This Week in Science

Science  18 Apr 2008:
Vol. 320, Issue 5874, pp. 285
  1. Acid Tests


    One worrying consequence of increasing atmospheric carbon dioxide is ocean acidification. As the oceans absorb carbon dioxide, the pH will fall, making it more difficult for calcifying organisms such as corals to produce and maintain their skeletons. This change could have disastrous consequences for many types of marine life, and also serious repercussions for terrestrial species including humans. Now Iglesias-Rodriguez et al. (p. 336) report that, contrary to expectations, high atmospheric carbon dioxide levels may actually increase calcification by the coccolithophore species Emiliania huxleyi. Thus, the ecological and biogeochemical effects of rising atmospheric carbon dioxide levels may not be straightforward.

  2. Stocking the Malaria Arsenal

    An unassuming plant from China shows promise as a source of powerful antimalarial drugs. Artemisinin and its various derivatives, often delivered in combination with preexisting anti-malarial drugs, are proving tough in the fight against malaria. White (p. 330) reviews the derivation of the artemisinin arsenal, its current deployment, and how combination artemisinin therapies fit in with global policy initiatives to put malaria to rest.

  3. One-Way Ticket for Influenza

    During the past 5 years, influenza epidemics have been seeded by viruses that originated in east and Southeast Asia, probably from temporally overlapping epidemics rather than by persistence. Russell et al. (p. 340) have taken 13,000 isolates of influenza virus and analyzed the HA1 domain of the hemagglutinin to investigate the ancestry of the circulating strains. Travel and trade connections explain the global dissemination of influenza strains on a one-way route out of Asia, taking about 6 to 9 months to reach Europe and North America. Several months later, these strains arrive at their evolutionary graveyard in South America. Thus, the antigenic characteristics of currently circulating viruses in east and Southeast Asia may be key to forecasting vaccine needs.

  4. Math and Music

    Musicians and composers use a variety of techniques for grouping notes that reflect an intuitive sense of their relatedness. For example, major and minor triads (chords of three notes) are considered to be similar, even though they do not sound exactly identical. Although such intuitions are common, they are difficult to quantify. Callender et al. (p. 346; see the Perspective by Hall) use the methods of geometry to model how western musicians traditionally classify pitch sequences. Geometrical spaces exist in which chord types can be represented, and distance between chords in the mathematical sense corresponds to similarity in the intuitive sense. This translation of musical theory into the language of contemporary geometry provides a framework for discerning relationships among musical works and tools for interpreting compositions.

  5. Solid-State Spin Control


    The coherent control of a single spin on a quantum dot is a fundamental requirement for solidstate quantum information processing. Berezovsky et al. (p. 349) demonstrate such coherent manipulation of a single electron spin on a quantum dot using ultrafast optical pulses. Using the optical Stark effect and a series of ultrafast optical pulses, they rotate the single spin through arbitrary angles up to π radians on picosecond time scales. The observed spin rotations constitute true single-qubit operations, performed on a time scale much shorter than the coherence time, and are readily scalable to the large number of operations needed for practical applications. However, in the case of the nitrogen vacancy (NV) in diamond, the single spin to be manipulated sits in a bath of background spins, which can be detrimental to the quantum dynamics of the NV center. Hanson et al. (p. 352, published online 13 March 2008; cover) present experimental and numerical modeling aimed at understanding the coupling and eventually controlling the coherence of the quantum dynamics of the spin of the NV center.

  6. Cellular Orienteering

    How do cells control membrane retraction and the direction of cell movement? Witze et al. (p. 365; see the Perspective by Bowerman) examined cells responding to the developmental signaling protein Wnt. Cultured human melanoma cells responded to Wnt5A by accumulating a cluster of receptor, adhesion, cytoskeletal, and motor proteins near the cell surface. When cells were orienting in a gradient of chemokine concentration, the protein cluster was localized asymmetrically at the posterior of the cell. This structure may help cells integrate the actions of receptors that mediate cell adhesion and cell signaling with cytoskeletal components to control membrane retraction and the direction of cell movement.

  7. The Yin and Yang of Neuronal Maintenance

    During development, more peripheral neurons project to target organs than are ultimately needed. The neurons then compete for neurotrophic factors that are secreted by target cells. Deppmann et al. (p. 369, published online 6 March 2008) now explain how some neurons manage to survive, whereas others die, even though they have similar access to sustaining growth factors. The answer appears to depend on a series of feedback loops. Nerve growth factor (NGF) secreted by target cells not only stimulates expression of its own receptor, but also promotes expression of other factors that can cause neuronal cell death. The surviving neurons appear to have sufficiently strong NGF signaling to withstand the antagonistic signals.

  8. Improving on Immunoglobulins

    Intravenous immunoglobulin (IVIG) therapy uses pooled fractions of human serum immunoglobulin G (IgG) to treat a variety of conditions, including autoimmune diseases. The treatment relies in some way on the anti-inflammatory activity of a subfraction of the immunoglobulins applied, and sialyation of N-linked sugars in the constant portion of the IgG chains is known to be important. Now, Anthony et al. (p. 373) define a specific sialic acid-galactose linkage required for anti-inflammatory activity. A recombinant sialylated IgG Fc fragment could recapitulate the anti-inflammatory activity of IVIG, suggesting that it might be possible to capture the effectiveness of IVIG without the need for human donors.

  9. Reconstitution of Bacterial Pilus Assembly

    Adhesive pili are filamentous protein complexes on bacterial surfaces, which mediate the adhesion of pathogenic bacteria to host tissues. Pili serve as a paradigm for studying ordered macromolecular assembly reactions at the bacterial cell membrane. Nishiyama et al. (p. 376, published online 27 March 2008) now describe the complete in vitro reconstitution of an assembly and secretion system for adhesive pili from purified pilus proteins, using type 1 pili from uropathogenic Escherichia coli. The reconstitution reveals how a protein catalyst can accelerate the ordered assembly of a supramolecular protein complex.

  10. Receptor-dsRNA-Receptor

    Toll-like receptors recognize molecules associated with pathogens and initiate inflammatory responses. For example, Toll-like receptor 3 (TLR3) recognizes double-stranded RNA (dsRNA), an intermediate in viral replication. The TLR3 ectodomain binds as a dimer to dsRNA, but the molecular basis for signaling remains unclear. Liu et al. (p. 379) now report the structure of a complex between two mouse TLR3-ectodomains and dsRNA. Two horseshoe-shaped TLR3-ectodomain monomers bind to opposite faces of the dsRNA through their N- and C-termini and dimerize through their C-termini so that the N-termini are at opposite ends of the linear dsRNA molecule. This dimerization mode could mediate signal transduction by facilitating dimerization of the receptor cytoplasmic domains.

  11. Little Change, Large Consequence


    Occasionally, small changes in sequence change the overall architecture of large protein assemblies. One system for understanding protein assembly is the bacterial flagellar filament, the prototype of which comes from Salmonella and contains eleven protofilaments. Galkin et al. (p. 382), now show that the homologous flagellar filament of Camplyobacter contains only seven protofilaments. The difference may be related to sequence divergence in a region of flagellin that in Salmonella is involved in coiled-coil formation and is recognized by the vertebrate Toll-like receptor 5 (TLR5). Campylobacter is not recognized by TLR5, and its evasion may have driven the change in quaternary structure.

  12. Antidepressants and Adult Brain Plasticity

    The mechanism of action of antidepressant drugs is still unclear, but neuronal plasticity may be important. Maya Vetencourt et al. (p. 385) investigated whether chronic treatment with antidepressants restores plasticity in the adult visual system of the rat. The authors used two classical models of plasticity, the ocular dominance shift of visual cortical neurons following monocular deprivation and the recovery of visual function in the adult after long-term monocular deprivation. Surprisingly, chronic administration of antidepressants increased brain-derived neurotrophic factor expression in the visual cortex and reduced intracortical inhibition, thus restoring ocular dominance plasticity in adulthood and promoting the recovery of vision in adult rats. Antidepressants may thus increase plasticity throughout the brain, potentially explaining their antidepressant effects.

  13. Atomlike Orbitals of C60

    Orbital hybridization between atoms underlies the formation of chemical bonds, and the familiar symmetry of atomic orbitals results from the electrons moving in a central potential. Feng et al. (p. 359) have explored whether molecular orbitals in C60, which is nearly spherically symmetric, could mimic atomic orbitals. They present scanning tunneling microscopy images of C60 adsorbed on clean and partially oxidized copper surfaces, both as isolated molecules and as aggregates such as dimers, wires, and partial monolayers. They can observe the low-lying unoccupied molecular orbitals (LUMOs) of C60 in scans of the variation of tip height with applied bias. In the aggregates, the first three unoccupied states, which lie at energies below 3.5 electron volts, are localized, whereas higher excited states were delocalized and resemble molecular orbitals that would form from simpler atomic orbitals. The authors suggest that C60 acts as a “superatom,” in that the interaction of an electron with its screening charge creates a central potential that gives rise to atomlike orbitals.

  14. Graphene Device Diversity

    The massless charge carriers, the particular energy band diagram combined with the mechanical properties of graphene, have been subjected to intense investigation for fundamental and applied studies. Fabricating quantum-dot devices of various diameters out of a single layer of graphene, Ponomarenko et al. (p. 356; see the Perspective by Westervelt) show that the devices exhibit a diverse set of characteristic properties that are size dependent. The largest quantum dots show conventional single-electron transistor action; the intermediate dots exhibit chaotic behavior in terms of the energy levels, similar to light bouncing around a cavity; and the smallest devices behave as quantum point contacts operational at room temperature.

  15. Easy Life in the Lab

    Single deletions of most genes in yeast do not cause a recognizable phenotype in yeast cells maintained in the lab. Is this because many genes are unnecessary or because of compensation by other mechanisms? In over 1000 chemical genomic experiments, Hillenmeyer et al. (p. 362) exposed yeast cultures to hundreds of small molecules or to various environmental stresses and checked for growth defects in cells with individual deletions. Most genes did indeed have an important biological function. Nearly all were essential for optimal growth when yeast cells did not have the luxury of growing on traditional “rich” medium in the lab.