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71.
Translocation of lipid-linked oligosaccharides across the ER membrane requires Rft1 protein. 总被引:6,自引:0,他引:6
Jonne Helenius Davis T W Ng Cristina L Marolda Peter Walter Miguel A Valvano Markus Aebi 《Nature》2002,415(6870):447-450
N-linked glycosylation of proteins in eukaryotic cells follows a highly conserved pathway. The tetradecasaccharide substrate (Glc3Man9GlcNAc2) is first assembled at the membrane of the endoplasmic reticulum (ER) as a dolichylpyrophosphate (Dol-PP)-linked intermediate, and then transferred to nascent polypeptide chains in the lumen of the ER. The assembly of the oligosaccharide starts on the cytoplasmic side of the ER membrane with the synthesis of a Man5GlcNAc2-PP-Dol intermediate. This lipid-linked intermediate is then translocated across the membrane so that the oligosaccharides face the lumen of the ER, where the biosynthesis of Glc3Man9GlcNAc2-PP-Dol continues to completion. The fully assembled oligosaccharide is transferred to selected asparagine residues of target proteins. The transmembrane movement of lipid-linked Man5GlcNAc2 oligosaccharide is of fundamental importance in this biosynthetic pathway, and similar processes involving phospholipids and glycolipids are essential in all types of cells. The process is predicted to be catalysed by proteins, termed flippases, which to date have remained elusive. Here we provide evidence that yeast RFT1 encodes an evolutionarily conserved protein required for the translocation of Man5GlcNAc2-PP-Dol from the cytoplasmic to the lumenal leaflet of the ER membrane. 相似文献
72.
In leukocytes (PMN) of individuals with Swiss type acatalasemia, the rate of dehydroascorbate reduction is 4 times normal. This observation suggests that the protective function served by catalase in human PMN is supported by dehydroascorbate reductase. 相似文献
73.
Changing boreal methane sources and constant biomass burning during the last termination 总被引:2,自引:0,他引:2
Fischer H Behrens M Bock M Richter U Schmitt J Loulergue L Chappellaz J Spahni R Blunier T Leuenberger M Stocker TF 《Nature》2008,452(7189):864-867
Past atmospheric methane concentrations show strong fluctuations in parallel to rapid glacial climate changes in the Northern Hemisphere superimposed on a glacial-interglacial doubling of methane concentrations. The processes driving the observed fluctuations remain uncertain but can be constrained using methane isotopic information from ice cores. Here we present an ice core record of carbon isotopic ratios in methane over the entire last glacial-interglacial transition. Our data show that the carbon in atmospheric methane was isotopically much heavier in cold climate periods. With the help of a box model constrained by the present data and previously published results, we are able to estimate the magnitude of past individual methane emission sources and the atmospheric lifetime of methane. We find that methane emissions due to biomass burning were about 45 Tg methane per year, and that these remained roughly constant throughout the glacial termination. The atmospheric lifetime of methane is reduced during cold climate periods. We also show that boreal wetlands are an important source of methane during warm events, but their methane emissions are essentially shut down during cold climate conditions. 相似文献
74.
Lämmermann T Bader BL Monkley SJ Worbs T Wedlich-Söldner R Hirsch K Keller M Förster R Critchley DR Fässler R Sixt M 《Nature》2008,453(7191):51-55
All metazoan cells carry transmembrane receptors of the integrin family, which couple the contractile force of the actomyosin cytoskeleton to the extracellular environment. In agreement with this principle, rapidly migrating leukocytes use integrin-mediated adhesion when moving over two-dimensional surfaces. As migration on two-dimensional substrates naturally overemphasizes the role of adhesion, the contribution of integrins during three-dimensional movement of leukocytes within tissues has remained controversial. We studied the interplay between adhesive, contractile and protrusive forces during interstitial leukocyte chemotaxis in vivo and in vitro. We ablated all integrin heterodimers from murine leukocytes, and show here that functional integrins do not contribute to migration in three-dimensional environments. Instead, these cells migrate by the sole force of actin-network expansion, which promotes protrusive flowing of the leading edge. Myosin II-dependent contraction is only required on passage through narrow gaps, where a squeezing contraction of the trailing edge propels the rigid nucleus. 相似文献
75.
76.
Bottom-up effects of plant diversity on multitrophic interactions in a biodiversity experiment 总被引:2,自引:0,他引:2
Scherber C Eisenhauer N Weisser WW Schmid B Voigt W Fischer M Schulze ED Roscher C Weigelt A Allan E Bessler H Bonkowski M Buchmann N Buscot F Clement LW Ebeling A Engels C Halle S Kertscher I Klein AM Koller R König S Kowalski E Kummer V Kuu A Lange M Lauterbach D Middelhoff C Migunova VD Milcu A Müller R Partsch S Petermann JS Renker C Rottstock T Sabais A Scheu S Schumacher J Temperton VM Tscharntke T 《Nature》2010,468(7323):553-556
Biodiversity is rapidly declining, and this may negatively affect ecosystem processes, including economically important ecosystem services. Previous studies have shown that biodiversity has positive effects on organisms and processes across trophic levels. However, only a few studies have so far incorporated an explicit food-web perspective. In an eight-year biodiversity experiment, we studied an unprecedented range of above- and below-ground organisms and multitrophic interactions. A multitrophic data set originating from a single long-term experiment allows mechanistic insights that would not be gained from meta-analysis of different experiments. Here we show that plant diversity effects dampen with increasing trophic level and degree of omnivory. This was true both for abundance and species richness of organisms. Furthermore, we present comprehensive above-ground/below-ground biodiversity food webs. Both above ground and below ground, herbivores responded more strongly to changes in plant diversity than did carnivores or omnivores. Density and richness of carnivorous taxa was independent of vegetation structure. Below-ground responses to plant diversity were consistently weaker than above-ground responses. Responses to increasing plant diversity were generally positive, but were negative for biological invasion, pathogen infestation and hyperparasitism. Our results suggest that plant diversity has strong bottom-up effects on multitrophic interaction networks, with particularly strong effects on lower trophic levels. Effects on higher trophic levels are indirectly mediated through bottom-up trophic cascades. 相似文献
77.
Recent decline in the global land evapotranspiration trend due to limited moisture supply 总被引:31,自引:0,他引:31
Jung M Reichstein M Ciais P Seneviratne SI Sheffield J Goulden ML Bonan G Cescatti A Chen J de Jeu R Dolman AJ Eugster W Gerten D Gianelle D Gobron N Heinke J Kimball J Law BE Montagnani L Mu Q Mueller B Oleson K Papale D Richardson AD Roupsard O Running S Tomelleri E Viovy N Weber U Williams C Wood E Zaehle S Zhang K 《Nature》2010,467(7318):951-954
More than half of the solar energy absorbed by land surfaces is currently used to evaporate water. Climate change is expected to intensify the hydrological cycle and to alter evapotranspiration, with implications for ecosystem services and feedback to regional and global climate. Evapotranspiration changes may already be under way, but direct observational constraints are lacking at the global scale. Until such evidence is available, changes in the water cycle on land?a key diagnostic criterion of the effects of climate change and variability?remain uncertain. Here we provide a data-driven estimate of global land evapotranspiration from 1982 to 2008, compiled using a global monitoring network, meteorological and remote-sensing observations, and a machine-learning algorithm. In addition, we have assessed evapotranspiration variations over the same time period using an ensemble of process-based land-surface models. Our results suggest that global annual evapotranspiration increased on average by 7.1?±?1.0?millimetres per year per decade from 1982 to 1997. After that, coincident with the last major El Ni?o event in 1998, the global evapotranspiration increase seems to have ceased until 2008. This change was driven primarily by moisture limitation in the Southern Hemisphere, particularly Africa and Australia. In these regions, microwave satellite observations indicate that soil moisture decreased from 1998 to 2008. Hence, increasing soil-moisture limitations on evapotranspiration largely explain the recent decline of the global land-evapotranspiration trend. Whether the changing behaviour of evapotranspiration is representative of natural climate variability or reflects a more permanent reorganization of the land water cycle is a key question for earth system science. 相似文献
78.
Markus Thamm Sabine Balfanz Ricarda Scheiner Arnd Baumann Wolfgang Blenau 《Cellular and molecular life sciences : CMLS》2010,67(14):2467-2479
Serotonin plays a key role in modulating various physiological and behavioral processes in both protostomes and deuterostomes.
The vast majority of serotonin receptors belong to the superfamily of G-protein-coupled receptors. We report the cloning of
a cDNA from the honeybee (Am5-ht1A) sharing high similarity with members of the 5-HT1 receptor class. Activation of Am5-HT1A by serotonin inhibited the production of cAMP in a dose-dependent manner (EC50 = 16.9 nM). Am5-HT1A was highly expressed in brain regions known to be involved in visual information processing. Using in vivo pharmacology,
we could demonstrate that Am5-HT1A receptor ligands had a strong impact on the phototactic behavior of individual bees. The data presented here mark the first
comprehensive study—from gene to behavior—of a 5-HT1A receptor in the honeybee, paving the way for the eventual elucidation of additional roles of this receptor subtype in the
physiology and behavior of this social insect. 相似文献
79.
Chiow KH Tan Y Chua RY Huang D Ng ML Torta F Wenk MR Wong SH 《Cellular and molecular life sciences : CMLS》2012,69(9):1505-1521
Since being introduced globally as aspirin in 1899, acetylsalicylic acid has been widely used as an analgesic, anti-inflammation,
anti-pyretic, and anti-thrombotic drug for years. Aspirin had been reported to down-regulate surface expression of CD40, CD80,
CD86, and MHCII in myeloid dendritic cells (DC), which played essential roles in regulating the immune system. We hypothesized
that the down-regulation of these surface membrane proteins is partly due to the ability of aspirin in regulating trafficking/sorting
of endocytosed surface membrane proteins. By using an established epidermoid carcinoma cell line (A-431), which overexpresses
the epidermal growth factor receptor (EGFR) and transferrin receptor (TfnR), we show that aspirin (1) reduces cell surface
expression of EGFR and (2) accumulates endocytosed-EGFR and -TfnR in the early/sorting endosome (ESE). Further elucidation
of the mechanism suggests that aspirin enhances recruitment of SNX3 and SNX5 to membranes and consistently, both SNX3 and
SNX5 play essential roles in the aspirin-mediated accumulation of endocytosed-TfnR at the ESE. This study sheds light on how
aspirin may down-regulate surface expression of EGFR by inhibiting/delaying the exit of endocytosed-EGFR from the ESE and
recycling of endocytosed-EGFR back to the cell surface. 相似文献
80.
Genome-wide association study identifies multiple loci influencing human serum metabolite levels 总被引:1,自引:0,他引:1
Kettunen J Tukiainen T Sarin AP Ortega-Alonso A Tikkanen E Lyytikäinen LP Kangas AJ Soininen P Würtz P Silander K Dick DM Rose RJ Savolainen MJ Viikari J Kähönen M Lehtimäki T Pietiläinen KH Inouye M McCarthy MI Jula A Eriksson J Raitakari OT Salomaa V Kaprio J Järvelin MR Peltonen L Perola M Freimer NB Ala-Korpela M Palotie A Ripatti S 《Nature genetics》2012,44(3):269-276
Nuclear magnetic resonance assays allow for measurement of a wide range of metabolic phenotypes. We report here the results of a GWAS on 8,330 Finnish individuals genotyped and imputed at 7.7 million SNPs for a range of 216 serum metabolic phenotypes assessed by NMR of serum samples. We identified significant associations (P < 2.31 × 10(-10)) at 31 loci, including 11 for which there have not been previous reports of associations to a metabolic trait or disorder. Analyses of Finnish twin pairs suggested that the metabolic measures reported here show higher heritability than comparable conventional metabolic phenotypes. In accordance with our expectations, SNPs at the 31 loci associated with individual metabolites account for a greater proportion of the genetic component of trait variance (up to 40%) than is typically observed for conventional serum metabolic phenotypes. The identification of such associations may provide substantial insight into cardiometabolic disorders. 相似文献