revisited protected areas in Panama where catastrophic amphibian losses were recorded a decade ago (see the Perspective by Collins). Although disease theory predicts that epidemics should result in reduced pathogenicity, they found no evidence for such a reduction. Despite this, the amphibian community is displaying signs of recovery—including some species presumed extinct after the outbreak. Increased host resistance may be responsible for this recovery.

    Science, this issue p. 1517; see also p. 1458

  10. Nitrogen Fixation

    Sulfur steps aside for nitrogen

    1. Michael A. Funk

    Enzymatic conversion of molecular nitrogen to ammonia requires a dance of electrons and protons. The stage for that dance is the nitrogenase cofactor, a carefully constructed cluster of iron, sulfur, and carbon with homocitrate and, in some cases, bicarbonate appendages, as well as a secondary metal ion that defines the class of enzyme. The question of how this cofactor binds nitrogen has been vexingly difficult to answer. Sippel et al. report a high-resolution structure of the vanadium nitrogenase with a light atom, interpreted as nitrogen, bound to the FeV cofactor. A sulfur atom is displaced from the cofactor in this structure and is observed resting in a holding site formed by rearrangement of a glutamine residue. The putative bridging nitrogen atom suggests that diatomic nitrogen may bind to the cluster in a head-on manner, with the glutamine side chain stabilizing protonated intermediates as they are reduced.

    Science, this issue p. 1484

  11. Batteries

    Healing away the dendrites

    1. Marc S. Lavine

    The formation of lithium dendrites during charge-discharge cycles limits the development of lithium metal batteries, because the dendrites can cause electrical shorting of the cells. A number of tricks have been used to try to prevent dendrite formation. Li et al. took the opposite approach (see the Perspective by Mukhopadhyay and Jangid). They operated their cells at higher current densities, under which one would expect dendrites to form owing to the higher nucleation rates. However, under these conditions, the dendrites that started to form heated up and annealed, leading to their disappearance.

    Science, this issue p. 1513; see also p. 1463

  12. Nanomaterials

    Nanoparticle synthesis gets a shock

    1. Brent Grocholski

    Nanoparticles are useful in a wide range of applications such as catalysis, imaging, and energy storage. Yao et al. developed a method for making nanoparticles with up to eight different elements (see the Perspective by Skrabalak). The method relies on shocking metal salt–covered carbon nanofibers, followed by rapid quenching. The “carbothermal shock synthesis” can be tuned to select for nanoparticle size as well. The authors successfully created PtPdRhRuCe nanoparticles to catalyze ammonia oxidation.

    Science, this issue p. 1489; see also p. 1467

  13. Iron Homeostasis

    Iron's grip on malaria

    1. Caroline Ash

    Malaria parasites have coevolved with their human and mammalian hosts. These Plasmodium species invade the iron-rich environment of red blood cells. Zhang et al. found that the iron transporter ferroportin persists on the surface of mature mammalian red blood cells. Red blood cells are at risk of oxidative damage if their hemoglobin releases its iron; ferroportin is thus important to expel this iron. The authors also found that the transporter can deprive malaria parasites of the iron they need for proliferation. The Q248H mutation in the human ferroportin gene enhances ferroportin expression during development and seems to provide protection against malaria. This effect may explain the enrichment of the Q248H mutation among African populations.

    Science, this issue p. 1520

  14. Biophysics

    How a pathogen holds on to its host

    1. Valda Vinson

    Staphylococcus epidermidis and Staphylococcus aureus are pathogens that can form biofilms on implants and medical devices. Central to biofilm formation is a very tight interaction between microbial surface proteins called adhesins and components of the extracellular matrix of the host. Milles et al. used atomic force microscopy–based single-molecule force spectroscopy combined with steered molecular dynamics to explore how the bond between staphylococcal adhesin SdrG and its target fibrinogen peptide can withstand forces greater than 2 nanonewtons (see the Perspective by Herman-Bausier and Dufrêne). The peptide is confined in a coiled geometry in a deep and rigid pocket through hydrogen bonds between SdrG and the peptide backbone. If pulled, the load is distributed over all hydrogen bonds so that all bonds must be broken at once to break the interaction.

    Science, this issue p. 1527; see also p. 1464

  15. Viral Evolution

    Nongenetic variation drives viral evolution

    1. Laura M. Zahn

    Bacteriophage λ is a virus that infects bacteria by exploiting various membrane proteins in a well-characterized manner. Petrie et al. show how the evolution of variable folding conformations of isogenic proteins, which do not differ in their genetic sequences, contributed to λ's ability to exploit an additional host receptor for infection. Because the protein can take on two shapes, this genotype can have two phenotypes. Natural selection may thus be able to act on this nongenetic heterogeneity to connect phenotypic heterogeneity, evolvability, and protein stability.

    Science, this issue p. 1542

  16. Neuroimmunology

    Neuro-immune cell cross-talk

    1. Gemma Alderton

    An emerging mechanism of tissue homeostasis involves cross-talk between neuronal and immune cells. In a Perspective, Veiga-Fernandes and Artis discuss how neuronal and immune cells can jointly coordinate gross tissue immune responses, particularly at barrier tissues such as the intestinal and lung epithelia. They describe how neuronal cells regulate immune cells at these sites and ask whether immune cells can, in turn, regulate neuronal cells. Furthermore, the authors describe the implications of this cross-talk for diseases including chronic inflammation, cancer, and metabolic syndrome.

    Science, this issue p. 1465

  17. Cancer

    Messaging by oncogenic kinase

    1. Wei Wong

    Cancer cells signal to nontransformed cells and to other transformed cells to generate an environment that is amenable for their growth. Zhang et al. noticed that the longest isoform of the growth-promoting kinase S6K1, unlike shorter isoforms, has a six-arginine motif similar to one that enables HIV TAT protein to be released from cells and enter surrounding cells. In cultured breast cancer or nontransformed cells, adding the long S6K1 isoform to the medium enhanced the phosphorylation of S6K1 targets, as well as cell size and migration. Injection of this S6K1 isoform into mice increased the growth and metastasis of breast cancer cell xenografts.

    Sci. Signal. 11, eaao1052 (2018).

  18. Autoimmunity

    Infiltration inhibition

    1. Christiana N. Fogg

    Type 1 diabetes (T1D) is associated with the infiltration of islet-specific autoreactive cytotoxic CD8+ T cells (CTLs) into pancreatic islets. This process leads to islet destruction and loss of insulin production. Most of the CTLs in islets are non-islet-specific, and their contribution to T1D is not well understood. Christoffersson et al. observed that the accumulation of these “bystander” CTLs was associated with decreased activation and proliferation of islet-specific CTLs. The abundance of non–islet-specific CTLs in islets reduced the access of islet-specific CTLs to autoantigens, which led to a state of unresponsiveness. A similar form of nonspecific suppression by CTLs was observed in a viral meningitis model.

    Sci. Immunol. 3, eaam6533 (2018).

  19. Materials Science

    Now you see it, now you don't

    1. Marc S. Lavine

    Thermal vision cameras detect differences in temperature by sensing infrared wavelengths. If a coating could be developed that showed dynamic tuning of the effective temperature, it might be possible to hide objects from infrared sensing. Xu et al. started with a basic Bragg reflector made up of multiple layers of alternating materials with varying refractive index. The authors designed structures that were wavy to begin with so that they could be flattened out by electrical activation. This changed the infrared reflectivity and, thus, the effective temperature of the object observed in its infrared profile.

    Science, this issue p. 1495