This Week in Science

Science  27 Oct 2017:
Vol. 358, Issue 6362, pp. 493
  1. Nanomaterials

    Non–close-packed nanoparticle arrays

    1. Phil Szuromi

    Etching out one class of nanoparticles yields an open nanoarray.

    ILLUSTRATION: ELLA MARUSHCHENKO

    Films of colloidal nanoparticles usually form dense, close-packed lattices. If binary lattices could be made and one component removed, then a more open array could form, as long as the remaining nanoparticles could be stabilized. Udayabhaskararao et al. formed binary superlattices of gold and magnetite nanoparticles at an air-liquid interface that could then be transferred to carbon-coated surfaces (see the Perspective by Kotov). Selective etching of either of the nanoparticles created non–close-packed arrays with vacancies stabilized by the carbon surface.

    Science, this issue p. 514; see also p. 448

  2. Influenza

    Broadly reactive drugs for flu

    1. Caroline Ash

    Drugs for influenza are limited. For those available, viral resistance is rife. Part of the problem is that the virus is constantly mutating. Kadam et al. tested the cell entry stage of the virus life cycle as a drug target (see the Perspective by Whitehead). Cell entry is mediated by the major surface glycoprotein hemagglutinin (HA). This stage can be blocked by broadly neutralizing antibodies binding to HA. The authors generated small cyclic peptides that bind to the same sites on HA as the antibodies and mimic their activity. The peptides are cheap and easy to synthesize, are nontoxic to mice, and prevented infection of cells by many types of influenza virus.

    Science, this issue p. 496; see also p. 450

  3. Materials Science

    Combining stiffness and stretchiness

    1. Marc S. Lavine

    There is usually a trade-off between making a material stretchy, so that it can absorb energy on deformation, and making a material stiff, so that it does not extend very much when stretched. Mussels have long been an inspiration for developing adhesives that work when wet. Filippidi et al. produced an extensible polymeric material containing catechol groups whose mechanical properties were augmented when dry through the addition of iron ions (see the Perspective by Winey). The iron ions lead to sacrificial metal coordination bonds, creating a reversible load-bearing network that does not trade extensibility for stiffness.

    Science, this issue p. 502; see also p. 449

  4. Batteries

    Frozen in time

    1. Marc S. Lavine

    The electrochemical processes occurring in a battery are highly dynamic. To understand the complexities of the charge and discharge cycles, you need to be able to watch the processes in situ or to freeze the battery rapidly for ex situ analysis. Li et al. applied cryo–electron microscopy techniques commonly used for studying biological samples to examine batteries. They identified the solid electrolyte interphase that forms, observed the interactions of Li with the interphase, and captured the formation of dendrites that can be detrimental to the lifetime of a battery.

    Science, this issue p. 506

  5. Malaria

    Plasmodium parasite entrance and exit

    1. Caroline Ash

    Sweats and fever are the hallmarks of malaria. Red blood cells are the replication factories for malaria parasites. Fever occurs when the parasites' merozoite stages burst en masse from red blood cells into the circulation. Nasamu et al. and Pino et al. discovered that two parasite proteases, plasmepsin IX and X, are essential for mass cell exit (see the Perspective by Boddey). Plasmepsin X is also used by the merozoites to enter a fresh red blood cell to continue the replicative cycle. These two plasmepsins act by regulating the maturation of enzymes required to disrupt host cell membranes. Because these functions are essential for the parasite, the authors used protease inhibitors to show that plasmepsins provide potential drug targets.

    Science, this issue p. 518, p. 522; see also p. 445

  6. Pulmonary Hypertension

    Progress for PAH

    1. Caitlin Czajka

    In pulmonary arterial hypertension (PAH), pulmonary arteries are thickened and occluded, and mitochondrial respiration is suppressed. Michelakis et al. treated lungs from PAH patients with dichloroacetate (DCA), a drug that inhibits the mitochondrial enzyme pyruvate dehydrogenase kinase. DCA increased mitochondrial function, but the response was variable. This variable response was mirrored in a phase 1 trial, with some patients showing improved hemodynamics and functional capacity. Interestingly, patients with inactivating mutations in two genes encoding mitochondrial proteins were less responsive to DCA.

    Sci. Transl. Med. 9, eaao4583 (2017).

  7. Biomimetics

    Is it a bird, a plane? No, it's a robot!

    1. Rachel Kline

    This microrobot can propel itself through and between air and water.

    PHOTO: Y. CHEN ET AL./SCIENCE ROBOTICS

    Microrobots that can fly and swim need effective propulsion for both air and aquatic environments. They also need to overcome substantial surface tension when transitioning between the two. Chen et al. created a 164-mg microrobot with a gas combustion mechanism and buoyant outriggers. These design components stabilized the microrobot, overcoming the water's surface tension to allow take-off. A surfactant coating enabled diving, and a flapping-wing configuration provided functional propulsion for both air and water environments. The microrobot could land on an elastic surface, hover in air, submerge into water, and swim.

    Sci. Robot. 2, eaao5619 (2017).

  8. Cell Biology

    Elucidating a bacterial sense of touch

    1. Stella M. Hurtley

    Bacteria can adhere to surfaces within the host. This leads to tissue colonization, induction of virulence, and eventually the formation of biofilms—multicellular bacterial communities that resist antibiotics and clearance by the immune system (see the Perspective by Hughes and Berg). Hug et al. show that bacteria have a sense of touch that allows them to change their behavior rapidly when encountering surfaces. This tactile sensing makes use of the inner components of the flagellum, a rotary motor powered by proton motif force that facilitates swimming toward surfaces. Thus, the multifunctional flagellar motor is a mechanosensitive device that promotes surface adaptation. In complementary work, Ellison et al. elucidate the role of bacterial pili in a similar surface-sensing role.

    Science, this issue p. 531, p. 535; see also p. 446

  9. Membranes

    Squeezing through a hole

    1. Marc S. Lavine

    Transport of an ion is usually directly related to its hydrated radius and assumed to be nonflexible. Either a hydrated ion fits through an aperture or it does not, and shape should play a dominant role rather than charge. Esfandiar et al. created nanofluidic devices by stacking structured bulk materials, including graphite, boron nitride, and molybdenum disulfide. They investigated the transport of ions in aqueous solutions through the nanochannels in the devices. Unexpectedly, they observed different behavior for ions of similar hydrated size but opposite charge.

    Science, this issue p. 511

  10. Microbiology

    Bacterial toxin acetylates lysine residues

    1. L. Bryan Ray

    A toxin produced by the bacterium that causes cholera has a catalytic activity that contributes to its effects on the cytoskeleton of host cells. Zhou et al. determined the protein structure of the Rho guanosine triphosphatase (GTPase)–inactivation domain of the toxin from Vibrio cholerae and found it to be similar to that of a human fatty acyltransferase. Indeed, the toxin peptide could catalyze fatty acylation of lysine residues of Rho-family GTPases, which regulate the actin cytoskeleton. Such covalent modification of lysine residues in mammalian proteins had been noted before, but the enzymes responsible were not known.

    Science, this issue p. 528

  11. Infrastructure

    Building the right roads in the right places

    1. Julia Fahrenkamp-Uppenbrink

    The current boom in global infrastructure development is likely to include the construction of millions of kilometers of new roads, particularly in tropical and subtropical regions. In a Perspective, Laurance and Burgués Arrea argue that road planning often overestimates socioeconomic benefits and does not adequately account for road maintenance costs, while also threatening ecosystems and the services that they provide. A proactive planning approach can help to bridge opposing views and guide construction of roads in the right places for the benefit of human society and the natural environment alike.

    Science, this issue p. 442

  12. Cancer

    The good side of ceramides

    1. Leslie K. Ferrarelli

    Tumor growth is enhanced by some members of the ceramide family of lipids and the enzymes that produce them. However, Gencer et al. found that C18-20 ceramides synthesized by the enzyme CerS4 acted as tumor suppressors. The ceramides prevented a transforming growth factor–β (TGF-β) receptor complex from activating the Shh pathway. CerS4 inhibited metastases from mammary tumors and the development of the hairloss disorder alopecia in mice. The TGF-β and Shh pathways are challenging to target pharmacologically; these findings suggest that some ceramides may have therapeutic potential against these pathways in various disorders.

    Sci. Signal. 10, eaam7464 (2017).

  13. Imaging

    An ultrasound bioprobe for biological imaging

    1. Warren Warren

    Biological imaging past the diffraction limit has provided important tools for understanding the chemistry of life. Shekhawat et al. developed a method to detect the phase of scattered ultrasound waves for high-resolution imaging of biological systems in liquid media. They successfully imaged magnetic cores in silica core shell nanostructures and were able to determine localized stiffness of intracellular fibers in thrombin-stimulated endothelial cells. This approach opens applications in biomedical and molecular imaging with subsurface resolution down to the nanometer scale.

    Sci. Adv. 10.1126/sciadv.1701176 (2017).