Catálogo de publicaciones - revistas

<jats:title>Toward Quantum Computing</jats:title> <jats:p> Quantum computers are expected to be able to tackle problems that would take classical computers many lifetimes to solve. Nonabelian states of matter can store quantum information in their topology, making them immune to environmental perturbations. A physical system expected to possess this unusual property is the fractional quantum Hall state at filling factor ν = 5/2. <jats:bold> Tiemann <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="828" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1216697">828</jats:related-article> , published online 26 January) used nuclear magnetic resonance to measure the polarization of the 5/2 state and found that it is fully polarized—a finding consistent with a nonabelian state—keeping hopes for topological fault-tolerant quantum computing alive. </jats:p>

<jats:title>Nanorobots Deliver</jats:title> <jats:p> DNA aptamers are short strands that have high binding affinity for a target protein that can be used as triggers for releasing cargo from delivery vehicles. <jats:bold> Douglas <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="831" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1214081">831</jats:related-article> ) used this strategy to design DNA origami “nanorobots”—complex shaped structures created by manipulating a long DNA strand through binding with shorter “staple” strands—that could deliver payloads such as gold nanoparticles or fluorescently labeled antibody fragments. These nanorobots were designed to open in response to specific cell-surface proteins, releasing molecules that triggered cell signaling. </jats:p>

<jats:title>From Plant to Plastic</jats:title> <jats:p> Petroleum is primarily used as fuel, but it is also used in the production of plastics. Thus, if biomass were to replace petroleum as society's carbon feedstock, a means of deriving ethylene and propylene—the principal building blocks of today's commodity plastics— would be helpful. Well-known Fischer-Tropsch (FT) catalysts can transform gasified biomass into a range of hydrocarbon derivatives, but ethylene and propylene tend to constitute a small fraction of the overall product distribution. <jats:bold> Torres Galvis <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="835" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215614">835</jats:related-article> ) now demonstrate a class of iron catalysts on relatively passive supports (carbon nanofibers or α-alumina) that robustly directed the FT process toward light olefins. </jats:p>

<jats:title>Driving Forces</jats:title> <jats:p> The physical properties that control the motions of Earth's tectonic plates are difficult to predict accurately on a global scale. Large-scale geodynamic models are continually becoming more powerful, but controversies remain regarding plate-driving forces. <jats:bold>Ghosh and Holt</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="838" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1214209">838</jats:related-article> ) present a global geodynamic model that achieves a high level of accuracy in fitting surface plate motions, plate boundary deformation, and intraplate stress fields. The model identifies regions where mantle drag drives plate motion and regions where the drag resists plate motion. Based on the relative magnitude of mantle drag forces and lithospheric buoyancies contributing to the stress field, the model also quantifies absolute viscosity—a parameter that has been notoriously difficult to predict for Earth's interior. </jats:p>

<jats:title>Plastid Origins</jats:title> <jats:p> The glaucophytes, represented by the alga <jats:italic>Cyanophora paradoxa</jats:italic> , are the putative sister group of red and green algae and plants, which together comprise the founding group of photosynthetic eukaryotes, the Plantae. In their analysis of the genome of <jats:italic>C. paradoxa</jats:italic> , <jats:bold> Price <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="843" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1213561">843</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="6070" page="809" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1218515">Spiegel</jats:related-article> </jats:bold> ) demonstrate a unique origin for the plastid in the ancestor of this supergroup, which retains much of the ancestral diversity in genes involved in carbohydrate metabolism and fermentation, as well as in the gene content of the mitochondrial genome. Moreover, about 3.3% of nuclear genes in <jats:italic>C. paradoxa</jats:italic> seem to carry a signal of cyanobacterial ancestry, and key genes involved in starch biosynthesis are derived from energy parasites such as Chlamydiae. Rapid radiation, reticulate evolution via horizontal gene transfer, high rates of gene divergence, loss, and replacement, may have diffused the evolutionary signals within this supergroup, which perhaps explains previous difficulties in resolving its evolutionary history. </jats:p>

<jats:title>Adapting to the Cold</jats:title> <jats:p> The gating of potassium channels is temperature sensitive, suggesting that these channels must adapt to function efficiently in the extreme cold. <jats:bold>Garrett and Rosenthal</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="848" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1212795">848</jats:related-article> , published online 5 January; see the Perspective by <jats:bold> Ö <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6070" page="805" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1219300">hman</jats:related-article> </jats:bold> ) show that the coding sequences for delayed rectifier potassium channels from an Antarctic and a tropical octopus differed at only four positions and gave functionally identical channels when expressed in <jats:italic>Xenopus</jats:italic> oocytes. A variation in temperature responses instead came from extensive messenger RNA editing. In particular, an edit that recoded an isoleucine to a valine in the pore of the Antarctic octopus channel greatly accelerated gating kinetics. </jats:p>

<jats:title>A Lipid-Sensing GPCR</jats:title> <jats:p> Sphingosine 1-phosphate (S1P) is a sphingolipid that binds to the G protein–coupled receptor subtype 1 (S1P <jats:sub>1</jats:sub> ) to activate signaling pathways involved in regulation of the vascular and immune systems. <jats:bold> Hanson <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="851" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215904">851</jats:related-article> ) determined the crystal structure of S1PR in complex with an antagonist sphingolipid mimic. Ligand access to the receptor from the extracellular milieu is occluded, and a gap between helices I and VII may provide ligand access from within the membrane. The structural information, together with mutagenesis and structure activity relationship data, provides insight into the molecular recognition events that modulate signaling. </jats:p>

<jats:title>From NO to Complement</jats:title> <jats:p> To complete their development in the mosquito, ookinetes—reproductive stages of the malaria parasite <jats:italic>Plasmodium</jats:italic> —must traverse the midgut epithelium and avoid being detected and lysed by the mosquito complement system thioester-containing protein 1 (TEP1). <jats:bold> Oliveira <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="856" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1209678">856</jats:related-article> , published online 26 January) identified mosquito heme peroxidase (HPX2) and a reduced form of nicotinamide adenine dinucleotide phosphate (NADPH) oxidase 5 (NOX5) as key enzymes that are induced in midgut cells during ookinete invasion that, together with nitric oxide synthase, mediate protein nitration. The HPX2-NOX5 system potentiates nitric oxide toxicity and is critical for mosquitoes to mount an effective antiplasmodial response. Epithelial nitration and TEP1-mediated lysis appear to act sequentially in parasite killing, and epithelial nitration may help to promote the mosquito complement cascade. </jats:p>

<jats:title>Flagellin Takes Its Toll</jats:title> <jats:p> The immune system recognizes bacterial infections by binding to conserved molecular fragments derived from the invading bacteria. Molecular mimics of these bacterial determinants have the potential to boost the immunogenicity of vaccines. <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="859" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1215584">859</jats:related-article> ) now report the crystal structure of the D1/D2 fragment of <jats:italic>Salmonella</jats:italic> flagellin, a protein critical for the motility of flagellated bacteria, with the ectodomain of zebrafish Toll-like receptor 5 (TLR5), the host receptor that binds to flagellin and signals the immune system to react. Two TLR5-flagellin heterodimers dimerized into a 2:2 tail-to-tail signaling complex. Mutational analysis and use of human TLR5 validated the signaling mechanism, which is conserved from zebrafish to humans. </jats:p>

<jats:title>Faculty Fates</jats:title> <jats:p> Academic careers in STEM (science, technology, engineering, and math) include challenges that may differ depending on gender. <jats:bold>Kaminski and Geisler</jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" page="864" related-article-type="in-this-issue" vol="335" xlink:href="10.1126/science.1214844">864</jats:related-article> ) analyzed the retention rates for tenure-track faculty at 14 U.S. universities in various disciplines. College catalogs, departmental Web sites, and other public sources of information were used to follow the academic careers of nearly 3000 STEM faculty. Except in mathematics faculties—where women left a couple of years earlier than men—generally, women and men were retained and promoted at the same rate. </jats:p>