Catálogo de publicaciones - revistas

<jats:title>To eat or not to eat</jats:title> <jats:p> Melanocortin receptor 4 (MC4R) plays a role in regulating food intake: Its activation by a stimulating hormone inhibits appetite, whereas binding to a natural antagonist promotes appetite. Complementing a recent structure of MC4R in an inactive conformation, Israeli <jats:italic>et al.</jats:italic> present the structure bound to setmelanotide, a weight-control drug, and its G protein–signaling partner (see the Perspective by Farooqi). This work reveals the mechanism of MC4R activation and explains why setmelanotide acts as a potent agonist, whereas a structurally similar compound, SHU9119, is an inhibitor. The structure also provides insight into the contribution of mutations in MCR4 to weight-regulation disorders. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abf7958, this issue p. <jats:related-article issue="6544" page="808" related-article-type="in-this-issue" vol="372">808</jats:related-article> ; see also abi8942, p. <jats:related-article issue="6544" page="792" related-article-type="in-this-issue" vol="372">792</jats:related-article> </jats:p>

<jats:title>Unmitigated spread in Brazil</jats:title> <jats:p> Despite an extensive network of primary care availability, Brazil has suffered profoundly during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Using daily data from state health offices, Castro <jats:italic>et al.</jats:italic> analyzed the pattern of spread of COVID-19 cases and deaths in the country from February to October 2020. Clusters of deaths before cases became apparent indicated unmitigated spread. SARS-CoV-2 circulated undetected in Brazil for more than a month as it spread north from Sã o Paulo. In Manaus, transmission reached unprecedented levels after a momentary respite in mid-2020. Faria <jats:italic>et al.</jats:italic> tracked the evolution of a new, more aggressive lineage called P.1, which has 17 mutations, including three (K417T, E484K, and N501Y) in the spike protein. After a period of accelerated evolution, this variant emerged in Brazil during November 2020. Coupled with the emergence of P.1, disease spread was accelerated by stark local inequalities and political upheaval, which compromised a prompt federal response. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abh1558 and abh2644, this issue p. <jats:related-article issue="6544" page="821" related-article-type="in-this-issue" vol="372">821</jats:related-article> and p. <jats:related-article issue="6544" page="815" related-article-type="in-this-issue" vol="372">815</jats:related-article> </jats:p>

<jats:title>Unmitigated spread in Brazil</jats:title> <jats:p> Despite an extensive network of primary care availability, Brazil has suffered profoundly during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic. Using daily data from state health offices, Castro <jats:italic>et al.</jats:italic> analyzed the pattern of spread of COVID-19 cases and deaths in the country from February to October 2020. Clusters of deaths before cases became apparent indicated unmitigated spread. SARS-CoV-2 circulated undetected in Brazil for more than a month as it spread north from Sã o Paulo. In Manaus, transmission reached unprecedented levels after a momentary respite in mid-2020. Faria <jats:italic>et al.</jats:italic> tracked the evolution of a new, more aggressive lineage called P.1, which has 17 mutations, including three (K417T, E484K, and N501Y) in the spike protein. After a period of accelerated evolution, this variant emerged in Brazil during November 2020. Coupled with the emergence of P.1, disease spread was accelerated by stark local inequalities and political upheaval, which compromised a prompt federal response. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abh1558 and abh2644, this issue p. <jats:related-article issue="6544" page="821" related-article-type="in-this-issue" vol="372">821</jats:related-article> and p. <jats:related-article issue="6544" page="815" related-article-type="in-this-issue" vol="372">815</jats:related-article> </jats:p>

<jats:p>Transmission electron microscopes use electrons with wavelengths of a few picometers, potentially capable of imaging individual atoms in solids at a resolution ultimately set by the intrinsic size of an atom. However, owing to lens aberrations and multiple scattering of electrons in the sample, the image resolution is reduced by a factor of 3 to 10. By inversely solving the multiple scattering problem and overcoming the electron-probe aberrations using electron ptychography, we demonstrate an instrumental blurring of less than 20 picometers and a linear phase response in thick samples. The measured widths of atomic columns are limited by thermal fluctuations of the atoms. Our method is also capable of locating embedded atomic dopant atoms in all three dimensions with subnanometer precision from only a single projection measurement.</jats:p>

<jats:title>A boost for brain–computer interfaces</jats:title> <jats:p> The finely controlled movement of our limbs requires two-way neuronal communication between the brain and the body periphery. This includes afferent information from muscles, joints, and skin, as well as visual feedback to plan, initiate, and execute motor output. In tetraplegia, this neural communication is interrupted in both directions at the level of the spinal cord. Brain–computer interfaces have been developed to produce voluntary motor output controlled by directly recording from brain activity. Flesher <jats:italic>et al.</jats:italic> added an afferent channel to the brain–computer interface to mimic sensory input from the skin of a hand (see the Perspective by Faisal). The improvements achieved by adding the afferent input were substantial in a battery of motor tasks tested in a human subject. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abd0380, this issue p. <jats:related-article issue="6544" page="831" related-article-type="in-this-issue" vol="372">831</jats:related-article> ; see also abi7262, p. <jats:related-article issue="6544" page="791" related-article-type="in-this-issue" vol="372">791</jats:related-article> </jats:p>

<jats:title>Engineering suitable redox molecules</jats:title> <jats:p> In a flow battery, catholyte and anolyte are stored in separate tanks, and pumps are used to circulate the fluids into a stack with electrodes separated by a thin membrane. Such batteries are ideal for large-scale grid storage applications; however, suitable redox molecules are currently limited. Feng <jats:italic>et al.</jats:italic> used “molecular engineering” to modify an inexpensive precursor (9-fluorenone) as the basis for an organic-based redox flow battery (see the Perspective by Hu and Liu). The authors tested a series of variant molecules in a redox flow battery in which the reactions involve reversible ketone hydrogenation and dehydrogenation in an aqueous electrolyte. These reactions have advantageous features, including two-electron redox and operation in air and at elevated temperatures (50°C), that are more suitable for real-world applications. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abd9795, this issue p. <jats:related-article issue="6544" page="836" related-article-type="in-this-issue" vol="372">836</jats:related-article> ; see also abi5911, p. <jats:related-article issue="6544" page="788" related-article-type="in-this-issue" vol="372">788</jats:related-article> </jats:p>

<jats:title>Quantifying translation in space and time</jats:title> <jats:p> During development, precise control of gene expression establishes reproducible patterns, leading to the formation of organs at the right time and place. The emergence of developmental patterns has been primarily studied at the transcriptional level, but the fate of these transcripts has received little attention. Dufourt <jats:italic>et al.</jats:italic> used the SunTag labeling method to image the dynamics of translation of individual messenger RNA (mRNA) molecules in living fruit fly embryos. This work revealed “translation factories”—clusters of mRNA and translation machinery—and heterogeneities in the efficiency of translation between identical mRNAs. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abc3483, this issue p. <jats:related-article issue="6544" page="840" related-article-type="in-this-issue" vol="372">840</jats:related-article> </jats:p>

<jats:title>Finding the breaking point</jats:title> <jats:p> A superfluid can flow without viscosity but only if the speed of the flow is lower than the so-called critical velocity. Sobirey <jats:italic>et al.</jats:italic> measured the critical velocity of a system of ultracold fermionic atoms confined to two dimensions. The researchers trapped a gas of lithium-6 atoms in a box-shaped potential and then moved another, periodic potential through the trap. The response of the gas to this perturbation showed a sudden increase when the speed of the periodic potential reached the critical velocity. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abc8793, this issue p. <jats:related-article issue="6544" page="844" related-article-type="in-this-issue" vol="372">844</jats:related-article> </jats:p>

<jats:title>A complex role for chlorine radicals</jats:title> <jats:p> Radicals are atoms or molecules that are highly reactive because they have an unpaired electron. A common means of investigating whether they are involved in a particular reaction is to try to trap them with an acceptor compound. Yang <jats:italic>et al.</jats:italic> reinvestigated a photoinduced alkane oxidation reaction for which a trapping study had previously implicated alkoxy radicals. Their spectroscopic, kinetic, and isotopic labeling studies revealed that chlorine, rather than alkoxy, was the key radical intermediate; the prior trapping results had stemmed from its complexation with alcohols. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abd8408, this issue p. <jats:related-article issue="6544" page="847" related-article-type="in-this-issue" vol="372">847</jats:related-article> </jats:p>

<jats:p>The quest for planar sp<jats:sup>2</jats:sup>-hybridized carbon allotropes other than graphene, such as graphenylene and biphenylene networks, has stimulated substantial research efforts because of the materials’ predicted mechanical, electronic, and transport properties. However, their syntheses remain challenging given the lack of reliable protocols for generating nonhexagonal rings during the in-plane tiling of carbon atoms. We report the bottom-up growth of an ultraflat biphenylene network with periodically arranged four-, six-, and eight-membered rings of sp<jats:sup>2</jats:sup>-hybridized carbon atoms through an on-surface interpolymer dehydrofluorination (HF-zipping) reaction. The characterization of this biphenylene network by scanning probe methods reveals that it is metallic rather than a dielectric. We expect the interpolymer HF-zipping method to complement the toolbox for the synthesis of other nonbenzenoid carbon allotropes.</jats:p>