Editors' Choice

Science  21 Nov 2008:
Vol. 322, Issue 5905, pp. 1164

    Harmonious Agriculture

    1. Andrew M. Sugden

    Long-term or large-scale agriculture is generally associated with substantial losses of biodiversity, yet there is increasing evidence that these losses can be mitigated by appropriate management practices at the landscape scale. Ranganathan et al. show that cultivation of arecanut palm in the Western Ghats region of southern India has not displaced the great majority (90%) of the native forest bird species such as the Malabar grey hornbill. Several factors underlie this favorable outcome: intercropping with other woody species, which creates structural complexity; and proximity to native forest, which is used as a source of mulch. Although similar effects have been observed in other tropical agro-ecosystems over the short term, the arecanut system has been operating in the Western Ghats for at least 2000 years. Hence, it may offer valuable lessons for the harmonizing of tropical agriculture (including biofuel crops) and conservation in the long run. — AMS

    Proc. Natl. Acad. Sci. U.S.A. 105, 10.1073/pnas.0808874105 (2008).


    Out of Thin Air

    1. Gilbert Chin

    In the pre-iPod era, eating a bowl of cold cereal at breakfast offered the opportunity for a detailed reading of the cereal box, on which the uncommon words niacin, thiamin, and riboflavin appeared. Years later, much more reading had explained the role of these trace supplements as coenzymes, needed to forestall the exotic diseases of beriberi and pellagra. Thiamin, also known as vitamin B1, is an invaluable aid in carbohydrate metabolism, specifically during chemical transformations of α-keto compounds. It contains two heterocyclic rings, a thiazole and a pyrimidine; the biosynthesis of the former is well understood; not so for the latter.

    Chatterjee et al. establish by means of biochemical and structural analyses that the Caulobacter crescentus enzyme ThiC catalyzes the conversion of 5-aminoimidazole ribonucleotide (AIR) into 4-amino-5-hydroxymethyl-2-methylpyrimidine phosphate (HMP-P), which is then coupled to the thiazole moiety to give thiamine monophosphate. What makes this reaction more than another bit of esoterica is the intricate rearrangement of AIR atoms effected by ThiC. Of the five carbon atoms in the ribose portion of AIR, C2′ (red) is used to methylate C2 (blue) of the imidazole ring, and C4′ (pink), with C5′ still attached, is inserted in between C4 (olive) and C5 (yellow) of the imidazole ring, expanding it into a pyrimidine. How this is accomplished is not entirely clear, but these authors, as Martinez-Gomez and Downs have achieved recently for Salmonella enterica ThiC, show via in vitro reconstitution that a bound [4Fe-4S] cluster and the co-substrate S-adenosylmethionine participate in what bears the hallmarks of a radical-based mechanism. — GJC

    Nat. Chem. Biol. 4, 10.1038/nchembio.121 (2008); Biochemistry 47, 9054 (2008).


    Fishing for Worms

    1. Laura M. Zahn

    The earthworm Allolobophora chlorotica has two color morphs: pink and green. The facts that these morphs are found in different habitats and crosses between them are sterile have suggested that they represent distinct species. King et al. have examined two mitochondrial genes of A. chlorotica and eight other worms in the United Kingdom. They found that four of the worms, including A. chlorotica, displayed relatively high levels of diversity in the pair of mitochondrial genes. Furthermore, polymorphism markers showed similar divergence for A. chlorotica, where five deeply divergent clades were identified—three clades corresponding to the pink morphotype and two to the green. The relationships among these clades suggest that A. chlorotica, along with three of the other British earthworms, is actually a group of cryptic species as opposed to a single species with phenotypic diversity. — LMZ

    Mol. Ecol. 17, 4684 (2008).


    Tubular Templates

    1. Jake Yeston

    The hydrophobic surfaces of dispersed carbon nanotubes can attract a diverse range of small molecules from a surrounding solution, which in turn interact with one another to form loose assemblies. Thauvin et al. capitalized on this templating behavior by preparing lipids with a photoactive diacetylene group inserted between the polar head and lipophilic tail. After arranging around a nanotube, these lipids could be irradiated in the ultraviolet to rigidify their connections to one another through polymerization (which selectively linked neighboring diacetylenes without inducing covalent attachment to the nanotube surface). Electrophoresis then liberated a batch of uniformly sized assemblies from the nanotube templates, which the authors characterized by transmission electron microscopy and light-scattering measurements. With a polar exterior and a hydrophobic interior hollowed out where the nanotube previously resided, these assemblies proved effective at solubilizing hydrophobic pigments, inhibiting fullerene aggregation, and stabilizing membrane proteins in an aqueous environment. Analysis of their detailed morphology remains underway. — JSY

    Nat. Nanotechnol. 10.1038/nnano.2008.318 (2008).


    Breaking Early and Often

    1. Brooks Hanson

    In 1857, a major earthquake ruptured the central part of the San Andreas fault from near Parkfield in the Carrizo Plain southward to just northeast of Los Angeles (a distance of about 300 km). Surface slip was up to 9 m. Excavations along this break have revealed evidence of several earlier major earthquakes; accurate dating of these events provides an indication of how frequent and regular such major quakes might be. Akciz et al. provide a series of new dates on a section through the fault at Bidart Fan, in the Carrizo Plain, that revise the history of previous quakes. Four previous events are recognized and resolved here, dating from about 1310. The intervals between the quakes range from as short as about 80 years to as long as 200 years; the average recurrence interval is 137 years. This interval is shorter than previously thought and now longer than the time since the 1857 quake. Although the revised dates imply a more regular rupture of the fault, it is not yet clear if the previous major quakes were like that in 1857, or even greater, or ruptured to the north, rather than the south. — BH

    J. Geophys. Res. 10.1029/2007JB005285 (2008).


    Helpful Bystanders

    1. Helen Pickersgill

    Although transformed cells can grow in artificial culture medium on plastic plates, in the body they thrive in very different surroundings. Individual cells are thought to become tumorigenic independently of their local environment, by acquiring genetic and epigenetic changes, although their neighbors may permit and possibly even nourish the growth of transformed cells. Indeed, tumorigenic cells have been shown to secrete signals that induce changes in the surrounding tissues.

    Yang et al. show that in neurofibromatosis type 1 (NF1), a genetic disease that predisposes individuals to tumors such as neurofibromas, the premalignant cells and the cells that form the microenvironment cooperate to promote tumorigenesis. Neurofibromas form from malignant Schwann cells and are associated with peripheral nerves, which are infiltrated by inflammatory mast cells that are derived from the bone marrow. The disease is caused by germline mutations in the NF1 tumor suppressor gene; however, biallelic loss only in the Schwann cells is not sufficient for tumor progression. Instead, the authors find that a heterozygous Nf1 mutation in the nonmalignant infiltrating mast cells is necessary for neurofibroma formation. By blocking mast cell release from the bone marrow, they could delay disease progression. This work upgrades the role of the microenvironment from being permissive for tumorigenesis to being causative. Whether this phenomenon is limited to familial disorders or can also contribute to the development of sporadic tumors remains to be seen. — HP*

    Cell 135, 437 (2008).

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


    Acting at a Distance

    1. Guy Riddihough

    Unfolded proteins are dangerous to the cell; exposing hydrophobic amino acid side chains will promote nonspecific aggregation and interfere with intracellular processes. Chaperones are proteins that assist in the folding and unfolding of other proteins. They are found in all organisms, and among their number are the so-called heat shock proteins (Hsps), which combat heat-induced stress. In Escherichia coli, the heat shock transcription factor σ32 regulates heat-shock gene expression, and it is in turn regulated by Hsps: DnaK (the prokaryote equivalent of Hsp70) and the co-chaperone DnaJ.

    Rodriguez et al. show that DnaK and DnaJ bind independently to distinct domains of σ32 in its native, folded state. The DnaK binding site would normally be occluded on σ32 that is bound to RNA polymerase, suggesting that DnaJ binds σ32 first. The binding of DnaJ destabilizes σ32 at a site in the vicinity of the DnaK binding site, favoring the rapid binding of DnaK once σ32 is released from RNA polymerase. Hsp70 systems in general may act in a similar manner: promoting disassembly and folding of aggregated substrate proteins by altering their conformations from a distance. — GR

    Mol. Cell 32, 347 (2008).