323 research outputs found
Biosynthesis of Selenocysteine on Its tRNA in Eukaryotes
Selenocysteine (Sec) is cotranslationally inserted into protein in response to UGA codons and is the 21st amino acid in the genetic code. However, the means by which Sec is synthesized in eukaryotes is not known. Herein, comparative genomics and experimental analyses revealed that the mammalian Sec synthase (SecS) is the previously identified pyridoxal phosphate-containing protein known as the soluble liver antigen. SecS required selenophosphate and O-phosphoseryl-tRNA([Ser]Sec) as substrates to generate selenocysteyl-tRNA([Ser]Sec). Moreover, it was found that Sec was synthesized on the tRNA scaffold from selenide, ATP, and serine using tRNA([Ser]Sec), seryl-tRNA synthetase, O-phosphoseryl-tRNA([Ser]Sec) kinase, selenophosphate synthetase, and SecS. By identifying the pathway of Sec biosynthesis in mammals, this study not only functionally characterized SecS but also assigned the function of the O-phosphoseryl-tRNA([Ser]Sec) kinase. In addition, we found that selenophosphate synthetase 2 could synthesize monoselenophosphate in vitro but selenophosphate synthetase 1 could not. Conservation of the overall pathway of Sec biosynthesis suggests that this pathway is also active in other eukaryotes and archaea that synthesize selenoproteins
Inter-annual growth of Arctic charr (Salvelinus alpinus, L.) in relation to climate variation
BACKGROUND: Major changes in climate have been observed in the Arctic and climate models predict further amplification of the enhanced greenhouse effect at high-latitudes leading to increased warming. We propose that warming in the Arctic may affect the annual growth conditions of the cold adapted Arctic charr and that such effects can already be detected retrospectrally using otolith data. RESULTS: Inter-annual growth of the circumpolar Arctic charr (Salvelinus alpinus, L.) was analysed in relation to climatic changes observed in the Arctic during the last two decades. Arctic charr were sampled from six locations at Qeqertarsuaq in West Greenland, where climate data have been recorded since 1990. Two fish populations met the criteria of homogeny and, consequently, only these were used in further analyses. The results demonstrate a complex coupling between annual growth rates and fluctuations in annual mean temperatures and precipitation. Significant changes in temporal patterns of growth were observed between cohorts of 1990 and 2004. CONCLUSION: Differences in pattern of growth appear to be a consequence of climatic changes over the last two decades and we thereby conclude that climatic affects short term and inter-annual growth as well as influencing long term shifts in age-specific growth patterns in population of Arctic charr
Increasing Incidence of Hospitalization for Stroke and Transient Ischemic Attack in Young Adults:A Registry-Based Study
BACKGROUND: Studies have reported increasing incidence of ischemic stroke in adults younger than 50 to 55 years. Information on temporal trends of other stroke subtypes and transient ischemic attack (TIA) is sparse. The aim of this study was to investigate temporal trends of the incidence of hospitalizations for TIA and stroke including sexâ and subtypeâspecific trends in young adults aged 15 to 30Â years. METHODS AND RESULTS: From the Danish National Patient Register, we identified all cases of firstâever stroke and TIA (age 15â30Â years) in Denmark, who were hospitalized during the study period of 1994 to 2012. Incidence rates and estimated annual percentage changes (EAPCs) were estimated by using Poisson regression. During the study period, 4156 cases of firstâever hospitalization for stroke/TIA were identified. The ageâstandardized incidence rates of hospitalizations for stroke increased significantly (EAPC 1.83% [95% CI 1.11â2.55%]) from 11.97/100Â 000Â personâyears (PY) in 1994 to 16.77/100Â 000Â PY in 2012. TIA hospitalizations increased from 1.93/100Â 000Â PY in 1994 to 5.81/100Â 000Â PY in 2012 and after 2006 more markedly in men than in women (EAPC 16.61% [95% CI 10.45â23.12%]). The incidence of hospitalizations for ischemic stroke was markedly lower among men, but increased significantly from 2006 (EAPC 14.60% [95% CI 6.22â23.63%]). The incidences of hospitalizations for intracerebral hemorrhage and subarachnoid hemorrhage remained stable during the study period. CONCLUSIONS: The incidence rates of firstâtime hospitalizations for ischemic stroke and TIA in young Danish adults have increased substantially since the mid 1990s. The increase was particularly prominent in the most recent years
Mutational Analysis of the Cyanobacterial Nitrogen Regulator PipX
PipX provides a functional link between the cyanobacterial global transcriptional regulator NtcA and the signal transduction protein PII, a protein found in all three domains of life as integrators of signals of the nitrogen and carbon balance. PipX, which is toxic in the absence of PII, can form alternative complexes with NtcA and PII and these interactions are respectively stimulated and inhibited by 2-oxoglutarate, providing a mechanism by which PII can modulate expression at the NtcA regulon. Structural information on PipX-NtcA complexes suggests that PipX coactivates NtcA controlled genes by stabilizing the active conformation of NtcA bound to 2-oxoglutarate and by possibly helping recruit RNA polymerase. To get insights into PipX functions, we perform here a mutational analysis of pipX informed by the structures of PipX-PII and PipX-NtcA complexes and evaluate the impact of point mutations on toxicity and gene expression. Two amino acid substitutions (Y32A and E4A) were of particular interest, since they increased PipX toxicity and activated NtcA dependent genes in vivo at lower 2-oxoglutarate levels than wild type PipX. While both mutations impaired complex formation with PII, only Y32A had a negative impact on PipX-NtcA interactions
The marine reservoir age of Greenland coastal waters
Knowledge of the marine reservoir age is fundamental for creating reliable chronologies of marine sediment archives based on radiocarbon dating. This age difference between the 14C age of a marine sample and that of its contemporaneous atmosphere is dependent on several factors (among others, ocean circulation, water mass distribution, terrestrial runoff, upwelling, and sea-ice cover) and is therefore spatially heterogeneous. Anthropogenic influence on the global isotopic carbon system, mostly through atmospheric nuclear tests, has complicated the determination of the regional reservoir age correction ÎR, which therefore can only be measured in historic samples of known age. In this study we expand on the few existing measurements of ÎR for the coastal waters around Greenland, by adding 92 new radiocarbon dates on mollusks from museum collections. All studied mollusk samples were collected during historic expeditions of the late 19th and early 20th centuries, and besides coastal sites around Greenland, the new measurements also include localities from the western Labrador Sea, Baffin Bay, and the Iceland Sea. Together with existing measurements, the new results are used to calculate average ÎR values for different regions around Greenland, all in relation to Marine20, the most recent marine radiocarbon calibration curve. To support further discussions and comparison with previous datasets, we use the term ÎR13, where the suffix 13 refers to the previous calibration curve Marine13. Our study explores the links between the marine reservoir age and oceanography, sea-ice cover, water depth, mollusk feeding habits, and the presence of carbonate bedrock. Although we provide regional averages, we encourage people to consult the full catalogue of measurements and determine a suitable ÎR for each case individually, based on the exact location including water depth. Despite this significant expansion of the regional reservoir age database around Greenland, data from the northern coast, directly bordering the Arctic Ocean, remain missing.</p
Mechanism of Disruption of the Amt-GlnK Complex by PII-Mediated Sensing of 2-Oxoglutarate
GlnK proteins regulate the active uptake of ammonium by Amt transport proteins by inserting their regulatory T-loops into the transport channels of the Amt trimer and physically blocking substrate passage. They sense the cellular nitrogen status through 2-oxoglutarate, and the energy level of the cell by binding both ATP and ADP with different affinities. The hyperthermophilic euryarchaeon Archaeoglobus fulgidus possesses three Amt proteins, each encoded in an operon with a GlnK ortholog. One of these proteins, GlnK2 was recently found to be incapable of binding 2-OG, and in order to understand the implications of this finding we conducted a detailed structural and functional analysis of a second GlnK protein from A. fulgidus, GlnK3. Contrary to Af-GlnK2 this protein was able to bind both ATP/2-OG and ADP to yield inactive and functional states, respectively. Due to the thermostable nature of the protein we could observe the exact positioning of the notoriously flexible T-loops and explain the binding behavior of GlnK proteins to their interaction partner, the Amt proteins. A thermodynamic analysis of these binding events using microcalorimetry evaluated by microstate modeling revealed significant differences in binding cooperativity compared to other characterized PII proteins, underlining the diversity and adaptability of this class of regulatory signaling proteins
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