This Week in Science

Science  15 Feb 2008:
Vol. 319, Issue 5865, pp. 873
  1. Molecular Rotary Motor

    CREDIT: FURUIKE ET AL.

    F1-adenosine triphosphatase is an ATP-driven rotary motor in which a central subunit rotates inside a static cylinder. The stator provides a hydrophobic sleeve for the bottom of the rotor that could act as a bearing so that force from ATP hydrolysis can be converted to a torque. Furuike et al. (p. 955) truncated the shaft to leave just a rotor head on top of the concave rotor orifice. Surprisingly, the head rotated in the correct direction, but the average rotary speeds were low and the motion sometimes irregular. Although a fixed pivot and a rigid axle improve the efficiency of the motor, neither is required to achieve rotation.

  2. Detecting Less Massive Extrasolar Planets

    Astronomers have discovered a large number and variety of planets orbiting stars far from our solar system. Most of these detections were of bodies with masses much larger than the heaviest objects in the solar system, largely because methods for detecting them are only sensitive to massive orbiting bodies. Gaudi et al. (p. 927; see the news story by Kerr) report their observation of two planets with masses less than that of Jupiter orbiting a star of mass half that of our Sun. The discovery was made possible by an improved form of gravitational lensing in which light from distant stars is bent by the planetary system on its way to Earth.

  3. Pinning Down WIMP Detectibility

    Most of the universe is thought to be composed of dark matter, and novel ways are being sought to detect and characterize it. One strong candidate for dark matter are so-called weakly interacting massive particles (WIMPs), which interact through weak force and gravity but do not interact with electromagnetic radiation. Behnke et al. (p. 933) show that bubble chambers, which consist of superheated liquids that yield a train of bubbles from the heat produced as a particle passes through them, can be tuned to provide some limits on the abundance of WIMPs. One challenge was stabilizing the chamber for long-term measurements (most particle physics detections last for milliseconds). The cross sections measured for spin-dependent WIMP coupling do not support a recent claim of dark-matter detection.

  4. Proton Transfer Charged Ahead

    Proton transfer from hydrogen chloride to ammonia is a prototypical acid-base reaction and is known to proceed not only in solution but in dense gaseous mixtures as well. However, careful studies have shown that when isolated HCl and NH3 molecules pair up in vacuum, they form a hydrogen-bonded complex that keeps the shared proton more closely associated with chloride. Eustis et al. (p. 936; see the cover) applied photoelectron spectroscopy and theoretical simulations to explore the perturbations necessary to induce full proton transfer, and found that one driver can be the binding of an excess electron. The resulting complex is characterized as a neutral NH4 Rydberg radical species polarized by an adjacent Cl__ anion.

  5. Capturing CO2 with Organic Zeolite Analogs

    CREDIT: BANERJEE ET AL.

    Porous metal-organic framework compounds are useful for gas sorption, and a wide variety of compounds could be made, especially if different linkers between metal atoms were incorporated within the same material. However, the expectation might be that two products, each with only one of the linkers, would be favored in a mixed system. Despite this potential drawback, Banerjee et al. (p. 939; see the news story by Service) show that a combinatorial microsynthetic approach that uses Zn(II) or Co(II) centers and imidazolate and related linkers generates a large number of crystalline products with tertrahedral frameworks and zeolitic topologies. Of the 25 structures, 10 have heterolinkers and 5 have previously unobserved topologies. Three of the products show exceptional thermal stability (up to 390°C), along with high selectivity for CO2 versus CO, as well as high CO2 uptake at ambient conditions.

  6. Staying in the Fold

    A cell's proteins are continually subjected to stresses that could promote their misfolding and aggregation. In addition, a wide variety of diseases are caused by the misfolding and aggregation of key proteins. Balch et al. (p. 916) now review the so-called proteostasis machinery, which the cell uses to combat these problems. The authors highlight the potential for manipulation of the proteostasis machinery in future efforts to treat misfolding diseases.

  7. Getting a Handle on HIV Host Factors

    Because the HIV-1 virus encodes only a handful of its own proteins, it must exploit multiple host cell processes to ensure completion of its life-cycle. Thus, many potential host factors could influence HIV infection, which for the most part remain unknown. Brass et al. (p. 921, published online 10 January; see the 11 January news story by Cohen) used a genome-wide small interfering RNA functional screen to identify a large number of HIV-dependency factors, some known, but many unknown. Several of the genes were studied further and played roles in viral entry, integration, biosynthesis, and assembly, as well as in the later stages of infection.

  8. Oceans Under Threat

    CREDIT: HALPERN ET AL.

    In order to assign regional priorities to global-scale marine resource management, the type and extent of human impacts on the world's oceans must be assessed. Through quantitative, global, and high-resolution analyses of the cumulative impact of 17 of the most urgent land- and ocean-based threats to all marine ecosystems, Halpern et al. (p. 948) show that no areas of the ocean are untouched by human activities. A third of the oceans are heavily impacted, and the spatial distribution of impacts is highly heterogeneous. The most heavily affected ecosystems are continental shelves, rocky reefs, coral reefs, seagrass beds, and seamounts.

  9. Cadherins on the Road to Multicellularity

    How early organisms made the transition from unicellularity to multicellularity is unknown, although certain genes have been implicated as important players in this process. One such group is the cadherin family of genes that function in cell adhesion and cell-cell signaling. By examining the genome of the unicellular choanoflagellate Monosiga brevicollis, Abedin and King (p. 946) show that the genome of M. brevicollis contains 23 expressed cadherin genes—as many as several multicellular animals. At least two of the cadherins localized to the actin-filled microvilli of the protozoan feeding collar, where they may participate in the recognition and capture of bacterial prey.

  10. The Spider and the Grasshopper

    How do predators control ecosystem dynamics? Schmitz (p. 952; see the Perspective by Naeem) studied spiders and their grasshopper prey in a meadow ecosystem, and identified predator hunting mode and prey response as determinants of ecosystem function. Actively hunting spider species (which grasshoppers largely ignored) reduced plant species diversity and enhanced aboveground net primary production, litter quality, and nitrogen mineralization rates, whereas sit-and-wait ambush spider species (which grasshoppers avoided) had opposite effects. Top predators in marine and terrestrial ecosystems are among the fastest disappearing elements of biodiversity, and understanding their role in local ecosystem functioning may help to predict the effects of their loss.

  11. Filtering Out the Bad from the Less Bad

    Maternally inherited mitochondrial DNA (mtDNA) mutations are implicated in a variety of human diseases including cardiomyopathy and neurodegenerative disorders. It has been assumed that mtDNA mutations are randomly segregated by genetic drift within the female germline. Fan et al. (p. 958; see the Perspective by Shoubridge and Wai) created a sophisticated mouse model that allowed them to monitor the fates and phenotypic effects of mtDNAs containing mutations of varying severity. Surprisingly, the most pathogenic mtDNA mutation was quickly eliminated from the female germline, whereas a moderately deleterious mtDNA mutation continued to be transmitted through multiple generations. Thus, the female germline filters out the most deleterious mtDNA mutations prior to conception, thereby minimizing their impact on population fitness.

  12. Practice, Practice, Practice!

    Artur Rubinstein's response when asked the way to Carnegie Hall in Manhattan may in fact apply to other forms of study as well. Karpicke and Roediger (p. 966) examined undergraduates tasked with learning the meanings of 40 words in Swahili. Repeated testing of already learned words enhanced long-term recall when assessed 1 week later, whereas repeated studying had no beneficial effects. Testing required students to retrieve the English-Swahili word associations, which suggests that encoding, although critical for the formation of a memory, may not be sufficient for its retention or consolidation.

  13. Mapping Surface Phonons

    Phonons, the vibrational modes of crystals, are usually measured spectroscopically on bulk samples. Gawronski et al. (p. 930) show that phonon modes can be mapped on the close-packed (111) surfaces of gold and copper under cryogenic conditions (5 kelvin) with the scanning tunneling microscope (STM). Inelastic tunneling electronic spectra were obtained by measuring the second derivative of the tunneling current with respect to voltage, and the authors observed the expected shift in the phonon peak of 14 millielectron volts between the two metals. Changes in the phonon maps observed with atomic resolution resulted from local variations in the probability of exciting a phonon mode.

  14. Retracing Mantle Helium

    Helium isotopes provide a tracer of mantle processes. Abundant 4He is produced in the Earth from radioactive decay, whereas any 3He derives from material that was trapped during the Earth's formation. In addition, helium has been degassing throughout Earth's history. Thus, it was thought that volcanoes with low 4He/3He ratios might be tapping less degassed and more primitive layers of Earth's mantle. However, recent data showing that such volcanoes also tap regions of the mantle containing recycled ocean crust (and thus likely to be degassed) have complicated this simple picture. Albarède (p. 943, published online 17 January) proposes a solution in which helium has diffused into certain layers or parts of the mantle that have high melting points, even if they are well mixed. The distribution of volcanic emissions can be explained by different degrees of tapping of these pieces.

  15. Full Metal Abscess

    Tissue abscesses form when bacteria meet cells of the immune system, most notably neutrophils. Corbin et al. (p. 962; see the Perspective by Novick) now find that the abundant neutrophil protein, calprotectin, protects the host against bacterial growth by chelating metal ions used by the bacteria as nutrients. In mice during bacterial infection, calprotectin was localized to tissue abscesses where it chelated manganese and zinc ions. Infected mice lacking calprotectin had elevated metal levels and increased bacterial growth in tissue abscesses.

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