Catálogo de publicaciones - revistas

<jats:title>Unraveling Entanglement</jats:title> <jats:p> Entanglement is a curious property of some quantum mechanical systems, exploited in applications such as quantum information processing. <jats:bold> Walter <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1205" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1232957">1205</jats:related-article> ) used an algebraic geometry approach to represent the entanglement of a multiparticle system in a pure state in the geometric space whose axes are associated with the properties of the individual particles. In that space, entanglement classes—collections of entangled states that can be transformed into each other—correspond to different convex polytopes, making it possible to distinguish between the classes. </jats:p>

<jats:title>Sonic Boom from Below</jats:title> <jats:p> Seismic shear waves released by an earthquake typically far outpace motion along the fault surface. Occasionally, however, earthquakes along strike-slip faults appear to propagate so that the rupture velocity is faster than shear waves, creating a sort of sonic boom along the fault surface. <jats:bold> Passelègue <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1208" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1235637">1208</jats:related-article> ) were able to reproduce and measure these so-called supershear ruptures in stick-slip experiments with two pieces of granite under high applied normal stress. Much like during a sonic boom when a plane travels faster than the speed of sound, the ruptures created a shock wave in the form of a Mach cone around the rupture front. </jats:p>

<jats:title>Essential Novelty</jats:title> <jats:p> The evolution of essential function for newly originated genes presents a conundrum, in that prior to the gene's origin either the essential function was absent or else performed by another gene or set of genes. In order to better understand how new genes acquire essential function, <jats:bold> Ross <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1211" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1234393">1211</jats:related-article> ) investigated the origin of the <jats:italic>Drosophila</jats:italic> gene <jats:italic>Umbrea. Umbrea</jats:italic> became an essential protein in certain <jats:italic>Drosophila</jats:italic> species through the gain of localization at the centromere and a role in chromosome segregation. </jats:p>

<jats:title>Thank Your Mother</jats:title> <jats:p> Maternal effects and influence can sometimes prepare unborn offspring for some of the environmental conditions they may face. <jats:bold> Dantzer <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1215" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1235765">1215</jats:related-article> , published online 18 April) monitored a population of red squirrels and found that both natural and artificially induced increases in the number of conspecific calls increased the growth rate of pups because of increased glucocorticoid levels in the mother. The density stress experienced by mothers thus appears to stimulate them to produce pups that will grow faster and hopefully outcompete the many other pups expected to be produced in the dense population. </jats:p>

<jats:title>Lock and Load in the Cold</jats:title> <jats:p> Muscle extensibility can act as an energy storage vehicle, like springs bouncing back after being compressed. <jats:bold> George <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1217" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1229573">1217</jats:related-article> , published online 25 April) now show that energy can also be stored within muscles as a function of their natural temperature gradient. In hawkmoth muscle myofilaments, reduced cross-bridge cycling regionally constrains myofilaments, resulting in a "lock-spring lattice" that enables elastic energy storage as both the myofilaments and cross-bridges deform. Elastic energy stored in cross-bridges that remain bound and elastically deformed at the end of the first half of a contraction cycle can be released during the second half, thus serving as an additional elastic force. Such "bonus" energy may be especially important given the high energetic demands of flight, but because temperature gradients are a natural result of energy generation and heat dissipation in muscle, this mechanism could be more broadly important in locomotion systems. </jats:p>

<jats:title>Improve the System</jats:title> <jats:p> A "systems biology" approach may clarify, for example, how particular proteins determine sensitivity of bacteria to extremes of temperature. <jats:bold> Chang <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1220" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1234012">1220</jats:related-article> ) integrated information on protein structure with a model of metabolism, thus associating the protein structure of enzymes with their catalyzed metabolic reactions. The effects of temperature on susceptible proteins could be predicted and the key reactions that were likely to mediate sensitivity of bacteria to extremes of temperature were identified. Indeed, engineered thermotolerant proteins could be substituted for sensitive ones to improve the growth of thermosensitive strains of bacteria. Such control could come in handy when engineering strains of bacteria to produce compounds of industrial or therapeutic value. </jats:p>

<jats:title>Sending Out an ROS</jats:title> <jats:p> The global imprint of biological activity in aquatic environments is often considered a consequence of enzyme-mediated redox reactions that support metabolic activity, such as reducing oxygen during respiration. But some organisms also release redox-active reactive oxygen species (ROS) into the environment—to acquire trace metals or to prevent viral infections—which can influence global processes like nutrient availability and contaminant transport. Photosynthetic organisms like phytoplankton are thought to be the primary biological source of ROS in freshwater and marine environments. However, <jats:bold> Diaz <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1223" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1237331">1223</jats:related-article> , published online 2 May; see the Perspective by <jats:bold> <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1176" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1240195">Shaked and Rose</jats:related-article> </jats:bold> ) now show that a broad range of ecologically and phylogenetically diverse heterotrophic bacteria also produce large quantities of superoxide. Production rates vary widely across 30 common bacterial isolates but in some cases were greater than production rates of phytoplankton. Because these bacteria do not require light to grow, they may be the dominant source of ROS in dark environments like the deep ocean, terrestrial soils, or lake sediments. </jats:p>

<jats:title>Getting Active</jats:title> <jats:p> The P450 cytochromes are a family of enzymes that contain a heme cofactor and catalyze the oxidation of organic substrates, including drugs. Protein partners are required to deliver electrons to P450. Insight into this mechanism has come from studies of bacterial P450cam; however, a lack of structures of redox complexes has hindered understanding. <jats:bold> Tripathi <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1227" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1235797">1227</jats:related-article> ) describe the high resolution crystal structures of oxidized and reduced P450cam complexed with its redox partner putidaredoxin (Pdx). Pdx favors binding to the more open form of P450cam, which enables establishment of the water-mediated H-bonded network required for proton-coupled electron transfer and O <jats:sub>2</jats:sub> activation. </jats:p>

<jats:title>Tolerance Needed</jats:title> <jats:p> It's a common enough occurrence: You're sick as a dog with a cold, but the person in the office next door just has a few sniffles. What accounts for this difference? Most commonly, these sorts of differences are chalked up to differences in resistance—perhaps you have higher viral loads than your office mate. But such differences can also involve differences in the ability to tolerate the same amount of virus. Deciphering the contribution of resistance versus tolerance, however, is difficult. <jats:bold> Jamieson <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1230" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1233632">1230</jats:related-article> , published online 25 April) studied a mouse model of viral and bacterial co-infection where tolerance and resistance could be separated. Mice infected with influenza virus were more likely to succumb to a secondary infection with <jats:italic>Legionella pneumophila</jats:italic> as a result of impaired tolerance to tissue damage, rather than because of a difference in bacterial burden. </jats:p>

<jats:title>What Causes Obsessive Compulsive Disorder?</jats:title> <jats:p> Obsessive compulsive disorder is a severe, chronic mental illness that affects millions of individuals. However, the mechanisms underlying this disease are still largely unknown (see the Perspective by <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1174" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1239652"> <jats:bold>Rauch and Carlezon Jr.</jats:bold> </jats:related-article> ). <jats:bold> Ahmari <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1234" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1234733">1234</jats:related-article> ) stimulated glutamatergic pathways between the orbitofrontal cortex and the ventromedial striatum and used grooming to assess obsessive compulsive behavior in mice. Repetitive stimulation over days triggered changes in the neuronal responses of the ventromedial striatum. Over time, the behavior of the animals became independent of stimulation and could be prevented by the antidepressant fluoxetine. <jats:bold> Burguière <jats:italic>et al.</jats:italic> </jats:bold> (p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6137" page="1243" related-article-type="in-this-issue" vol="340" xlink:href="10.1126/science.1232380">1243</jats:related-article> ) investigated the neural basis of obsessive compulsive symptoms in a mutant mouse that showed excessive expression of a conditioned form of grooming. </jats:p>