This Week in Science

Science  27 May 2011:
Vol. 332, Issue 6033, pp. 1005
  1. All Wrapped Up


    Proteins can be used to bind selectively to specific surfaces, but can proteins be designed to form a superstructure on the bound surface? Grigoryan et al. (p. 1071) describe an algorithm for generating specific protein sequences that would allow for the wrapping of carbon nanotubes with specific helicities. The design was accomplished by first parameterizing the geometry of the nanotube wrappings and then matching the geometry to known protein backbones. Then a combination of chemical intuition, conservation, and computational design was used to determine the peptide sequences. The designs were verified by a variety of biophysical measurements, including a crystal structure of a peptide dimer (without the nanotube) and 2D photoluminescence of suspended nanotubes stabilized by the peptides.

  2. Understanding Dyscalculia

    For some people, understanding mathematics comes so easily that it seems as if the world is written in numbers. For those with dyscalculia, a disorder that reflects impaired math skills, all the effort and studying possible still leaves math a mystery. The effects of dyscalculia echo through a person's life, lessening school progress and employment opportunities. Butterworth et al. (p. 1049) review what is known about dyscalculia, what genetic and developmental factors may contribute to the disorder, and what sorts of educational interventions may help.

  3. Baby Einsteins

    Having complete information with which to make predictions is a rarity and is often achieved only in theoretical studies with paper and pencil. Téglás et al. (p. 1054) now find that when 12-month-old infants view complex displays of multiple moving objects, they can form rational probabilistic expectations about future events by integrating dynamic spatiotemporal cues present in a scene, weighting these information sources as predicted by a Bayesian ideal observer model.

  4. Repeated Corrections

    Quantum computation involves having to work with fragile quantum states that have a tendency to decay on a rather short time scale. While techniques abound for mitigating the losses and improving the robustness of the systems, errors are unavoidable and so quantum error correction algorithms will be required for the implementation of large-scale quantum systems. Schindler et al. (p. 1059) describe a multiple correction algorithm applied to a three-qubit (3 atoms) system where the loss of information encoded on the atoms is protected against. Multiple correction algorithms are likely to become a necessary component for scaling up to practical systems.

  5. Binary Logic on an Island

    Scanning tunneling microscopes with magnetic tips have enabled precise manipulation and spin readout of surface-adsorbed atoms. By placing atoms at just the right distance from each other, it is possible to control their spin states based on the distance-dependent Ruderman-Kittel-Kasuya-Yosida interaction, making these systems an attractive candidate for spin-based computation. Khajetoorians et al. (p. 1062, published online 5 May; see the Perspective by Heinrich and Loth) now describe a device consisting of two atomic spin chains, each attached to a magnetic island whose magnetizations can be manipulated independently. An output atom placed in the vicinity of the ends of the two spin chains was able to perform a binary logic OR operation with the help of an external magnetic field.

  6. Electrically Switched Magnetism

    Magnetic memory is a robust, cheap, and widely used medium for information storage. Controlling the magnetic behavior with an electric field would provide further functionality and lower power consumption of devices. While such control has been demonstrated in dilute magnetic semiconducting materials, it has been limited to very-low-temperature operation. Using an electrolyte double-layer gate structure, Yamada et al. (p. 1065; see the Perspective by Žutić and Cernĕ) were able to modulate the carrier density and the magnetic properties of cobalt doped TiO2 at room temperature. The findings should help in the development of practical spintronic devices.

  7. Hawaii's Deep Plume—Ponded


    Hotspots in Earth's crust are often considered to be the products of vertical plumes of hot material upwelling from great depths to form surface structures. The Hawaiian islands are perhaps the most commonly cited example, but efforts to image a plume using a range of seismological techniques have provided often contradictory results. Another method is to look at the temperature-dependent depth of mineral phase transitions—which result in seismic discontinuities—throughout the region where a plume purportedly exists. Cao et al. (p. 1068) interpreted inverse scattering of SS waves to create a topographic view of these discontinuities beneath near Hawaii. Instead of a narrow vertical structure, the results show a broad thermal anomaly west of the islands at the depth of one of the seismic discontinuities. Hotspot volcanism in Hawaii may thus be derived from a deep pond of hot material that gets carried by the flowing mantle up to the surface.

  8. The Ocean's Layers

    A long interval of continental-scale Antarctic glaciation began about 34 million years ago at the beginning of the Oligocene, after 25 million years of global cooling following the peak warmth of the early Eocene, an event that had great influence on global climate and ecosystems. Katz et al. (p. 1076) compared the carbon- and oxygen-isotopic compositions of benthic foraminifera from shallower waters from the western North Atlantic continental slope and those of the deep Southern Ocean. The findings revealed a large difference between water masses developed in the early Oligocene, probably as the result of the development of Antarctic Intermediate Water. At the same time, the densest water, formed around Antarctica, was confined by a strengthening Antarctic Circumpolar Current to higher latitudes, forming a bottom layer generating a four-layered ocean like the one that exists today.

  9. Predicting Ecosystem Change

    Rapid transitions, or phase shifts, have been observed in diverse types of ecosystem, and often result from the loss or addition of top predators. Carpenter et al. (p. 1079, published online 28 April) show that it can be possible to detect an impending phase shift before it actually occurs. The populations of large predator fish in a northern American lake ecosystem were manipulated, and the effects of population change on other components of the food web were compared with an adjacent control lake. Subtle, but distinct, changes were observed in the manipulated lake at least a year before the transition of the food web to a new structure occurred.

  10. Plasticity in Limb Development


    The development of limbs has long been a model for understanding vertebrate development. As the buds grow, the different parts of the limb proximal-distal (PD) axis are laid down from the shoulders to digit tips in a temporal sequence. Prior work has invoked a clock-like mechanism, one that is insensitive to instructive signals. Two papers now provide an alternate view of PD patterning (see the Perspective by Mackem and Lewandoski). Cooper et al. (p. 1083) grew chick limb mesenchyme in tissue culture conditions where the signaling environment could be controlled and then grafted the cells onto the flank of a chick embryo, where they formed recognizable limb structures. The findings suggest that the set of signals seen by the early limb bud both keep the mesenchyme undifferentiated and also maintain its potential to form all three major limb segments. As the limb bud grows, PD regionalization results from the balance between proximal and distal signals. Roselló-Díez et al. (p. 1086) reach a similar conclusion, transplanting recombinant and normal chicken limb buds to host embryos.

  11. Hostile Takeover

    One of the hallmarks of the host's response to viral infection is the production of interferon cytokines, which trigger the induction of a broad array of antiviral genes. Viperin is an interferon-inducible gene whose expression is induced in response to infection with human cytomegalovirus (HCMV). Seo et al. (p. 1093, published online 28 April) now show that HCMV co-opts viperin to its advantage. vMIA, a virus-encoded protein, interacted with viperin and induced viperin relocalization from the endoplasmic reticulum to the mitochondria in response to infection. Mitochondria-localized viperin inhibited ATP generation in the mitochondria, which resulted in disruption of the actin cytoskeleton and enhanced viral replication.

  12. Microbes Beat Disease

    Most soil communities limit plant-pathogen activity to some degree by virtue of competition by resident microorganisms. But some naturally occurring soils develop an ability to suppress specific pathogens, often after a disease outbreak, suggesting that a specific microbial community has been selected. Mendes et al. (p. 1097, published online 5 May) investigated a soil that had developed resistance to the widespread fungal pathogen and saprophyte, Rhizoctonia solani. Strains of pseudomonad bacteria were isolated from the suppressive soil that were most efficient at inhibiting the pathogen in bioassays. Subsequent mutagenesis and functional studies revealed these bacteria were using nonribosomal peptide synthestase to synthesize an antifungal chlorinated lipopeptide resembling syringomycin.

  13. Son of SAM

    The radical SAM enzymes RlmN and Cfr catalyze methylation of bacterial ribosomal RNA, modifying positions in the aromatic rings of adenosine that are not inherently reactive. Recently, it was shown that the reaction occurs in two steps. First, a cysteine in the enzyme is methylated by standard SAM chemistry. A second SAM molecule is reductively cleaved, abstracts a proton from the methylcysteine, and the resulting methyl radical transfers to the adenine base. Boal et al. (p. 1089, published online 28 April) report a high-resolution structure of RlmN with SAM bound, which has a methylated cysteine. The structure reveals how the structure accommodates the unusual mechanism and shows that both standard SAM methyl donation and reductive cleavage of SAM are achieved using a single binding site.

  14. Pressure to Conform

    Surveys of cultural groups around the world have provided evidence of variation in social beliefs (for example, collectivistic versus individualistic) and behaviors (for example, attendance at religious services). Gelfand et al. (p. 1100; see the Perspective by Norenzayan) constructed a social dimension of measurement that they term tightness—looseness, or the extent to which societies impose social norms. Reports were collected from almost 7000 individuals distributed across 33 large-scale cultures, and the data set was used to characterize how cultures shift along this dimension in response to ecological and societal challenges.

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