Editors' Choice

Science  05 Jun 2009:
Vol. 324, Issue 5932, pp. 1242
  1. Geology

    How Heat Stirs the Mantle

    1. Brooks Hanson

    In the aftermath of earthquakes, seismic tomography offers a window into mantle dynamics through large-scale inversion of recorded seismic velocities along different paths. Observed variations in velocity generally reflect mantle density, but the patterns could also indicate shifts in temperature, composition, grain size, or water content. To address this conundrum, Dalton et al. conducted a global inversion of seismic attenuation, which responds differently to variations in these parameters than does the shear-wave velocity. The data (constrained further by recent laboratory studies of the mineral olivine, abundant in the upper mantle) imply that temperature variations of about 150° to 200°C can explain most of the patterns beneath ocean basins in the upper mantle but that a different composition must be invoked beneath continents at depths less than 250 km. In a complementary approach, Schuberth et al. focused on the lower mantle, comparing seismic data with a numerical mantle circulation model. They also found that much of the observed seismic data, including an apparent large upwelling beneath Africa, can be well accounted for by temperature variations alone (of up to 1000°C) produced by high heat flow from the core.

    Earth Planet. Sci. Lett. 10.1016/j.epsl.2009.04.009 (2009); Geochem. Geophys. Geosyst. 10, 10.1029/2009GC002401 (2009).

  2. Materials Science

    A Basic Deposit

    1. Phil Szuromi
    CREDIT: LIU ET AL., ADV. FUNCT. MATER. 19, 1015 (2009)

    Manganese dioxide (MnO2) meets many of the requirements as an electrode in lithium (Li) batteries, but the bulk material exhibits low capacity and poor cycling because Li ion intercalation distorts the crystal lattice. Nanostructuring of the bulk material can alleviate some of the problems, but typical templating routes for creating mesoporous MnO2 have not been cost-effective. Liu et al. report on the deposition of mesoporous MnO2 films through a two-step cathodic deposition process driven by water electrolysis. Hydroxide ions generated at the cathode in a 0.1 M Mn2+ solution formed Mn(OH)2, which precipitated, and after exposure to air, formed MnO2·0.5 H2O. This material has a nanowall-array morphology (shown at left) with high surface area (96 m2 g−1) and an energy storage capacity with Li ions of 256 mA·hour g−1. The higher capacity and better cycle life of this material, relative to the material formed directly in an anodic version of the process (80 mA·hour g−1), were attributed to the mesoporous structure of the nanowalls.

    Adv. Funct. Mater. 19, 1015 (2009).

  3. Behavior

    Intervening to Reduce Risk

    1. Barbara R. Jasny

    There have been many discussions of how genes and environment might interact in the context of human behavior. Brody et al. have studied the effects of a randomized behavioral intervention on adolescents who have a genetic polymorphism associated with the initiation of risky behavior. Roughly 600 11-year-olds were randomly assigned to the Strong African American Families (SAAF) program or to a control group. The SAAF group (and their caregivers, usually mothers) participated in separate and joint training sessions on parenting practices, stress management, dealing with racism, setting goals, and norms for the use of alcohol and other substances. Sessions occurred over the course of 1 year, and the initiation of risky behaviors was assessed at the beginning of the program and for the next 2.5 years. Two years later, saliva samples were collected to look for a polymorphism in the promoter region of the serotonin transporter. Possession of a short form of the allele has been associated previously with impulsivity, substance abuse, and early sexual activity. In the control group, adolescents with the short allele were twice as likely to have engaged in risky behaviors as those assigned to the SAAF group or those with the long allele in either group. Only one genetic polymorphism was examined, and the results need to be confirmed in a variety of populations; however, this provides further evidence of the value of this intervention and the mutability of the effects of genetic predisposition.

    Child Devel. 80, 645 (2009).

  4. Immunology

    Vascular Nets

    1. Lisa D. Chong
    CREDIT: KESSENBROCK ET AL., NAT. MED. 15, 10.1038/NM.1959 (2009)

    During an infection, invading microbes can be caught in sticky webs of chromatin (DNA + histones) that are released by neutrophils. These neutrophil extracellular traps are decorated with granules that are laden with lytic enzymes and antimicrobial peptides; these weapons facilitate the rapid killing of pathogens.

    In small-vessel vasculitis (SVV), the body generates antibodies against two antigenic proteins that are expressed by neutrophils, and this leads to the inflammation of small blood vessels. How this chronic condition is sustained has not been clear, but Kessenbrock et al. have found that these nets are also produced in the absence of infection and that they may perpetuate autoimmune disorders. It appears that when neutrophils are attacked by these autoantibodies, they release their fibrous chromatin nets (shown above), which contain the two antigens. Kidney biopsies from patients with SVV confirmed the presence of neutrophils and nets near deteriorating capillaries. This immune response probably maintains the exposure of the autoantigens to other immune cells (dendritic and B cells), whose consequent activation could play a pathogenic role in the disease.

    Nat. Med. 15, 10.1038/nm.1959 (2009).

  5. Biochemistry

    Stuck in the On Position

    1. Gilbert Chin

    Protein kinases are of course central components of many signaling pathways in cells. Cascades of kinases, in which the first kinase in a series modifies the second and enhances its enzyme activity, are not uncommon, and BRAF sits in a pathway that begins with a membrane-bound receptor tyrosine kinase and ends with the movement of the extracellular signal-regulated kinase into the nucleus. The special interest in BRAF arises from the frequent association of a mutation (V600E) of a valine to a glutamate with malignant melanoma. Xie et al. describe kinetic and structural studies of the interaction of wild-type and mutated forms of BRAF with kinase inhibitors built on a ruthenium (fuschia above) half-sandwich scaffold. They provide a structure-based explanation for the higher potency of one such inhibitor (CS292) for the V600E mutant versus the wild-type enzyme and use this information to design a more specific and more potent derivative. They also explain how the substitution of a glutamate electrostatically mimics the normal, activating phosphorylation of nearby serine and threonine residues, but with the critical distinction that activation in the BRAF mutant is irreversible.

    CREDIT: JIE QIN

    Biochemistry 48, 10.1021/bi802067u (2009).

  6. Chemistry

    Microscopic Window Washing

    1. Marc S. Lavine

    High-resolution imaging of organic polymers in a transmission electron microscope (TEM) is hampered by the accumulating residue of electron beam–induced sample decomposition. Horiuchi et al. solve this problem through gentle cleaning of their microscope with oxygen radicals generated in a low-temperature plasma near one of the accessory ports. An extra pumping system added at the objective aperture pulled the oxygen radicals into the sample chamber. The authors used their TEM to examine brushes of a phosphorylcholine that had been grafted onto silicon nanoparticles via a surface initiator. Once oxidation (and hence volatilization) of the residue cleared the field, they could see the brushes extending from a nanoparticle, and even visualize the intermingling of brushes in two neighboring particles. Mapping of the intensity profiles distinguished the initiator, with a high carbon density near the particles and the broader brushes where the carbon density was lower.

    ACS Nano 3, 1297 (2009).

  7. Cell Biology

    Wrestling with Heat Shock

    1. L. Bryan Ray

    Golebiowski et al. have conducted a comprehensive large-scale analysis of protein SUMOylation. Small ubiquitin-like modifier (SUMO) proteins, when covalently attached to target proteins, can alter properties such as the cellular localization, activity, or stability of the targets. By combining an affinity-tagging isolation method with sensitive mass spectrometry detection, the authors obtained a glimpse of 766 proteins that experienced increased or decreased SUMOylation in cells exposed to the stress of heat shock (a temperature increase from 37° to 43°C). Three-quarters of these proteins had not been identified previously as targets of SUMOylation. These proteins provide clues to the extent of the biological processes that are altered by heat shock—from DNA repair and protein folding to cell death and cell cycle control. Furthermore, this regulatory mechanism operates quickly, within 5 min, although reversal of SUMOylation was generally slower, taking up to 2 hours—and for those proteins that underwent deconjugation in response to stress, an even longer recovery time was needed for re-SUMOylation.

    Sci. Signal. 2, ra24 (2009).

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