Catálogo de publicaciones - revistas

<jats:title>Chloride Control of a Catalyst</jats:title> <jats:p> Allosteric regulation of proteins and enzymes allows their conformation to be controlled by changes in the concentration of effector-binding molecules; reactivity can be controlled by changing access to the active catalytic site. The supramolecular control of conformation through multiple weaker interactions has been exploited in organometallic catalysts that can open or close access to reactive sites around a metal center. <jats:bold> Yoon <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="66" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193928">66</jats:related-article> ) now show how chloride ions can be used to control a rhodium polymerization catalyst in which two metal centers are bridged by a linker bearing aromatic groups. When Cl <jats:sup>−</jats:sup> is present, reactive sites remain available on the metal centers. When Cl <jats:sup>−</jats:sup> is removed by abstracting agents, aromatic groups on one of the other ligands on the Rh centers can bind to the linker to form a triple-layer sandwich structure. Formation of this supramolecular structure blocks access of reactants to the metal centers. </jats:p>

<jats:title>Toward Microbial Taxol</jats:title> <jats:p> Taxol, a minor chemical constituent of yew tree bark, has provided a potent cancer treatment. Production methods presently rely on plant cell cultures. <jats:bold> Ajikumar <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="70" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1191652">70</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6000" page="44" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195014">Liu and Khosla</jats:related-article> </jats:bold> ) engineered <jats:italic>Escherichia coli</jats:italic> cells to produce a key taxol precursor, in which the polycyclic carbon skeleton is intact. The approach relied on optimizing the relative activity of two pathways, the first of which synthesized isoprenoid building blocks that were then stitched together with the second pathway. Accumulation of indole as a by-product inhibited the isoprenoid pathway—an insight that should facilitate more efficient engineered biosynthesis of a wide range of commercially important isoprenoid derivatives. </jats:p>

<jats:title>Indirect Oxidation by Oxygen</jats:title> <jats:p> Partial oxidation of alcohols to aldehydes and ketones must avoid complete oxidation to carbon dioxide and water. <jats:bold> Zope <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="74" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195055">74</jats:related-article> ) examined the partial oxidation of ethanol and glycerol to acids in alkaline aqueous solvents over gold and platinum catalysts. Conversions were highest for gold supported on titania, but studies with isotopically labeled molecular oxygen showed that oxygen incorporated into the acid comes from hydroxide ions. Direct incorporation of oxygen did not occur even for the platinum catalysts, despite the fact that oxygen can dissociate on this metal. Instead, molecular oxygen appeared to regenerate hydroxide ions at the metal surface through the formation of peroxide intermediates. </jats:p>

<jats:title>New Guinea's Ancient Colonies</jats:title> <jats:p> Isolated by water, Australia and New Guinea were some of the last major parts of the world colonized by modern humans. <jats:bold> Summerhayes <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="78" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193130">78</jats:related-article> ; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6000" page="41" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195448">Gosden</jats:related-article> </jats:bold> ) describe an archaeological site in the highlands of New Guinea that sheds light on this migration. The record extends back to nearly 50,000 years ago and thus represents one of the earliest known records. Nuts and yams were widely consumed, and the variety of stone tools discovered implies that the early humans may have cleared forest patches to promote the growth of useful plants. </jats:p>

<jats:title>Auroral Chorus</jats:title> <jats:p> Energetic particles that arrive from near-Earth space produce photon emissions—the aurora—as they bombard the atmosphere in the polar regions. The pulsating aurora, which is characterized by temporal intensity variations, is thought to be caused by modulations in electron precipitation possibly produced by resonance with electromagnetic waves in Earth's magnetosphere. <jats:bold> Nishimura <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="81" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193186">81</jats:related-article> ) present a detailed study of an event that showed a good correlation between the temporal changes in auroral luminosity and chorus emission—a type of electromagnetic wave occurring in Earth's magnetosphere. The results points to chorus waves as the driver of the pulsating aurora. </jats:p>

<jats:title>Improving Yeast for Biofuel Production</jats:title> <jats:p> The biofuels industry uses the yeast <jats:italic>Saccharomyces cerevisiae</jats:italic> to produce ethanol from sugars derived from cornstarch or sugar cane. Plant cell walls are an attractive sugar source; however, yeast does not grow efficiently on cellulose–derived sugars (cellodextrins). <jats:bold> Galazka <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="84" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1192838">84</jats:related-article> , published online 9 September) now show that a model cellolytic fungus <jats:italic>Neurospora crassa</jats:italic> relies on a cellodextrin transport system to facilitate growth on cellulose. Yeast reconstituted with this transport system grew efficiently on cellodextrins, which could potentially improve the efficiency of cellulosic biofuel production. </jats:p>

<jats:title>Closing the Vector Circle</jats:title> <jats:p> The genome sequence of <jats:italic>Culex quinquefasciatus</jats:italic> offers a representative of the third major genus of mosquito disease vectors for comparative analysis. In a major international effort, <jats:bold> Arensburger <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="86" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1191864">86</jats:related-article> ) uncovered divergences in the <jats:italic>C. quinquefasciatus</jats:italic> genome compared with the representatives of the other two genera <jats:italic>Aedes aegypti</jats:italic> and <jats:italic>Anopheles gambiae</jats:italic> . The main difference noted is the expansion of numbers of genes, particularly for immunity, oxidoreductive functions, and digestive enzymes, which may reflect specific aspects of the <jats:italic>Culex</jats:italic> life cycle. <jats:bold> Bartholomay <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="88" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193162">88</jats:related-article> ) explored infection-response genes in <jats:italic>Culex</jats:italic> in more depth and uncovered 500 immune response-related genes, similar to the numbers seen in <jats:italic>Aedes</jats:italic> , but fewer than seen in <jats:italic>Anopheles</jats:italic> or the fruit fly <jats:italic>Drosophila melanogaster</jats:italic> . The higher numbers of genes were attributed partly to expansions in those encoding serpins, C-type lectins, and fibrinogen-related proteins, consistent with greater immune surveillance and associated signaling needed to monitor the dangers of breeding in polluted, urbanized environments. Transcriptome analysis confirmed that inoculation with unfamiliar bacteria prompted strong immune responses in <jats:italic>Culex</jats:italic> . The worm and virus pathogens that the mosquitoes transmit naturally provoked little immune activation, however, suggesting that tolerance has evolved to any damage caused by replication of the pathogens in the insects. </jats:p>

<jats:title>Closing the Vector Circle</jats:title> <jats:p> The genome sequence of <jats:italic>Culex quinquefasciatus</jats:italic> offers a representative of the third major genus of mosquito disease vectors for comparative analysis. In a major international effort, <jats:bold> Arensburger <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="86" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1191864">86</jats:related-article> ) uncovered divergences in the <jats:italic>C. quinquefasciatus</jats:italic> genome compared with the representatives of the other two genera <jats:italic>Aedes aegypti</jats:italic> and <jats:italic>Anopheles gambiae</jats:italic> . The main difference noted is the expansion of numbers of genes, particularly for immunity, oxidoreductive functions, and digestive enzymes, which may reflect specific aspects of the <jats:italic>Culex</jats:italic> life cycle. <jats:bold> Bartholomay <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="88" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1193162">88</jats:related-article> ) explored infection-response genes in <jats:italic>Culex</jats:italic> in more depth and uncovered 500 immune response-related genes, similar to the numbers seen in <jats:italic>Aedes</jats:italic> , but fewer than seen in <jats:italic>Anopheles</jats:italic> or the fruit fly <jats:italic>Drosophila melanogaster</jats:italic> . The higher numbers of genes were attributed partly to expansions in those encoding serpins, C-type lectins, and fibrinogen-related proteins, consistent with greater immune surveillance and associated signaling needed to monitor the dangers of breeding in polluted, urbanized environments. Transcriptome analysis confirmed that inoculation with unfamiliar bacteria prompted strong immune responses in <jats:italic>Culex</jats:italic> . The worm and virus pathogens that the mosquitoes transmit naturally provoked little immune activation, however, suggesting that tolerance has evolved to any damage caused by replication of the pathogens in the insects. </jats:p>

<jats:title>Smoke Gets in Your Lungs</jats:title> <jats:p> Chronic obstructive pulmonary disease (COPD) is a leading cause of death in the United States, primarily caused by cigarette smoking. The chronic inflammation that leads to tissue damage and organ dysfunction in COPD is mediated in large part by neutrophils, a type of granulocytic immune cell. <jats:bold> Snelgrove <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="90" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1190594">90</jats:related-article> , published online 2 September; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6000" page="40" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1196017">Barnes</jats:related-article> </jats:bold> ) now provide an explanation for why neutrophils stick around in the lung during COPD. The neutrophil chemoattractant Pro-Gly-Pro (PGP) is a biomarker for COPD and promotes neutrophil accumulation. The enzyme leukotriene A <jats:sub>4</jats:sub> hydrolase degrades PGP in mice, and its activity was reduced by cigarette smoke both in vivo and in vitro. In contrast, during acute influenza infection in mice, leukotriene A <jats:sub>4</jats:sub> hydrolase functioned normally, allowing for PGP degradation and the resolution of inflammation. Thus, in COPD, cigarette smoking may lead to the accumulation PGP—which, in turn, could keep neutrophils in the lung to drive inflammation and subsequent lung damage and dysfunction. </jats:p>

<jats:title>Gaining from a Loss</jats:title> <jats:p> Mitotic recombination can cause a cell carrying heterozygous mutations in a tumor suppressor gene to lose the wild-type copy of the gene, setting the cell on the pathway to uncontrolled growth. But can mitotic recombination have beneficial effects in other settings—that is, lead to phenotypic correction of a diseased cell by facilitating loss of the disease-causing mutation? <jats:bold> Choate <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="94" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1192280">94</jats:related-article> , published online 26 August; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6000" page="46" related-article-type="in-this-issue" vol="330" xlink:href="10.1126/science.1195991">Davis and Candotti</jats:related-article> </jats:bold> ) now find evidence for this type of event in a rare skin disease called ichthyosis with confetti (IWC). Patients with IWC display severe scaling of the skin but have widespread patches of normal skin that reflect clonal expansion of revertant cells. The revertant cells showed loss of heterozygosity on chromosome 17q and, as a result of mitotic recombination, these cells selectively lost dominant disease-causing mutations in the keratin 10 gene ( <jats:italic>KRT10</jats:italic> ), but retained the wild-type copy of the gene. </jats:p>