Editors' Choice

Science  01 Oct 2004:
Vol. 306, Issue 5693, pp. 21

    Thinking About Birds

    1. Andrew M. Sugden

    Evolutionary biology has benefited enormously in the past two decades from the application of the life-history approach, which views organisms in the context of conflicts resulting from the allocation of resources to growth, reproduction, foraging, predator avoidance, etc. Cognition is rarely considered in this context; however, if cognition is of benefit to and imposes costs on the individual, then resources devoted to cognitive function might be expected to trade off against other life-history parameters.

    Ricklefs shows that, for birds, the relation of brain mass to body mass and that between egg mass and incubation period may both be indicative of the potential links between cognition and life history. For example, taxonomic groups such as parrots, owls, and corvids, which have complex social or foraging behaviors, have higher than average brain-to-body mass ratios, whereas pigeons, which are not renowned for their behavioral sophistication, rank lower than average. Long incubation periods and postnatal development tend to be associated with these same groups and also with raptors and pelagic seabirds; these birds confront some of the greatest challenges in learning social or foraging skills. Ricklefs argues that behavior based on accumulated experience can logically be treated as an integral part of bird life history and hence sets the stage for an exploration of the underlying mechanisms. — AMS

    Wilson Bull. 116, 119 (2004).


    Gone with the Wind

    1. Linda Rowan

    The double pulsar system J0737-3039 consists of pulsar A (with a period of 23 ms) and pulsar B (2.8 s) in an eclipsing binary orientation. Such rotation-powered pulsars dissipate their rotational energy by giving off magnetized relativistic plasma winds, and, thanks to this unusual system, astronomers can now study these winds.

    Kaspi et al. observed the system with the Green Bank Telescope and found that the eclipse of A lasted longer at lower frequencies. McLaughlin et al. have analyzed this data further and found that the eclipse of A is modulated by the orientation of the rotating magnetic axis of B. These two results are consistent with two similar models of the eclipse proposed by Lyutikov and by Arons et al. They suggest that B has a magnetosphere similar to Earth's, where the plasma wind from A acts like the solar wind; the wind from A collides with the magnetosphere of B, producing synchrotron absorption in the magnetosheath of B that blocks emissions from A, resulting in the eclipse. — LR

    Astrophys. J. 613, L137 (2004); astro-ph/0408297; astro-ph/0403076; astro-ph/0404159.


    Tinker, Tailor

    1. Glibert J. Chin

    The rarity of naturally enriched sources of eukaryotic membrane proteins has made it difficult to pursue classical biochemistry—purification of detergent-solubilized transporters and receptors—to the end point of crystallization and structure determination. Membrane proteins are happiest within their native lipid environment, which, given the diversity of lipid molecules, is antithetical to the homogeneity of a crystal. However, a series of studies on the well-characterized bacterial mechanosensitive channel MscL tackles these challenges and offers some hope for future applications.

    Clayton et al. divided the 15-kD protein into thirds and synthesized the three peptide segments chemically before ligating them into a full-length molecule in the absence of detergents and lipids. Reconstitution into vesicles and patch-clamp measurements confirmed that pressure-sensitive channels had in fact been made. Berrier et al. used a coupled in vitro transcription-translation system to make milligram quantities of MscL in the absence of membranes and were also able to demonstrate activity of the product. Finally, Becker et al. have converted MscL into a completely soluble form by attaching polyethylene- glycol-polyamide tails at four places where the protein would face the hydrophobic interior of the lipid bilayer. Although activity can no longer be measured directly, the structure is by several measures the same as that of the natural protein. — GJC

    Proc. Natl. Acad. Sci. U.S.A. 101, 4764 (2004); Biochemistry 10.1021/bi049049y (2004); J. Mol. Biol. 10.1016/j.jmb.2004.08.062 (2004).


    Container Recycling

    1. Stella M. Hurtley

    Caveolae — microscopic flask-shaped structures at the cell surface — can promote the internalization of a variety of ligands and viruses. What has not been clear is the extent to which cargo internalized via this route might mingle with cargo acquired by classical endocytosis.

    Pelkmans et al. used live cell imaging to monitor caveolar structures and cargos, as well as early endosomal structures, and looked for where and when the internalized cargo was delivered to preexisting endosomal structures. The caveolin containers carried their cargo into the cell and docked with endosomes. Upon fusion with the endosome, the caveolin components did not disperse into bulk endosomal membrane; instead, they remained intact and eventually recycled en bloc back to the cell surface. On the other hand, exposure to the low endosomal pH did induce a cholera toxin cargo to diffuse out of the caveolar patches into the bulk endosomal membrane. The ability of caveolae to maintain structural integrity through a cycle of membrane internalization, fusion, and retrieval may be important in defining when and where cargos are delivered. — SMH

    Cell 118, 767 (2004).


    A Cyclic Inhibitor of Cycling

    1. Julia Fahrenkamp-Uppenbrink

    The introduction of structural constraints into flexible molecules is often used in medicinal chemistry to improve the affinity of the molecules to their target. Andrews et al. have used this approach to design cyclic peptide inhibitors for cyclin-dependent kinase 2 (CDK2), a potential target for intervention in cancer and other proliferative diseases. They based their peptides on the Leu-Phe-Gly cyclin groove recognition motif in the tumor suppressor protein p27KIP1. A covalent link between a side chain and the tail of the peptide mimicks an intramolecular hydrogen bond in the CDK2/cyclin A/p27KIP1 crystal structure. The resulting cyclic compounds showed increased potency as compared with their linear counterparts. — JFU

    Org. Biomol. Chem. 2, 10.1039/b409157d (2004).


    Feeling the Squeeze

    1. Marc S. Lavine

    Under high pressure, atoms in a crystal may rearrange into a more favorable crystal structure or may lose order and become amorphous. Perhaps less well appreciated is that the same can occur in glasses, which show only short-and intermediate-range ordering; these are much harder to study, and there is still debate as to whether the transitions are discrete or continuous.

    Guthrie et al. have examined the behavior of germanium dioxide, a classic network-forming glass, using in situ x-ray diffraction to examine the Ge-Ge and Ge-O correlations, and neutron scattering to look at O-O correlations, as well as molecular dynamics simulations. At ambient pressure, GeO2 forms a standard tetrahedral glass with fourfold Ge-O coordination, and at a pressure of 15 gigapascals they observed a fully octahedral glass with sixfold Ge-O coordination. However, at intermediate pressures, they observed first shrinkage of the Ge-O bond lengths and then a jump to a metastable structure with a coordination number approaching five. The long-lived intermediate phase favors a transition from to low high pressure through two discrete jumps rather than a continuous transformation from fourfold to sixfold coordination. — MSL

    Phys. Rev. Lett. 93, 115502 (2004).

  7. STKE

    Harming Bystanders

    1. Nancy Gough

    Irradiation of cells is known to cause damage to neighboring cells that are not directly exposed to the radiation. Such bystander responses are important when considering the potential damage caused by environmental exposure to radiation or to radiation used in cancer treatment. Although it is known that cells whose nuclei are exposed to radiation can trigger the bystander response, Shao et al. show that even radiation delivered to the cytoplasm of a single cell suffices. The bystander response was measured by the increase of micronuclei (a measure of chromosomal damage) in the cell population when single human glioblastoma T98G cells were exposed to single 3He2+ ions. The bystander response was blocked by the addition of a nitric oxide (NO) scavenger to the medium, and disruption of glycosphingolipid-enriched membrane microdomains (GEMs) with filipin also blocked the bystander response, suggesting that NO, produced through a process that requires GEMs, appears to mediate a signal that leads to chromosomal damage in neighboring cells. — NG

    Proc. Natl. Acad. Sci. U. S. A. 101, 13495 (2004).

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