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  • Hauryliuk, Vasili, et al. (författare)
  • The pretranslocation ribosome is targeted by GTP-bound EF-G in partially activated form.
  • 2008
  • Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - 0027-8424 .- 1091-6490. ; 105:41, s. 15678-83
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>Translocation of the tRNA x mRNA complex through the bacterial ribosome is driven by the multidomain guanosine triphosphatase elongation factor G (EF-G). We have used isothermal titration calorimetry to characterize the binding of GDP and GTP to free EF-G at 4 degrees C, 20 degrees C, and 37 degrees C. The binding affinity of EF-G is higher to GDP than to GTP at 4 degrees C, but lower at 37 degrees C. The binding enthalpy and entropy change little with temperature in the case of GDP binding but change greatly in the case of GTP binding. These observations are compatible with a large decrease in the solvent-accessible hydrophobic surface area of EF-G on GTP, but not GDP, binding. The explanation we propose is the locking of the switch 1 and switch 2 peptide loops in the G domain of EF-G to the gamma-phosphate of GTP. From these data, in conjunction with previously reported structural data on guanine nucleotide-bound EF-G, we suggest that EF-G enters the pretranslocation ribosome as an "activity chimera," with the G domain activated by the presence of GTP but the overall factor conformation in the inactive form typical of a GDP-bound multidomain guanosine triphosphatase. We propose that the active overall conformation of EF-G is attained only in complex with the ribosome in its "ratcheted state," with hybrid tRNA binding sites.</p>
  • Hauryliuk, Vasili, et al. (författare)
  • Thermodynamics of GTP and GDP Binding to Bacterial Initiation Factor 2 Suggests Two Types of Structural Transitions
  • 2009
  • Ingår i: Journal of Molecular Biology. - 0022-2836 .- 1089-8638. ; 394:4, s. 621-626
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>During initiation of messenger RNA translation in bacteria, the GTPase initiation factor (IF) 2 plays major roles in the assembly of the preinitiation 30S complex and its docking to the 50S ribosomal subunit leading to the 70S initiation complex, ready to form the first peptide bond in a nascent protein. Rapid and accurate initiation of bacterial protein synthesis is driven by conformational changes in IF2, induced by GDP-GTP exchange and GTP hydrolysis. We have used isothermal titration calorimetry and linear extrapolation to characterize the thermodynamics of the binding of GDP and GTP to free IF2 in the temperature interval 4-37 degrees C. IF2 binds with about 20-fold and 2-fold higher affinity for GDP than for GTP at 4 and 37 degrees C, respectively. The binding of IF2 to both GTP and GDP is characterized by a large heat capacity change (-868 +/- 25 and -577 +/- 23 cal mol(-1) K-1, respectively), associated with compensatory changes in binding entropy and enthalpy. From our data, we propose that GTP binding to IF2 leads to protection of hydrophobic amino acid residues from solvent by the locking of switch I and switch H loops to the gamma-phosphate of GTP, as in the case of elongation factor G. From the large heat capacity change (also upon GDP binding) not seen in the case of elongation factor G, we propose the existence of yet another type of conformational change in IF2, which is induced by GDP and GTP alike. Also, this transition is likely to protect hydrophobic groups from solvent, and its functional relevance is discussed. (C) 2009 Elsevier Ltd. All rights reserved.</p>
  • Mitkevich, Vladimir A., et al. (författare)
  • Thermodynamic Characterization of ppGpp Binding to EF-G or 1F2 and of Initiator tRNA Binding to Free 1F2 in the Presence of GDP, GTP, or ppGpp
  • 2010
  • Ingår i: Journal of Molecular Biology. - 0022-2836 .- 1089-8638. ; 402:5, s. 838-846
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>In addition to their natural substrates GDP and GTP, the bacterial translational GTPases initiation factor (IF) 2 and elongation factor G (EF-G) interact with the alarmone molecule guanosine tetraphosphate (ppGpp), which leads to GTPase inhibition. We have used isothermal titration calorimetry to determine the affinities of ppGpp for IF2 and EF-G at a temperature interval of 5-25 degrees C. We find that ppGpp has a higher affinity for IF2 than for EF-G (1.7-2.8 Q mu M K-d versus 9.1-13.9 mu M K-d at 10-25 degrees C), suggesting that during stringent response in vivo, IF2 is more responsive to ppGpp than to EF-G. We investigated the effects of ppGpp, GDP, and GTP on IF2 interactions with fMet-tRNA(fMet) demonstrating that IF2 binds to initiator tRNA with submicromolar K-d and that affinity is altered by the G nucleotides only slightly. This-in conjunction with earlier reports on IF2 interactions with fMet-tRNA(fMet) in the context of the 30S initiation complex, where ppGpp was suggested to strongly inhibit fMet-tRNA(fMet) binding and GTP was suggested to strongly promote fMet-tRNA(fMet) binding-sheds new light on the mechanisms of the G-nucleotide-regulated fMet-tRNA(fMet) selection.</p>
  • Westgård, Theresa, et al. (författare)
  • Comprehensive geriatric assessment pilot of a randomized control study in a Swedish acute hospital: a feasibility study.
  • 2018
  • Ingår i: Pilot and feasibility studies. - 2055-5784. ; 4
  • Tidskriftsartikel (refereegranskat)abstract
    • Background: Comprehensive geriatric assessment (CGA) represent an important component of geriatric acute hospital care for frail older people, secured by a multidisciplinary team who addresses the multiple needs of physical health, functional ability, psychological state, cognition and social status. The primary objective of the pilot study was to determine feasibility for recruitment and retention rates. Secondary objectives were to establish proof of principle that CGA has the potential to increase patient safety. Methods: The CGA pilot took place at a University hospital in Western Sweden, from March to November 2016, with data analyses in March 2017. Participants were frail people aged 75 and older, who required an acute admission to hospital. Participants were recruited and randomized in the emergency room. The intervention group received CGA, a person-centered multidisciplinary team addressing health, participation, and safety. The control group received usual care. The main objective measured the recruitment procedure and retention rates. Secondary objectives were also collected regarding services received on the ward including discharge plan, care plan meeting and hospital risk assessments including risk for falls, nutrition, decubitus ulcers, and activities of daily living status. Result: Participants were recruited from the emergency department, over 32 weeks. Thirty participants were approached and 100% (30/30) were included and randomized, and 100% (30/30) met the inclusion criteria. Sixteen participants were included in the intervention and 14 participants were included in the control. At baseline, 100% (16/16) intervention and 100% (14/14) control completed the data collection. A positive propensity towards the secondary objectives for the intervention was also evidenced, as this group received more care assessments. There was an average difference between the intervention and control in occupational therapy assessment - 0.80 [95% CI 1.06, - 0.57], occupational therapy assistive devices - 0.73 [95% CI 1.00, - 0.47], discharge planning -0.21 [95% CI 0.43, 0.00] and care planning meeting 0.36 [95% CI-1.70, -0.02]. Controlling for documented risk assessments, the intervention had for falls - 0.94 [95% CI 1.08, - 0.08], nutrition - 0.87 [95% CI 1.06, - 0.67], decubitus ulcers - 0.94 [95% CI 1.08, - 0.80], and ADL status - 0.80 [95% CI 1.04, - 0.57]. Conclusion: The CGA pilot was feasible and proof that the intervention increased safety justifies carrying forward to a large-scale study.
  • Winkler, A., et al. (författare)
  • Magnetism in Re-based ferrimagnetic double perovskites
  • 2009
  • Ingår i: New Journal of Physics. - 1367-2630 .- 1367-2630. ; 11, s. 073047
  • Tidskriftsartikel (refereegranskat)abstract
    • <p>We have investigated spin and orbital magnetic moments of the Re 5d ion in the double perovskites A(2)FeReO(6) (A = Ba, Sr, Ca) by x-ray magnetic circular dichroism (XMCD) at the Re L(2,3) edges. In these ferrimagnetic compounds, an unusually large negative spin and positive orbital magnetic moment at the Re atoms was detected. The presence of a finite spin magnetic moment in a 'non-magnetic' double perovskite as observed in the double perovskite Sr(2)ScReO(6) proves that Re has also a small, but finite intrinsic magnetic moment. We further show for the examples of Ba and Ca that the usually neglected alkaline earth ions undoubtedly also contribute to the magnetism in the ferrimagnetic double perovskites.</p>
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