| 1. |
- Hattne, Johan, et al.
(författare)
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Accurate macromolecular structures using minimal measurements from X-ray free-electron lasers
- 2014
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Ingår i: Nature Methods. - 1548-7091 .- 1548-7105. ; 11:5, s. 545-548
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Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron laser (XFEL) sources enable the use of crystallography to solve three-dimensional macromolecular structures under native conditions and without radiation damage. Results to date, however, have been limited by the challenge of deriving accurate Bragg intensities from a heterogeneous population of microcrystals, while at the same time modeling the X-ray spectrum and detector geometry. Here we present a computational approach designed to extract meaningful high-resolution signals from fewer diffraction measurements.
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| 2. |
- Hattne, Johan, et al.
(författare)
-
Accurate macromolecular structures using minimal measurements from X-ray free-electron lasers
- 2014
-
Ingår i: Nature Methods. - : Springer Science and Business Media LLC. - 1548-7091 .- 1548-7105. ; 11:5, s. 545-548
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Tidskriftsartikel (refereegranskat)abstract
- X-ray free-electron laser (XFEL) sources enable the use of crystallography to solve three-dimensional macromolecular structures under native conditions and without radiation damage. Results to date, however, have been limited by the challenge of deriving accurate Bragg intensities from a heterogeneous population of microcrystals, while at the same time modeling the X-ray spectrum and detector geometry. Here we present a computational approach designed to extract meaningful high-resolution signals from fewer diffraction measurements.
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| 3. |
- Kern, Jan, et al.
(författare)
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Simultaneous Femtosecond X-ray Spectroscopy and Diffraction of Photosystem II at Room Temperature
- 2013
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Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 340:6131, s. 491-495
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Tidskriftsartikel (refereegranskat)abstract
- Intense femtosecond x-ray pulses produced at the Linac Coherent Light Source (LCLS) were used for simultaneous x-ray diffraction (XRD) and x-ray emission spectroscopy (XES) of microcrystals of photosystem II (PS II) at room temperature. This method probes the overall protein structure and the electronic structure of the Mn4CaO5 cluster in the oxygen-evolving complex of PS II. XRD data are presented from both the dark state (S-1) and the first illuminated state (S-2) of PS II. Our simultaneous XRD-XES study shows that the PS II crystals are intact during our measurements at the LCLS, not only with respect to the structure of PS II, but also with regard to the electronic structure of the highly radiation-sensitive Mn4CaO5 cluster, opening new directions for future dynamics studies.
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| 4. |
- Kern, Jan, et al.
(författare)
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Taking snapshots of photosynthetic water oxidation using femtosecond X-ray diffraction and spectroscopy
- 2014
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 5, s. 4371-
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Tidskriftsartikel (refereegranskat)abstract
- The dioxygen we breathe is formed by light-induced oxidation of water in photosystem II. O-2 formation takes place at a catalytic manganese cluster within milliseconds after the photosystem II reaction centre is excited by three single-turnover flashes. Here we present combined X-ray emission spectra and diffraction data of 2-flash (2F) and 3-flash (3F) photosystem II samples, and of a transient 3F' state (250 mu s after the third flash), collected under functional conditions using an X-ray free electron laser. The spectra show that the initial O-O bond formation, coupled to Mn reduction, does not yet occur within 250 mu s after the third flash. Diffraction data of all states studied exhibit an anomalous scattering signal from Mn but show no significant structural changes at the present resolution of 4.5 angstrom. This study represents the initial frames in a molecular movie of the structural changes during the catalytic reaction in photosystem II.
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| 5. |
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| 6. |
- Alonso-Mori, Roberto, et al.
(författare)
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Energy-dispersive X-ray emission spectroscopy using an X-ray free-electron laser in a shot-by-shot mode
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:47, s. 19103-19107
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Tidskriftsartikel (refereegranskat)abstract
- The ultrabright femtosecond X-ray pulses provided by X-ray free-electron lasers open capabilities for studying the structure and dynamics of a wide variety of systems beyond what is possible with synchrotron sources. Recently, this probe-before-destroy approach has been demonstrated for atomic structure determination by serial X-ray diffraction of microcrystals. There has been the question whether a similar approach can be extended to probe the local electronic structure by X-ray spectroscopy. To address this, we have carried out femtosecond X-ray emission spectroscopy (XES) at the Linac Coherent Light Source using redox-active Mn complexes. XES probes the charge and spin states as well as the ligand environment, critical for understanding the functional role of redox-active metal sites. K beta(1,3) XES spectra of Mn-II and Mn-2(III,IV) complexes at room temperature were collected using a wavelength dispersive spectrometer and femtosecond X-ray pulses with an individual dose of up to > 100 MGy. The spectra were found in agreement with undamaged spectra collected at low dose using synchrotron radiation. Our results demonstrate that the intact electronic structure of redox active transition metal compounds in different oxidation states can be characterized with this shot-by-shot method. This opens the door for studying the chemical dynamics of metal catalytic sites by following reactions under functional conditions. The technique can be combined with X-ray diffraction to simultaneously obtain the geometric structure of the overall protein and the local chemistry of active metal sites and is expected to prove valuable for understanding the mechanism of important metalloproteins, such as photosystem II.
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| 7. |
- Kern, Jan, et al.
(författare)
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Room temperature femtosecond X-ray diffraction of photosystem II microcrystals
- 2012
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 109:25, s. 9721-9726
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Tidskriftsartikel (refereegranskat)abstract
- Most of the dioxygen on earth is generated by the oxidation of water by photosystem II (PS II) using light from the sun. This lightdriven, four-photon reaction is catalyzed by the Mn4CaO5 cluster located at the lumenal side of PS II. Various X-ray studies have been carried out at cryogenic temperatures to understand the intermediate steps involved in the water oxidation mechanism. However, the necessity for collecting data at room temperature, especially for studying the transient steps during the O-O bond formation, requires the development of new methodologies. In this paper we report room temperature X-ray diffraction data of PS II microcrystals obtained using ultrashort (<50 fs) 9 keV X-ray pulses from a hard X-ray free electron laser, namely the Linac Coherent Light Source. The results presented here demonstrate that the probe before destroy approach using an X-ray free electron laser works even for the highly-sensitive Mn4CaO5 cluster in PS II at room temperature. We show that these data are comparable to those obtained in synchrotron radiation studies as seen by the similarities in the overall structure of the helices, the protein subunits and the location of the various cofactors. This work is, therefore, an important step toward future studies for resolving the structure of the Mn4CaO5 cluster without any damage at room temperature, and of the reaction intermediates of PS II during O-O bond formation.
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| 8. |
- Milner-Gulland, E. J., et al.
(författare)
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Accounting for the Impact of Conservation on Human Well-Being
- 2014
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Ingår i: Conservation Biology. - : Wiley. - 0888-8892 .- 1523-1739. ; 28:5, s. 1160-1166
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Tidskriftsartikel (refereegranskat)abstract
- Conservationists are increasingly engaging with the concept of human well-being to improve the design and evaluation of their interventions. Since the convening of the influential Sarkozy Commission in 2009, development researchers have been refining conceptualizations and frameworks to understand and measure human well-being and are starting to converge on a common understanding of how best to do this. In conservation, the term human well-being is in widespread use, but there is a need for guidance on operationalizing it to measure the impacts of conservation interventions on people. We present a framework for understanding human well-being, which could be particularly useful in conservation. The framework includes 3 conditions; meeting needs, pursuing goals, and experiencing a satisfactory quality of life. We outline some of the complexities involved in evaluating the well-being effects of conservation interventions, with the understanding that well-being varies between people and over time and with the priorities of the evaluator. Key challenges for research into the well-being impacts of conservation interventions include the need to build up a collection of case studies so as to draw out generalizable lessons; harness the potential of modern technology to support well-being research; and contextualize evaluations of conservation impacts on well-being spatially and temporally within the wider landscape of social change. Pathways through the smog of confusion around the term well-being exist, and existing frameworks such as the Well-being in Developing Countries approach can help conservationists negotiate the challenges of operationalizing the concept. Conservationists have the opportunity to benefit from the recent flurry of research in the development field so as to carry out more nuanced and locally relevant evaluations of the effects of their interventions on human well-being. Consideracion del Impacto de la Conservacion sobre el Bienestar Humano
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| 9. |
- Rabalais, N. N., et al.
(författare)
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Eutrophication-driven deoxygenation in the coastal ocean
- 2014
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Ingår i: Oceanography. - : The Oceanography Society. - 1042-8275. ; 27:1, s. 172-183
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Tidskriftsartikel (refereegranskat)abstract
- Human activities, especially increased nutrient loads that set in motion a cascading chain of events related to eutrophication, accelerate development of hypoxia (lower oxygen concentration) in many areas of the world's coastal ocean. Climate changes and extreme weather events may modify hypoxia. Organismal and fisheries effects are at the heart of the coastal hypoxia issue, but more subtle regime shifts and trophic interactions are also cause for concern. The chemical milieu associated with declining dissolved oxygen concentrations affects the biogeochemical cycling of oxygen, carbon, nitrogen, phosphorus, silica, trace metals, and sulfide as observed in water column processes, shifts in sediment biogeochemistry, and increases in carbon, nitrogen, and sulfur, as well as shifts in their stable isotopes, in recently accumulated sediments. © 2014 by The Oceanography Society. All rights reserved.
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| 10. |
- Schock, Helena, 1984-, et al.
(författare)
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Anti-Mullerian hormone and risk of invasive serous ovarian cancer
- 2014
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Ingår i: Cancer Causes and Control. - : Springer. - 0957-5243 .- 1573-7225. ; 25:5, s. 583-589
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Tidskriftsartikel (refereegranskat)abstract
- Epithelial ovarian cancers either arise directly from Mullerian-type epithelium or acquire Mullerian characteristics in the course of neoplastic transformation. The anti-Mullerian hormone (AMH) causes regression of Mullerian structures during fetal development in males and has been shown to inhibit the growth of epithelial ovarian cancer. Therefore, we hypothesized that pre-diagnostic serum concentrations of AMH are inversely associated with risk of invasive serous ovarian cancer. A case-control study (107 cases, 208 controls) was nested within the population-based Finnish Maternity Cohort (1986-2007). The sample donated during the first trimester of the last pregnancy preceding cancer diagnosis of the case subjects was selected for the study. For each case, two controls, matched on age and date at sampling, as well as parity at sampling and at cancer diagnosis were selected. AMH was measured by a second-generation AMH ELISA. Conditional logistic regression was used to compute odds ratios (OR) and 95 % confidence intervals (CI) for invasive serous ovarian cancer associated with AMH concentrations. Overall AMH concentrations were not associated with risk of invasive serous ovarian cancer (OR 0.93; 95 % CI 0.49-1.77 for top vs. bottom tertile, P (trend) = 0.83). In women older than the median age at sampling (32.7 years), a doubling of AMH was associated with decreased risk (OR 0.69; 95 % CI 0.49-0.96), whereas an increased risk (OR 1.64; 95 % CI 1.06-2.54) was observed in younger women, P (homogeneity) = 0.002. In this first prospective investigation, risk of invasive serous ovarian cancer was not associated with pre-diagnostic AMH concentrations overall; however, the association may depend on age at AMH measurement.
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