Editors' Choice

Science  12 Sep 2008:
Vol. 321, Issue 5895, pp. 1419

    Redshift Resolution

    Dyes operate by absorbing specific wavelengths of light, thereby changing the overall color we perceive in looking at a dyed liquid or solid. In general, though, the color a dye confers depends not only on its molecular structure but on the medium in which it's been dissolved or suspended. Renger et al. derive a remarkably simple relation for predicting how the electronic absorption spectrum of an isolated nonpolar dye molecule will shift upon dissolution in a nonpolar solvent. In contrast to polar media, the influence of the weaker and more rapidly varying charge distributions in nonpolar media has remained puzzling. A prevailing model derived more than 50 years ago suggested that the absorption spectrum should shift to longer (redder) wavelengths as the strength of the absorption increased. However, the authors show that instead, the shift scales with the energy of the state accessed by the light absorption. They support their relation by accurately predicting spectral shifts for the bacteriochlorophyll a and bacteriopheophytin a chromophores. — JSY

    Proc. Natl. Acad. Sci. U.S.A. 105, 13235 (2008).


    Folding Proteins

    In many patients who suffer from loss-of-function genetic diseases, the missing protein is translated, but a point mutation causes misfolding and subsequent degradation of the protein. Pharmacologic chaperones, which help to restore function by binding to and stabilizing successfully folded proteins, have shown some therapeutic promise, but are inherently disease-specific. A more general strategy to encourage proper folding would be to enhance cellular protein homeostasis mechanisms, including the unfolded protein response (UPR) and the heat-shock response (HSR). Mu et al. have identified two small molecules, celastrol and the proteasome inhibitor MG-132, that each increase mutant protein folding and activity in patient-derived cell lines from two different lysosomal storage diseases, Gaucher and Tay-Sachs. These compounds up-regulate multiple UPR and HSR components, and two UPR proteins of the endoplasmic reticulum (IRE1 and PERK) are required to mediate the beneficial effects in both cell lines. Coapplication of these drugs with known pharmacological chaperones had a synergistic effect and increased the activity of the mutant proteins to at least 50% of wild-type activity. These results provide a proof-of-principle milestone in the therapeutic approach of developing protein homeostasis regulators to treat a range of loss-of-function diseases. — NM*

    cell 134, 10.1016/j.cell.2008.06.037 (2008).

    • * Nilah Monnier is a summer intern in Science's editorial department.


    Have Your Plants and Eat Them, Too

    An experimental study of Arctic vegetation shows that herbivores can exert a strong influence on the ecological outcomes of climate warming in plant communities. Numerous studies have shown that warming leads to changes in the biomass, structure, and composition of plant communities. In Arctic tundra in particular, warming leads to increases in aboveground plant biomass and of shrubby vegetation at the expense of grasses. Post and Pedersen conducted a 5-year experiment in which large vertebrate herbivores (musk ox and caribou) were either excluded from or allowed access to artificially warmed or ambient temperature exclosures. The warmed plots from which the herbivores had been excluded showed the expected transition to higher biomass and domination by woody plants (dwarf birch and willow). However, the plant communities on the grazed warmed plots were indistinguishable from those on the ungrazed ambient plots after 5 years. These results suggest that large herbivores might be useful in mitigating the effects of climate change in tundra—and perhaps in other rangeland habitats. — AMS

    Proc. Natl. Acad. Sci. U.S.A. 105, 12353 (2008).


    An Umbrella or a Sieve?

    Modern fabrication techniques can not only produce materials that show strong wetting or repulsion of water or organic liquids, but also offer dynamic control of the wetting behavior in certain cases. Lifton et al. fabricated a silicon membrane with honeycomb-shaped pores, overcoated with a nanonail architecture and an organic self-assembled monolayer or fluoropolymer. Under normal conditions, the membrane repels droplets of water or organic liquids, but after application of a voltage pulse, the droplets undergo an electrowetting transition and the fluid seeps into the pores. For a water droplet, to ensure that the fluid passed through the membrane, the authors placed a hydrophilic glass fiber filter underneath the membrane. They further fabricated a battery in which the tunable membrane keeps the liquid electrolyte and solid electrode separate until a voltage pulse is applied. Because there is no liquid penetration during storage, no electrochemical reactions occur, and so this sort of battery should have an extremely long shelf life. — MSL

    Appl. Phys. Lett. 93, 43112 (2008).


    In Capsule Form

    Intracellular membrane-bounded compartments—the mitochondrion, chloroplast, and nucleus—define the modern eukaryote. Bacteria make do without internal membranes, yet it is becoming evident that they do possess, nevertheless, intracellular nanosized environments. Sutter et al. describe the structure of the latest such oasis—an icosahedral shell 25 nm in diameter, formed by 60 monomers of the protein encapsulin. As one might intuit, encapsulin is structurally similar to viral capsid proteins, although any ancestral commonalities are no longer visible in their amino acid sequences. Compartments can be useful for sequestering small molecules, either because they are valuable or because they might cause harm if allowed to diffuse. Encapsulin appears to offer both kinds of functions, because biochemical experiments identified docking sites for a peroxidase and for a ferritin-like protein, with the latter catalyzing the storage of iron as ferrihydrite and the former detoxifying potentially toxic oxygen species. — GJC

    Nat. Struct. Mol. Biol. 10.1038/nsmb.1473 (2008).


    Life Beyond Kinase

    Phosphoinositide 3-kinase (PI3K) enzymes function by transducing the signals from receptor tyrosine kinases and heterotrimeric guanine nucleotide-binding protein (G protein)-coupled receptors. They catalyze the formation of lipid second messengers. Ciraolo et al. explored the biological role of p110β, one of three types of catalytic subunits that make up PI3Ks in mammalian cells. They created mice that express a mutant form of the enzyme that lacks kinase activity. Although complete loss of individual p110 subunits is deadly, the animals expressing the mutant p110β survived, indicating that p110β has functions that are independent of its kinase activity. The mutant animals grew more slowly than normal animals and, as they got older, showed signs of insulin resistance. They also showed impaired signaling from G protein-coupled receptors. In a breast cancer model induced by the ERBB2 oncogene, which signals through PI3K, the mutant animals showed fewer tumors, which grew at a reduced rate. In independent work, Jia et al. explored the effects of tissue-specific depletion of p110β in the liver and provide evidence for kinase-independent roles of p110β and for impaired insulin action in animals lacking p110β. They found that loss of p110β also decreased tumorigenesis in a mouse cancer model caused by loss of the lipid phosphatase PTEN. These studies indicate that tissue-specific actions of p110β may make it a potentially effective target for therapeutic regulation. — LBR

    Sci. Signal. 1, ra3 (2008); Nature 454, 776 (2008).


    Socialized Learning

    The ventral and dorsal neural streams that mediate the visual processing of objects have been described as specializing in what and where, respectively; that is, information about object identity flows through a different channel than that about object location. A related distinction applies to object perception for the purpose of action (where my car is parked) as contrasted with the purpose of recognition (my car is green). Yoon et al. demonstrate that pre-verbal infants (9 months old) form object representations that exhibit a similar dissociation between location and identity—and that the mode of information transmittal dictates the channel of reception. Introducing an explicitly social teaching context by having an actor point to an object while speaking to the infant biased the infant to remember the object's features such that a subsequent presentation of the same object at a second location did not evoke surprise (as assessed by looking time), whereas displaying a new object at the original location did. Conversely, reaching toward an object while verbalizing in an impersonal fashion primed the retention of where information rather than what. Adults, of course, have no difficulty in retaining and retrieving both types of representations, but the nascent neural processing capacities of infants appear to be influenced by social context as well as visual fundamentals. — GJC

    Proc. Natl. Acad. Sci. U.S.A. 105, 13690 (2008).