Catálogo de publicaciones - revistas

<jats:title>Remember the sugar when making proteins</jats:title> <jats:p> Eukaryotes have an elaborate trafficking and quality-control system for secreted glycoproteins. The glycosylation pathway begins in the endoplasmic reticulum with the enzyme oligosaccharyltransferase (OST), which attaches a long chain of sugars to asparagine residues of target proteins. Wild <jats:italic>et al.</jats:italic> report a cryo-electron microscopy structure of yeast OST, which includes eight separate membrane proteins. The central catalytic subunit contains binding sites for substrates and is flanked by accessory subunits that may facilitate delivery of newly translocated proteins for glycosylation. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="545" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar5140">545</jats:related-article> </jats:p>

<jats:title>Brain mutations, young and old</jats:title> <jats:p> Most neurons that make up the human brain are postmitotic, living and functioning for a very long time without renewal (see the Perspective by Lee). Bae <jats:italic>et al.</jats:italic> examined the genomes of single neurons from the prenatal developing human brain. Both the type of mutation and the rates of accumulation changed between gastrulation and neurogenesis. These early mutations could be generating useful neuronal diversity or could predispose individuals to later dysfunction. Lodato <jats:italic>et al.</jats:italic> also found that neurons take on somatic mutations as they age by sequencing single neurons from subjects aged 4 months to 82 years. Somatic mutations accumulated with increasing age and accumulated faster in individuals affected by inborn errors in DNA repair. Postmitotic mutations might only affect one neuron, but the accumulated divergence of genomes across the brain could affect function. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="550" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aan8690">550</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="555" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aao4426">555</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="521" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar6335">521</jats:related-article> </jats:p>

<jats:title>Brain mutations, young and old</jats:title> <jats:p> Most neurons that make up the human brain are postmitotic, living and functioning for a very long time without renewal (see the Perspective by Lee). Bae <jats:italic>et al.</jats:italic> examined the genomes of single neurons from the prenatal developing human brain. Both the type of mutation and the rates of accumulation changed between gastrulation and neurogenesis. These early mutations could be generating useful neuronal diversity or could predispose individuals to later dysfunction. Lodato <jats:italic>et al.</jats:italic> also found that neurons take on somatic mutations as they age by sequencing single neurons from subjects aged 4 months to 82 years. Somatic mutations accumulated with increasing age and accumulated faster in individuals affected by inborn errors in DNA repair. Postmitotic mutations might only affect one neuron, but the accumulated divergence of genomes across the brain could affect function. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="550" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aan8690">550</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="555" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aao4426">555</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="521" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar6335">521</jats:related-article> </jats:p>

<jats:title>About-face for citrate synthase</jats:title> <jats:p> Classically, it is thought that citrate synthase only works in one direction: to catalyze the production of citrate from acetyl coenzyme A and oxaloacetate in the tricarboxylic acid (TCA) cycle. The TCA cycle can run in reverse to cleave citrate and fix carbon dioxide autotrophically, but this was thought to occur only with alternative enzymes, such as citrate lyase. Now Nunoura <jats:italic>et al.</jats:italic> and Mall <jats:italic>et al.</jats:italic> have discovered thermophilic bacteria with highly efficient and reversible citrate synthase that requires reduced ferredoxin (see the Perspective by Ragsdale). This function is undetectable by metagenomics, but classical biochemistry filled in the gaps seen between the genome sequences and the phenotypes of the organisms. The direction of catalysis depends on the availability of organic versus inorganic carbon and reflects a flexible bet-hedging strategy for survival in fluctuating environments. In evolutionary terms, this capacity might predate the classical TCA cycle and is likely to occur in a wide range of anaerobic microorganisms. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="559" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aao3407">559</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="563" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aao2410">563</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="517" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar6329">517</jats:related-article> </jats:p>

<jats:title>About-face for citrate synthase</jats:title> <jats:p> Classically, it is thought that citrate synthase only works in one direction: to catalyze the production of citrate from acetyl coenzyme A and oxaloacetate in the tricarboxylic acid (TCA) cycle. The TCA cycle can run in reverse to cleave citrate and fix carbon dioxide autotrophically, but this was thought to occur only with alternative enzymes, such as citrate lyase. Now Nunoura <jats:italic>et al.</jats:italic> and Mall <jats:italic>et al.</jats:italic> have discovered thermophilic bacteria with highly efficient and reversible citrate synthase that requires reduced ferredoxin (see the Perspective by Ragsdale). This function is undetectable by metagenomics, but classical biochemistry filled in the gaps seen between the genome sequences and the phenotypes of the organisms. The direction of catalysis depends on the availability of organic versus inorganic carbon and reflects a flexible bet-hedging strategy for survival in fluctuating environments. In evolutionary terms, this capacity might predate the classical TCA cycle and is likely to occur in a wide range of anaerobic microorganisms. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="559" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aao3407">559</jats:related-article> , p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="563" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aao2410">563</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="517" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar6329">517</jats:related-article> </jats:p>

<jats:title>A demanding lifestyle</jats:title> <jats:p> Polar bears appear to be well adapted to the extreme conditions of their Arctic habitat. Pagano <jats:italic>et al.</jats:italic> , however, show that the energy balance in this harsh environment is narrower than we might expect (see the Perspective by Whiteman). They monitored the behavior and metabolic rates of nine free-ranging polar bears over 2 years. They found that high energy demands required consumption of high-fat prey, such as seals, which are easy to come by on sea ice but nearly unavailable in ice-free conditions. Thus, as sea ice becomes increasingly short-lived annually, polar bears are likely to experience increasingly stressful conditions and higher mortality rates. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="568" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aan8677">568</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="514" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar6723">514</jats:related-article> </jats:p>

<jats:title>Compensating a polar surface</jats:title> <jats:p> An ionic crystal surface can be electrostatically unstable, and the surface must reconstruct in some way to avoid this “polar catastrophe.” Setvin <jats:italic>et al.</jats:italic> used scanning probe microscopies and density functional theory to study the changes in the polar surface of the perovskite KTaO <jats:sub>3</jats:sub> . They observed several structural reconstructions as the surface cleaved in vacuum was heated to higher temperatures. These ranged from surface distortions to the formation of oxygen vacancies to the development of KO and TaO <jats:sub>2</jats:sub> stripes. Hydroxylation after exposure to water vapor also stabilized the surface. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="572" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar2287">572</jats:related-article> </jats:p>

<jats:title>A nonlinear peek into stripes</jats:title> <jats:p> In many theoretical models of high-temperature superconductors, remnants of superconductivity persist to temperatures higher than the transition temperature, <jats:italic>T</jats:italic> <jats:sub>C</jats:sub> . Rajasekaran <jats:italic>et al.</jats:italic> used nonlinear terahertz spectroscopy to probe this region of the phase diagram of a cuprate superconductor that is well known for a stripe phase that appears for certain doping levels (see the Perspective by Ergeçen and Gedik). For a sample deep in the stripe phase, a large nonlinear signal persisted from the superconducting region up to temperatures much higher than <jats:italic>T</jats:italic> <jats:sub>C</jats:sub> . The findings suggest the formation of a peculiar spatially modulated superconducting state called the pair-density wave. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="575" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aan3438">575</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="519" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar5254">519</jats:related-article> </jats:p>

<jats:title>A phonon merry-go-round</jats:title> <jats:p> Chirality is associated with the breaking of symmetry, often described as left- or right-handed behavior. Such asymmetry can be seen, for example, in the electronic responses of particular materials or the reactions between particular chemical species. Zhu <jats:italic>et al.</jats:italic> observed a chiral phonon mode in a monolayer of the transition metal dichalcogenide WSe <jats:sub>2</jats:sub> , detected spectroscopically as the circular dichroism of the phonon-assisted transition of holes. Phonon chirality could be used to control the electron-phonon coupling and/or the phonon-driven topological states of solids. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="579" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar2711">579</jats:related-article> </jats:p>

<jats:title>HLA genotype affects response</jats:title> <jats:p> Immunotherapy works by activating the patient's own immune system to fight cancer. For effective tumor killing, CD8 <jats:sup>+</jats:sup> T cells recognize tumor peptides presented by human leukocyte antigen class I (HLA-I) molecules. In humans, there are three major HLA-I genes ( <jats:italic>HLA-A, HLA-B</jats:italic> , and <jats:italic>HLA-C</jats:italic> ). Chowell <jats:italic>et al.</jats:italic> asked whether germline HLA-I genotype influences how T cells recognize tumor peptides and respond to checkpoint inhibitor immunotherapies (see the Perspective by Kvistborg and Yewdell). They examined more than 1500 patients and found that heterozygosity at HLA-I loci was associated with better survival than homozygosity for one or more HLA-I genes. Thus, specific HLA-I mutations could have implications for immune recognition and for the design of epitopes for cancer vaccines and immunotherapies. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="582" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aao4572">582</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6375" page="516" related-article-type="in-this-issue" vol="359" xlink:href="10.1126/science.aar6574">516</jats:related-article> </jats:p>