Editors' Choice

Science  30 Jan 2009:
Vol. 323, Issue 5914, pp. 562

    Fatal Attraction

    1. Andrew M. Sugden

    Two modalities of insect sexual signaling—moth pheromones and Photinus firefly flashing—have been appropriated by predators (the bolar spider and the Photuris firefly, respectively) in an adaptation known as aggressive mimicry. Marshall and Hall have found that predatory Australian katydids of the genus Chlorobalius target amorous male cicadas by imitating the response of the female cicada, thus enticing the male within reach. The katydids are able to copy the species-specific wing-flick sound of the female cicada, which is produced in reply to acoustic features within the male's call and is the audible cue that lures the male onward. Experiments showed that the katydids have the ability to respond effectively to the wide range of songs of a score of cicada species, including species that they have never encountered before. The katydids also appear able to mimic the body-jerking of the female cicadas that accompanies the wing-flick—a behavior that adds a visual element to their response to male song. Although the evolutionary origins of this mimicry remain obscure, the experimentally tractable interaction of katydid and cicada promises to reveal insights into the evolution of insect communication. — AMS

    PLoS ONE 4, e4185 (2009).


    Ready and Waiting

    1. Valda Vinson

    During the biosynthesis of chlorophyll, the central pigment in photosynthesis, the enzyme protochlorophyllide oxidoreductase (POR) catalyzes the trans addition of hydrogen across the C17=C18 double bond of the chlorophyll precursor protochlorophyllide (Pchlide). The light-activated endothermic reaction involves hydride transfer from the cofactor NADPH to C17 of Pchlide and proton transfer from a conserved tyrosine residue in POR to C18 of Pchlide; the mechanistic intricacies, however, have remained unclear.

    Heyes et al. used laser excitation to trigger the addition reaction at temperatures ranging from the physiologic to the cryogenic. Kinetic measurements and density functional theory calculations showed that hydride transfer occurs by quantum-mechanical tunneling and is enabled by a fast dynamical searching for tunneling-ready configurations within the microsecond lifetime of the excited state. Subsequently, proton transfer occurs from the intermediate and involves fast motions that couple to the reaction coordinate. A breakpoint was observed in the temperature dependence of hydride transfer, but not of proton transfer, suggesting that the promoting modes are different for the two steps. — VV

    J. Biol. Chem. 10.1074/jbc.M808548200 (2008).


    Mixed-Up Molecules

    1. Ian S. Osborne

    Cooling atoms, both bosons and fermions, to ultra-low temperatures has provided the opportunity to probe distinct quantum phases of matter. The ability to then trap these atoms, or even molecules, in optical lattices and tune the interactions between them presents the possibility of an ideal and clean quantum system that can act as a surrogate for complex condensed-matter systems in which the tuning parameters may be limited. To date, most boson-boson and boson-fermion mixtures in this context have been formed with atoms of the same element. Forming more complex molecules with multiple elements offers the prospect of adding an anisotropic electric dipole interaction into the mix, thereby opening up a number of applications in quantum information processing and metrology. Voigt et al. demonstrate the formation and trapping of ultracold diatomic heteronuclear molecules using 6Li and 40K fermionic atoms. Forming long-lived bosonic molecules from two fermionic species with such different masses offers a rich parameter space in which to study many-body correlated systems with asymmetric interactions. — ISO

    Phys. Rev. Lett. 102, 20405 (2009).


    Two in One

    1. Pamela J. Hines

    The stress hormone abscisic acid affects a variety of processes in plants, ranging from seed germination to root tissue growth. Nevertheless, identifying specific components in the abscisic acid signal transduction pathways has not been entirely straightforward. Pandey et al. have characterized two related proteins in Arabidopsis that seem likely to function as cell surface sensors of abscisic acid. The proteins, G protein-coupled receptors (GPCRs) types 1 and 2 (GTG1 and GTG2), bind abscisic acid, are widely expressed throughout various plant tissues, and are located at the periphery of cells. Their sequences contain motifs that resemble those of GPCR transmembrane domains and of GTP-binding domains of GTPases. These proteins are highly unusual in possessing both the ligand-binding receptor function and the canonical G protein signaling capacity. — PJH

    Cell 136, 136 (2009).


    Bonded or Not?

    1. Jake Yeston

    Propellane molecules intrigue chemists for a number of reasons, not least because their carbon frameworks resemble the eponymous macroscopic propellers. The [1.1.1] variety comprises three triangles that share an edge at the center, and a persistent question has been whether this shared edge, or bridge, constitutes a strained bond between the atoms at either end of it, or whether these atoms keep an electron to themselves after sharing three others with the vertices. Most evidence points to a bond of some sort between these bridgehead carbons, and similarly between tin atoms in stannous analogs that have been prepared and structurally characterized. Nied et al. have synthesized and obtained the crystal structure of a germanium (Ge) analog by lithium naphthalenide reduction of chloride salts, with the vertices capped by bulky mesityl groups. In the solid state, the bridgehead atoms are roughly 20% farther apart than the length of a typical Ge-Ge single bond. The absence of an electron paramagnetic resonance signal suggests a singlet spin state. Nonetheless, the authors' calculations support a degree of biradical character in the interaction, which is bolstered by observation of facile trimethyltin hydride addition across the bridge. — JSY

    Angew. Chem. Int. Ed. 48, 10.1002/anie.200805289 (2009).


    Collaborative Damage

    1. Helen Pickersgill

    The success of cancer as a disease is due in part to a collaborative effort between tumor cells and other populations of nonmalignant cells in the body. These nonmalignant cells, such as stromal fibroblasts and bone marrow-derived cells, have been shown to be capable of promoting tumor growth and metastasis. Tumor growth is fueled by the formation of new blood vessels in a process known as angiogenesis, which is stimulated by secreted peptides such as vascular endothelial growth factor A (VEGF-A). Antibodies to VEGF have been demonstrated to be effective anticancer agents in the clinic; however, tumor resistance arises rapidly, followed by patient relapse.

    Crawford et al. looked at tumor-associated fibroblasts (TAFs) from a murine lymphoma model that was resistant to antibodies to VEGF. They found that these TAFs were able to stimulate the growth of anti-VEGF-sensitive tumors in vivo, suggesting that the tumor somehow regulates the tumorigenic properties of TAFs. Notably, this stimulation occurred even when VEGF was inhibited, implying that TAFs can influence how the tumor responds to being deprived of a major angiogenic factor. The authors found that TAFs from anti-VEGF-resistant tumors were also able to support angiogenesis, which was due to elevated expression of VEGF-A and another growth promoter, platelet-derived growth factor C (PDGF-C), pointing toward another target for the treatment of cancers (such as pancreatic cancer) that are relatively unresponsive to anti-VEGF therapies. — HP*

    Cancer Cell 15, 21 (2009).

    • *Helen Pickersgill is a locum editor in Science's editorial department.


    Get a Grip

    1. Marc S. Lavine

    The manipulation of cells or other small particles is often accomplished with microgrippers. Examples include devices fabricated with two adjacent strips composed of different materials or kept at different temperatures, so that actuation can be used to grab and release objects. One limitation of this architecture is that the gripper has to be tethered to trigger the actuation. To achieve remote actuation, Leong et al. lithographically patterned bimetallic films of chromium (Cr) and copper (Cu) into fingerlike digits on nickel segments bridged with polymer segments, which acted like bones and joints, respectively. Upon heating or exposure to certain compounds, the polymer would soften or delaminate, allowing the Cr/Cu metal bilayers to flex inward. Grippers were remotely moved by a magnet and could also be rotated so that the digits acted like cutters, as demonstrated by the cutting of the connective tissue. In a related study, Randhawa et al. placed a polymer between the nickel segments that, on exposure to acetic acid, was etched away, closing the gripper. Subsequent exposure to hydrogen peroxide etched the Cu layer, causing the gripper to open. — MSL

    Proc. Natl. Acad. Sci. U.S.A. 106, 703 (2009); J. Am. Chem. Soc. 130, 17238 (2008).

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