Editors' Choice

Science  22 Jun 2007:
Vol. 316, Issue 5832, pp. 1670
  1. ENVIRONMENTAL SCIENCE

    Fish Fatalities While Feeding

    1. Caroline Ash

    Despite the accumulated evidence that rapid climate change has deleterious effects on a broad range of animal populations, there are few data indicating how these effects are mediated. Biro et al. conducted a field experiment by stocking nine small lakes in British Columbia with trout in the warm summer of 1998 and in the cool summer of 1999. They found that water temperatures above 17.5°C increase the metabolic rate of young rainbow trout, so in order to maintain their rate of growth, the young fish compensate by feeding more actively. It became apparent that the increased feeding activity increased the young trout's visibility to predators (usually adult trout), such that the survival of the young in a warm year was only half that in a cooler year. Hence, the small increases in water temperature (of just a few degrees) caused by climate change will substantially reduce the survival of lake trout populations for which escape by migration is not possible. — CA

    Proc. Natl. Acad. Sci. U.S.A. 104, 9715 (2007).

  2. CHEMISTRY

    Droplets Hanging Around

    1. Phil Szuromi

    Microdroplets of common liquids deposited on surfaces typically evaporate in minutes if the surrounding ambient is not saturated in the corresponding vapor phase. Cheng et al. observed that microdroplets of 1-propanol and water in a 3-to-2 volume ratio showed remarkable stability when deposited on 1-decanethiolate monolayers self-assembled on gold surfaces. After initially undergoing evaporation to a volume of 0.2 μl, these microdroplets could persist for up to 5 hours. Variation of the volume ratio or deposition on substrates such as glass or polycarbonate led to rapid evaporation. The authors propose that the unusual stability results from the more volatile alcohol segregating to the bottom of the microdroplet near the hydrophobic alkyl chains, and the outer water-rich layer deriving stability from formation of a maximally hydrogen-bonded network. — PDS

    J. Phys. Chem. B 111, 10.1021/jp069063f (2007).

  3. BIOCHEMISTRY

    Bacterial Drug Design

    1. Gilbert Chin

    The most effective weapons for fighting bacterial infections are those that bacteria use against each other. One tactic for combating the spread of drug-resistant strains is to use multiple drugs, such as the combination of dalfopristin (a type A streptogramin) and quinupristin (a type B streptogramin). The former blocks an early step in ribosomal protein synthesis, whereas the latter blocks a late step.

    Korczynska et al. describe the crystal structure of virginiamycin B lyase (Vgb) in complex with quinupristin (fortuitously, a chock of dalfopristin immobilizes two Vgb molecules in the crystal, but this interaction is without an in vivo correlate). Vgb inactivates the cyclic peptide antibiotic by catalyzing a linearization, and structure-based mutagenesis supports the mechanistic proposal that ring opening occurs not via hydrolysis of an ester but by means of a C-O lyase reaction. The detailed view of quinupristin binding to Vgb is consistent with its versatility in detoxifying natural and semisynthetic type B streptogramins—the known modifications all point into the solvent and away from the active site. A comparison of this complex with that of quinupristin bound to the 50S ribosomal subunit may guide design efforts aimed at reducing its affinity for Vgb without lessening its ardor for the ribosome. — GJC

    Proc. Natl. Acad. Sci. U.S.A. 104, 10388 (2007).

  4. CLIMATE SCIENCE

    Early Reversals

    1. H. Jesse Smith

    Over the Pleistocene epoch, sea level was more than 100 m lower during some glacial periods than it is now; even within cold intervals, it may have varied by tens of meters. During the last interglacial, global average temperatures were near where they are expected to be in the coming century, and sea level was 4 to 6 m higher. Thus, conditions in that period seem relevant to our near future. Recently compiled evidence suggests that sea levels fluctuated by as much as 30 to 40 m during the beginning of that warm interval, but the large changes inferred have been controversial due to a lack of corroborating records. Andrews et al. have confirmed the variability using deposits that record the relative elevations of the Greek shoreline. By precisely determining the sample ages via U/Th dating, they found that sea level twice dropped precipitously between 136,000 and 135,000 years ago, near the end of deglaciation, an observation that supports earlier findings from the Red Sea and from Papua, New Guinea. Their results also help to constrain the timing of sea-level rise during the penultimate deglaciation. — HJS

    Earth Planet. Sci. Lett. 10.1016/j.epsl.2007.05.005 (2007).

  5. CHEMISTRY

    A Chain to Break Nitrogen

    1. Jake Yeston

    Synthetic chemists continue to puzzle over how bacteria manage the feat of reducing triply bonded nitrogen to ammonia without the help of extreme temperatures or pressures. Among the clues teased out of nitrogenase enzyme studies is the possible involvement of paramagnetic iron hydride centers. However, low-valent iron model compounds tend to be diamagnetic. Sadique et al. have applied a sterically bulky β-diketiminate ligand (L) that, despite differing structurally from the sulfur ligands in the enzyme, does coordinatively stabilize highspin Fe(II) hydrides. Moreover, like nitrogenase, the resulting model complexes can fully cleave an N=N double bond. Through a series of careful experiments, the authors explored the mechanism whereby two of these paramagnetic LFe-H centers split azobenzene (PhNNPh) to yield LFeNHPh complexes. They showed first that reaction with excess azobenzene leads to an isolable intermediate, LFeN(Ph)NHPh (shown above), which on heating is transformed into LFeNHPh and half an equivalent of azobenzene. Kinetic studies on this latter step revealed it to be first order in iron, after an induction period, which ruled out a bimolecular pericyclic rearrangement to the products. Moreover, the intermediacy of LFe-H (stemming from β-hydride elimination) was inconsistent with trapping studies. The data were most consistent with a radical chain mechanism initiated by homolytic dissociation to LFe and PhNNHPh, a hypothesis supported by disappearance of the induction period on addition of the Fe(I) complex K[LFeCl] to the reaction mixture. The results argue for deeper consideration of single-electron chemistry in probing the enzyme mechanism. — JSY

    J. Am. Chem. Soc. 129, 10.1021/ja069199r (2007).

  6. GENETICS

    Finding Bigfoot

    1. Laura M. Zahn

    The presence of conserved noncoding regions in genomes is a footprint that points to the likely existence of conserved modes of gene regulation. In plants, there appear to be fewer conserved noncoding sequences than in animals; because they are shorter, they are harder to find. Freeling et al. examined the genome of Arabidopsis, which underwent a duplication of its genome (the α event) in its recent history, in order to identify noncoding sequences that border genes and that have been retained. Large regions, relatively rich in conserved noncoding sequences (such as the G-box CACGTG), were designated Bigfoot and were often associated with transcription factor binding motifs. Smaller regions of noncoding sequences were also identified (and dubbed Smallfoot) and were often linked to components of signal transduction pathways. Few of these noncoding sequences were identified outside of paralogous genes, suggesting that the regulatory regions of other genes are less conserved or may evolve at a rapid rate. — LMZ

    Plant Cell 19, 10.1105/tpc.107.050419 (2007).

  7. STKE

    Dendrites Are Only a CLICK Away

    1. John F. Foley

    From one side of the neuronal cell body an axon emerges; from the other, a branched dendritic tree. These processes are crucial for the ability of a neuron to receive and transmit electrochemical signals via synapses. Neuronal activity is important in driving dendrite outgrowth, but the intermediary players are not well understood. Because neuronal activity increases intracellular Ca2+ concentration, roles for members of the family of Ca2+/calmodulin- dependent protein kinases (CaMKs) have been investigated. Takemoto-Kimura et al. have looked at CLICKIII (also known as CaMKIγ or CL3). They found that CL3 undergoes sequential lipid modifications of its C-terminal tail: prenylation, which anchors CL3 to the plasma membrane, followed by palmitoylation. Lipid fractionation experiments then showed that prenylated and palmitoylated CL3 was predominantly associated with lipid raft microdomains in the plasma membrane, and most of the lipid raft-localized CL3 was found in the proximal dendrites. Studies of rat embryonic neurons revealed that total dendrite length was enhanced by overexpression of wild-type but not kinase-deficient CL3, and knockdown of CL3 resulted in fewer and shorter dendrites. Lipid raft-localized CL3 in dendrites activated the Rho GTPase family member Rac, leading to rearrangement of the actin cytoskeleton of the growing dendrite. Together these data suggest that CL3 is a key factor in transducing Ca2+ transients into signals responsible for dendrite outgrowth. — JFF

    Neuron 54, 755 (2007).

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