This Week in Science

Science  16 Jul 2010:
Vol. 329, Issue 5989, pp. 254
  1. Snapshot of a Strained Ring

    Benzene and cyclobutadiene possess diametrically opposed properties. The former, a hexagonal hydrocarbon with a geometry perfectly suited to its bonding arrangement, exhibits unusual stability. The latter, with its two fewer carbons tightly squeezed into the right angles of a 4-membered ring, rapidly forms a dimer to relieve its considerable geometric and electronic strain. Monomeric cyclobutadiene was first isolated in substantial quantity by confining it within a molecular shell, but it has eluded full structural characterization. Legrand et al. (p. 299) have now found a host lattice that stabilizes a dimethyl-substituted derivative of the molecule sufficiently to allow analysis of its structure and bonding motif by x-ray diffraction.

  2. Golden Regulator

    CREDIT: NATHAN A. MARGARVEY

    Staphylococcus aureus is a common cause of intractable infections that are exacerbated by an array of toxins and virulence factors. The agr pheromone has been thought to represent the master regulator of virulence in this pathogen, but it is not always expressed and is also found in many nonpathogenic cocci. A strictly conserved, nonribosomal peptide synthetase has now been found by Wyatt et al. (p. 294, published online 3 June) by genome mining. The enzyme assembles valine and tyrosine into cyclic dipeptides called aureusimines that are expressed by all sequenced strains of S. aureus, including the “superbug” MRSA (Methicillin-resistant Staphylococcus aureus). Microarray analysis showed a striking effect of mutation in the synthetase locus on the production of immunomodulators, hemolysins, and other exotoxins by the pathogen. Indeed, mice infected systemically with the mutant strain showed a restricted spread of infection compared with the wild type.

  3. Biocatalytic Boost

    Enzymes tend to direct reactions toward specific products much more selectively than synthetic catalysts. Unfortunately, this selectivity has evolved for cellular purposes and may not promote the sorts of reactions chemists are seeking to enhance (see the Perspective by Lutz). Siegel et al. (p. 309) now describe the design of enzymes that catalyze the bimolecular Diels-Alder reaction, a carbon-carbon bond formation reaction that is central to organic synthesis but unknown in natural metabolism. The enzymes display high stereoselectivity and substrate specificity, and an x-ray structure of the most active enzyme confirms that the structure matches the design. Savile et al. (p. 305, published online 17 June) applied a directed evolution approach to modify an existing transaminase enzyme so that it recognized a complex ketone in place of its smaller native substrate, and could tolerate the high temperature and organic cosolvent necessary to dissolve this ketone. This biocatalytic reaction improved the production efficiency of a drug that treats diabetes.

  4. Warming the Deep

    The coldest ocean waters are located at the bottoms of the major ocean basins, and, because it takes a long time for water to sink from the surface to these regions, they are relatively isolated from the warming trends that are now occurring at shallower depths. However, warming in these deep waters has recently been observed, sooner than anticipated. Masuda et al. (p. 319, published online 24 June) performed computer simulations of ocean circulation and found that internal waves are able to transport heat rapidly from the surface waters around Antarctica to the bottom of the North Pacific, which can occur within four decades, rather than the centuries that conventional mechanisms have suggested.

  5. Red Sea Coral Decline

    Large, rapid sea surface temperature rises of 1°C or greater typically cause bleaching of corals. Cantin et al. (p. 322) show that smaller temperature increases also have detrimental effects on corals, dramatically reducing their rates of calcification and skeletal extension. Corals in the Red Sea, where water temperatures have risen by 0.4 to 1°C since the mid-1970s, have declined in skeletal extension by about 30%, and decreased in calcification rates by around 18% since 1998. This finding suggests that we may see an end to coral growth in the Red Sea this century.

  6. The Greater Good

    Zero-sum games (if I win, then you lose) offer an easily grasped heuristic for all sorts of social interactions, especially those that involve money. For instance, companies may offer to contribute some portion of their revenues to charitable causes as an inducement to customers, but it is generally assumed that these pass-throughs directly diminish the corporate bottom line. Gneezy et al. (p. 325; see the Perspective by DellaVigna) have designed a framework that encourages both customers and companies to contribute toward social goods, and, in field tests, this design increased charitable contributions as well as corporate revenues.

  7. Too Close to Home?

    Why are some species common while others are exceedingly rare? Attempts to answer this question have met limited success, particularly in hyperdiverse communities, such as tropical forests. Comita et al. (p. 330, published online 24 June; see the cover) reveal a previously overlooked explanation. A large data set on seedling dynamics of 180 tree species on Barro Colorado Island, Panama, combined with Bayesian statistical techniques, revealed that species abundance is shaped by the degree to which species negatively impact their own regeneration. Rare species regenerated far less well than common species in the proximity of conspecific neighbors, suggesting a mechanism determining the relative abundances of tree species in highly diverse tropical forest communities.

  8. Hedgehog and Segmentation

    CREDIT: N. DRAY

    Segmentation is a key characteristic of body plan organization in some of the largest animal groups, including annelids, arthropods, and vertebrates, but its evolutionary origins remain debated. In arthropod embryos, the Hedgehog signaling pathway plays a crucial role in the axial patterning of developing segments. Dray et al. (p. 339) analyzed the function of this conserved pathway in the annelid worm Platynereis by using specific small molecule inhibitors and found a similar role for Hedgehog signaling in shaping segments in this animal. Thus, Hedgehog was involved in segment formation in the last common ancestor of the protostome animals, earlier in metazoan evolution than previously assumed.

  9. Gobbled by Gobies

    A common feature of overfished marine ecosystems is a tendency for biomass to become dominated by jellyfish and microbes, and for the habitat to become anoxic or hypoxic as large fish species are removed. The Benguela ecosystem off the coast of Namibia is a case in point. Utne-Palm et al. (p. 333) describe how the loss of overfished sardines from the Benguela fishery has provided an opportunity for an endemic fish species, the bearded goby, to exploit jellyfish and microbial biomass and to increase in number. These small fish have in turn become the predominant prey species for the larger fish, birds, and mammals in the region. The significance of the goby lies in its ability to forage on resources traditionally regarded as “dead-ends.” The bearded goby has thus become a key stabilizing component to the turnover of energy in the Benguela ecosystem.

  10. Wired

    CREDIT: HU AND YU

    Just as there are difficulties in making integrated circuits smaller and faster, barriers are also being reached in the fabrication of wires that connect chips to the motherboard. Hu and Yu (p. 313) describe the directed electrodeposition and bonding of copper and platinum wires via a meniscus delivered from a micropipette containing a deposition solution. Wires could be deposited on a range of substrates and were significantly smaller than those obtained using existing techniques. This approach may be useful for device packaging and might offer new approaches for constructing tailored nanoscale structures.

  11. Transcription On and sORF

    Eukaryotic transcriptomes include numerous RNAs that are presumed noncoding because they include only short open reading frames (sORFs). However, some sORF RNAs actually produce small peptides with unknown activity. Now Kondo et al. (p. 336; see the Perspective by Rosenberg) report the function of peptides containing 11 to 32 amino acids that are encoded by the gene polished-rice (pri). pri triggers N-terminal truncation of the transcription factor Shavenbaby that controls epidermal differentiation in Drosophila. Following pri expression, Shavenbaby is converted from a transcriptional repressor to an activator. Thus, sORF peptides can control transcriptional programs during embryonic development.

  12. Sulfur Signal Dinner

    Phytoplankton produces large amounts of the compound dimethylsulfoniopropionate (DMSP), which can be transformed into the gas dimethylsulfide and emitted into the atmosphere in sufficient quantities to affect cloud formation. The functional role of DMSP is somewhat unclear, but it is degraded by marine bacteria as a source of reduced carbon and sulfur. It also acts as a foraging cue for a variety of aquatic animals ranging from copepods to marine mammals. Now, Seymour et al. (p. 342) have developed a microfluidic device to observe the behavior of motile microorganisms in response to pulses of DMSP. Contrary to accepted thought, these compounds appear primarily to play a defensive role—for most motile organisms, they are strongly attractive and act as an important infochemical throughout the marine food web.

  13. Observing the Magnon Hall Effect

    The anomalous thermal Hall effect occurs when transverse heat transport is generated in the absence of an external magnetic field. The transport may be mediated by free carriers, phonons, or spin waves (magnons). Onose et al. (p. 297) observed this effect in an insulating ferromagnet and were able to rule out free carriers and phonons as the mediators of the thermal transport. Instead, the observations are consistent with a theory ascribing its origin to magnon propagation. This thermal magnon Hall effect is caused by the spin-orbit interaction, which acts in a fashion similar to the magnetic field in the conventional Hall effect. Its observation in an insulator may enable the elimination of losses in spintronic applications.

  14. Coolly Disordered

    Generally speaking, at higher temperature phases materials are more disordered—for example, when solids melt to form liquids. In some cases, however—for example, under high pressure—a more disordered phase can emerge upon cooling. Schöll et al. (p. 303) now show that an organic molecule, a naphthalene derivative, adsorbed on a silver surface disorders upon cooling below room temperature. This process is driven by the surface bond becoming stronger upon cooling and preventing weaker interactions that allow ordering between molecules in the plane.

  15. C-Family Oxidase Structure

    The heme-copper oxidases (HCOs) play a key role in aerobic respiration by coupling oxygen reduction to transmembrane proton pumping to generate electrochemical ion gradients across biological membranes that provide energy for many cellular processes. Based on subunit composition, electron donor, and heme type, the HCOs are divided into three families, of which families A and B have been structurally characterized. Buschmann et al. (p. 327, published online 24 June) now report the crystal structure of the C-family cbb3 oxidase from Pseudomonas stutzeri. The structure suggests a different redox-driven pumping mechanism from A and B HCOs, and gives insight into why C HCOs are catalytically active at low oxygen concentrations.

  16. Cenozoic Tectonics

    The Basin and Range Province of western North America—exemplified by the alternating mountain ridge and valley landscapes across nearly the entire U.S. state of Nevada—started to form ∼50 million years ago through a series of extensions of the continental crust. Prior to that, massive mountain-building collisions at the boundary between North America and the Pacific Ocean formed a subduction zone and compressed the continent. By combining observations of global subduction zone velocities with numerical modeling, Schellart et al. (p. 316) demonstrate that the thinning of the subducting portion of the oceanic plate controlled how and when the transition from compression to extension occurred. Even today, where the much smaller remnant oceanic plate continues to slowly subduct below North America in the Pacific Northwest, the width of the slab and not its age controls the velocity of subduction. Indeed, this relation may explain the dynamics of other modern subduction zones, from South America to Japan.