Editors' Choice

Science  01 Oct 2010:
Vol. 330, Issue 6000, pp. 12
  1. Chemistry

    Breaking Methanol

    1. Jake Yeston

    Titanium dioxide (TiO2) is a highly abundant material, and as such has been heavily investigated for widespread use of its photocatalytic properties. One potential application of increasing importance is the direct use of sunlight to generate hydrogen from water, a reaction that proceeds more readily at TiO2 surfaces when some methanol is mixed in. In this context, Zhou et al. have explored the behavior of methanol monolayers and submonolayers on TiO2 under ultraviolet irradiation. Using both two-photon photoemission spectroscopy and scanning tunneling microscopy, the authors present evidence for photoinduced dissociation of the adsorbed methanol via H transfer from the CH3O-H bond to a bridge-bonded oxygen on the TiO2 surface. Accompanying density functional calculations support assignment of the photoemission signal to perturbation of Ti d-orbitals by virtue of the tetravalent metal ion's interaction with the CH3O radical co-product, which pushes the ion out of plane. The temporal profile of the emission was not mono-exponential, implicating heterogeneous kinetics.

    Chem. Sci. 1, 10.1039/c0sc00316f (2010).

  2. Biochemistry

    Flexible Exchange Rates

    1. Gilbert Chin
    CREDIT: WATT ET AL., PROC. NATL. ACAD. SCI. U.S.A. 107, 16823 (2010)

    The membrane-bound enzyme F-ATPase serves an important function in almost all walks of life. It makes ATP (from ADP and inorganic phosphate) by converting the passage of protons down an electrochemical gradient first into mechanical energy and thence into chemical energy. The parts of the enzyme (red and yellow) that bind ADP lie mostly outside the membrane, and three such binding sites are converted sequentially from open to loose to tight conformations. The energy contained in the movement of protons is extracted by forcing them through a membrane-embedded ring (brown) of identical subunits, each of which captures a single proton on a glutamate residue. Turning this ring rotates a central stalk (blue, purple, and green) at 6000 rpm, which drives the cycle of conformational changes. Watt et al. describe the crystal structure of the mitochondrial ring and show that it contains eight subunits, leading to a ratio of eight protons for three ATPs synthesized. What is puzzling is the range of stoichiometries documented thus far, with 10 to 15 subunits found in the F-ATPases of fungi, bacteria, and chloroplasts. All of these enzymes possess the canonical trio of ADP-binding sites, which means that the cost of each ATP varies from as little as 2.7 protons in animals to as many as 5in microbes.

    Proc. Natl. Acad. Sci. U.S.A. 107, 16823 (2010).

  3. Genetics

    Not a Dog's Breakfast After All

    1. Sacha Vignieri

    Dogs have been our companions for thousands of years. This long allegiance and our preferences for dogs with certain traits have led to an unmatched degree of morphological variation and an opportunity for geneticists to unravel how genes interact with selection to shape phenotypes. Recent work in this area has revealed much about the genes underlying specific traits, such as coat color, foreshortened limbs, and hairlessness. Boyko et al. have examined variation at over 60,000 single-nucleotide polymorphisms in 80 dog breeds, African village dogs, and wolves. Interestingly, they found that the majority of variation among breeds was generated by just a few genomic regions of large effect. For example, they identified only six regions associated with body size, and ear floppiness was associated with just a single region. They hypothesize that the small number of regions controlling such a large degree of variation is probably due to the repeated bottlenecks dogs went through in their evolution, first when they were domesticated and then during breed development. Genetic diversity measures support this hypothesis, as all breeds displayed much lower genetic diversity than either wolves or village dogs.

    PLoS Biol. 8, e1000451 (2010).

  4. Ecology

    'Round Midnight

    1. Laura M. Zahn

    Bird in the spotlight.

    CREDIT: ©AF ARCHIVE/ALAMY

    Increasingly, artificial light sources are found on the edges of urban areas, and Kempenaers et al. have investigated the effect of nighttime illumination on bird behavior and reproduction. From a 7-year study of the reproductive behavior of blue tits, they found that female birds laid eggs on average 1.5 days earlier when living in regions exposed to artificial lighting and that this effect was strongest in the birds nearest to the light sources. In addition, males started singing earlier in the pre-dawn hours, especially if they were younger, and males in lighted territories were more successful at extra-pair matings. The full human impact on the behavioral ecology of these blue tits is not known, but the authors conclude that it may result in differential selection for indicators of good genes among populations whose effects cannot yet be determined.

    Curr. Biol. 20, 10.1016/j.cub.2010.08.028 (2010).

  5. Molecular Biology

    Getting Involved Locally

    1. Helen Pickersgill

    MicroRNAs (miRNAs) are small RNAs of around 22 nucleotides that bind to protein-coding messenger RNAs (mRNAs). They regulate function in diverse cellular processes, particularly during development and also in cancer. Understanding how miRNAs themselves are regulated is an emerging area of interest. The cyclin-dependent kinase inhibitor p27 negatively regulates the G1 to S phase transition of the cell cycle. Translation of p27 mRNA is inhibited in many cancer cell types by two miRNAs, miR-221 and miR-222. However, p27 accumulates in nondividing (quiescent) cells, despite the presence of high levels of miR-221 and miR-222, suggesting an additional level of regulation. Kedde et al. have discovered that the ability of these miRNAs to inhibit p27 is regulated by another RNA binding protein, Pumilio-1. The binding site of Pumilio-1 in the 3' untranslated region of p27 is located close to the binding sites for miR-221 and miR-222. The authors found that Pumilio-1 binding could reconfigure the local RNA structure, thereby granting the two miRNAs access. They propose that entry into the cell cycle of quiescent cells involves phosphorylation of Pumilio 1, which stimulates its binding to p27 mRNA, thereby exposing the nearby miRNA binding sites. These results suggest that specific binding proteins can structurally remodel RNAs, like they do chromatin, in order to regulate function.

    Nat. Cell Biol. 12, 10.1038/ncb2105 (2010).

  6. Astronomy

    Milky, Not Dusty

    1. Maria Cruz

    As many of us now learn at a young age, our solar system hosts small planets close to the Sun and giant planets farther out. What do the first planetary systems that formed in our Galaxy look like? Sheehan et al. used the Spitzer Space Telescope to search for dust around stars that formed early in the Milky Way's history. The stars they observed are twice the age of our Sun. Detection of discs of dust and debris around these stars would be a sign that at least small planetary bodies formed around them, because these discs are generated and maintained through collisions between comets and asteroids. Of the total of 11 stars observed by the authors and 11 others observed by other groups, none showed signs of dust. This does not necessarily imply that these stars do not host planetary systems; some of them are known to be orbited by giant planets. The lack of dust implies that some of these systems did not stop at planetesimal growth but proceeded to giant planet formation. They could be analogues of our solar system, where there is very little cometary dust left after the formation and evolution of the gas giant planets.

    Mon. Not. R. Astron. Soc. 10.1111/j.1745-3933.2010.00936.x (2010).

  7. Applied Physics

    Calling for a Quantum Hush

    1. Ian S. Osborne

    Too loud out there?

    CREDIT: ISTOCKPHOTO.COM

    Coupling the mechanical and optical degrees of freedom of a system, in for example an atomic force microscope, provides the ability to measure displacements on exquisitely small length scales and to image surface height variations of just a single atom. As the systems are designed with better sensitivity (as required for the potential detection of gravity waves in large interferometers) noise can become an increasingly dominant issue. This noise can arise from back-action, whereby the radiation pressure caused by the probe light can perturb the motion of the mechanical system. Optomechanical systems are now entering a sensitivity regime where the light and mechanical motion can be described quantum-mechanically. In analogy to the operation of noise reduction headphones, which record the ambient noise and then play it back with the amplitude negated to prompt destructive interference, Tsang and Caves propose a route to develop quantum noise cancellation for applications in optomechanical sensor systems. They break the problem down into a number of components and in a flowchart representation deal with each component separately, introducing an anti-noise path. In their admittedly idealized system they show how such an approach can deal with the back-action noise and should lead ultimately to improved sensors.

    Phys. Rev. Lett. 105, 123601 (2010).

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