Catálogo de publicaciones - revistas

<jats:p>Liu <jats:italic>et al</jats:italic>. (Research Articles, 13 October 2017) inferred carbon flux anomalies in tropical continents with enough confidence to constrain the driving carbon-exchange processes. I show that they underestimated their error budget and that more effort must be invested in the satellite concentration retrievals and in the atmospheric transport models before such precision can be achieved.</jats:p>

<jats:p>In bacteria, nascent proteins bear the pretranslationally generated N-terminal (Nt) formyl-methionine (fMet) residue. Nt-fMet of bacterial proteins is a degradation signal, termed fMet/N-degron. By contrast, proteins synthesized by cytosolic ribosomes of eukaryotes were presumed to bear unformylated Nt-Met. Here we found that the yeast formyltransferase Fmt1, although imported into mitochondria, could also produce Nt-formylated proteins in the cytosol. Nt-formylated proteins were strongly up-regulated in stationary phase or upon starvation for specific amino acids. This up-regulation strictly required the Gcn2 kinase, which phosphorylates Fmt1 and mediates its retention in the cytosol. We also found that the Nt-fMet residues of Nt-formylated proteins act as fMet/N-degrons and identified the Psh1 ubiquitin ligase as the recognition component of the eukaryotic fMet/N-end rule pathway, which destroys Nt-formylated proteins.</jats:p>

<jats:p>Chevallier showed a column CO<jats:sub>2</jats:sub> (<jats:inline-formula><m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"><m:mrow><m:msub><m:mi mathvariant="normal">X</m:mi><m:mrow><m:msub><m:mrow><m:mi mathvariant="normal">CO</m:mi></m:mrow><m:mn>2</m:mn></m:msub></m:mrow></m:msub></m:mrow></m:math></jats:inline-formula>) anomaly of ±0.5 parts per million forced by a uniform net biosphere exchange (NBE) anomaly of 2.5 gigatonnes of carbon over the tropical continents within a year, so he claimed that the inferred NBE uncertainties should be larger than presented in Liu <jats:italic>et al</jats:italic>. We show that a much concentrated NBE anomaly led to much larger <jats:inline-formula><m:math xmlns:m="http://www.w3.org/1998/Math/MathML" overflow="scroll"><m:mrow><m:msub><m:mi mathvariant="normal">X</m:mi><m:mrow><m:msub><m:mrow><m:mi mathvariant="normal">CO</m:mi></m:mrow><m:mn>2</m:mn></m:msub></m:mrow></m:msub></m:mrow></m:math></jats:inline-formula> perturbations.</jats:p>

<jats:p>We report a 3.5-angstrom-resolution cryo–electron microscopy structure of a respiratory supercomplex isolated from <jats:italic>Mycobacterium smegmatis.</jats:italic> It comprises a complex III dimer flanked on either side by individual complex IV subunits. Complex III and IV associate so that electrons can be transferred from quinol in complex III to the oxygen reduction center in complex IV by way of a bridging cytochrome subunit. We observed a superoxide dismutase-like subunit at the periplasmic face, which may be responsible for detoxification of superoxide formed by complex III. The structure reveals features of an established drug target and provides a foundation for the development of treatments for human tuberculosis.</jats:p>

<jats:p>An imbalance in the colonic microbiota might underlie many human diseases, but the mechanisms that maintain homeostasis remain elusive. Recent insights suggest that colonocyte metabolism functions as a control switch, mediating a shift between homeostatic and dysbiotic communities. During homeostasis, colonocyte metabolism is directed toward oxidative phosphorylation, resulting in high epithelial oxygen consumption. The consequent epithelial hypoxia helps to maintain a microbial community dominated by obligate anaerobic bacteria, which provide benefit by converting fiber into fermentation products absorbed by the host. Conditions that alter the metabolism of the colonic epithelium increase epithelial oxygenation, thereby driving an expansion of facultative anaerobic bacteria, a hallmark of dysbiosis in the colon. Enteric pathogens subvert colonocyte metabolism to escape niche protection conferred by the gut microbiota. The reverse strategy, a metabolic reprogramming to restore colonocyte hypoxia, represents a promising new therapeutic approach for rebalancing the colonic microbiota in a broad spectrum of human diseases.</jats:p>

<jats:p>The 26<jats:italic>S</jats:italic> proteasome is the primary eukaryotic degradation machine and thus is critically involved in numerous cellular processes. The heterohexameric adenosine triphosphatase (ATPase) motor of the proteasome unfolds and translocates targeted protein substrates into the open gate of a proteolytic core while a proteasomal deubiquitinase concomitantly removes substrate-attached ubiquitin chains. However, the mechanisms by which ATP hydrolysis drives the conformational changes responsible for these processes have remained elusive. Here we present the cryo–electron microscopy structures of four distinct conformational states of the actively ATP-hydrolyzing, substrate-engaged 26<jats:italic>S</jats:italic> proteasome. These structures reveal how mechanical substrate translocation accelerates deubiquitination and how ATP-binding, -hydrolysis, and phosphate-release events are coordinated within the AAA+ (ATPases associated with diverse cellular activities) motor to induce conformational changes and propel the substrate through the central pore.</jats:p>