| 1. |
- Johansson, Linda C, 1983, et al.
(author)
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Structure of a photosynthetic reaction centre determined by serial femtosecond crystallography.
- 2013
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In: Nature communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 4
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Journal article (peer-reviewed)abstract
- Serial femtosecond crystallography is an X-ray free-electron-laser-based method with considerable potential to have an impact on challenging problems in structural biology. Here we present X-ray diffraction data recorded from microcrystals of the Blastochloris viridis photosynthetic reaction centre to 2.8Å resolution and determine its serial femtosecond crystallography structure to 3.5Å resolution. Although every microcrystal is exposed to a dose of 33MGy, no signs of X-ray-induced radiation damage are visible in this integral membrane protein structure.
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| 2. |
- Alonso-Mori, Roberto, et al.
(author)
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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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In: 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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Journal article (peer-reviewed)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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| 3. |
- Arnlund, David, et al.
(author)
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Visualizing a protein quake with time-resolved X-ray scattering at a free-electron laser
- 2014
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In: Nature Methods. - : Springer Science and Business Media LLC. - 1548-7091 .- 1548-7105. ; 11:9, s. 923-926
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Journal article (peer-reviewed)abstract
- We describe a method to measure ultrafast protein structural changes using time-resolved wide-angle X-ray scattering at an X-ray free-electron laser. We demonstrated this approach using multiphoton excitation of the Blastochloris viridis photosynthetic reaction center, observing an ultrafast global conformational change that arises within picoseconds and precedes the propagation of heat through the protein. This provides direct structural evidence for a 'protein quake': the hypothesis that proteins rapidly dissipate energy through quake-like structural motions.
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| 4. |
- Barty, A., et al.
(author)
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Self-terminating diffraction gates femtosecond X-ray nanocrystallography measurements
- 2012
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In: Nature Photonics. - 1749-4885 .- 1749-4893. ; 6:1, s. 35-40
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Journal article (peer-reviewed)abstract
- X-ray free-electron lasers have enabled new approaches to the structural determination of protein crystals that are too small or radiation-sensitive for conventional analysis1. For sufficiently short pulses, diffraction is collected before significant changes occur to the sample, and it has been predicted that pulses as short as 10 fs may be required to acquire atomic-resolution structural information1, 2, 3, 4. Here, we describe a mechanism unique to ultrafast, ultra-intense X-ray experiments that allows structural information to be collected from crystalline samples using high radiation doses without the requirement for the pulse to terminate before the onset of sample damage. Instead, the diffracted X-rays are gated by a rapid loss of crystalline periodicity, producing apparent pulse lengths significantly shorter than the duration of the incident pulse. The shortest apparent pulse lengths occur at the highest resolution, and our measurements indicate that current X-ray free-electron laser technology5 should enable structural determination from submicrometre protein crystals with atomic resolution.
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| 5. |
- Blösch, Günter, et al.
(author)
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Twenty-three unsolved problems in hydrology (UPH) - a community perspective
- 2019
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In: Hydrological Sciences Journal. - : Informa UK Limited. - 0262-6667 .- 2150-3435. ; 64:10, s. 1141-1158
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Journal article (peer-reviewed)abstract
- This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through online media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focused on the process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come.
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| 6. |
- Kern, Jan, et al.
(author)
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Room temperature femtosecond X-ray diffraction of photosystem II microcrystals
- 2012
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In: 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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Journal article (peer-reviewed)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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| 7. |
- Kern, Jan, et al.
(author)
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Simultaneous Femtosecond X-ray Spectroscopy and Diffraction of Photosystem II at Room Temperature
- 2013
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In: Science. - : American Association for the Advancement of Science (AAAS). - 0036-8075 .- 1095-9203. ; 340:6131, s. 491-495
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Journal article (peer-reviewed)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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| 8. |
- Sierra, Raymond G., et al.
(author)
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Nanoflow electrospinning serial femtosecond crystallography
- 2012
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In: Acta Crystallographica Section D. - : Wiley-Blackwell. - 0907-4449 .- 1399-0047. ; 68, s. 1584-1587
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Journal article (peer-reviewed)abstract
- An electrospun liquid microjet has been developed that delivers protein microcrystal suspensions at flow rates of 0.14-3.1 mu l min(-1) to perform serial femtosecond crystallography (SFX) studies with X-ray lasers. Thermolysin microcrystals flowed at 0.17 mu l min(-1) and diffracted to beyond 4 angstrom resolution, producing 14 000 indexable diffraction patterns, or four per second, from 140 mu g of protein. Nanoflow electrospinning extends SFX to biological samples that necessitate minimal sample consumption.
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| 9. |
- Addor, Nans, et al.
(author)
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Propagation of biases in climate models from the synoptic to the regional scale : Implications for bias adjustment
- 2016
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In: Journal of Geophysical Research - Atmospheres. - 2169-897X .- 2169-8996. ; 121:5, s. 2075-2089
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Journal article (peer-reviewed)abstract
- Bias adjustment methods usually do not account for the origins of biases in climate models and instead perform empirical adjustments. Biases in the synoptic circulation are for instance often overlooked when postprocessing regional climate model (RCM) simulations driven by general circulation models (GCMs). Yet considering atmospheric circulation helps to establish links between the synoptic and the regional scale, and thereby provides insights into the physical processes leading to RCM biases. Here we investigate how synoptic circulation biases impact regional climate simulations and influence our ability to mitigate biases in precipitation and temperature using quantile mapping. We considered 20 GCM-RCM combinations from the ENSEMBLES project and characterized the dominant atmospheric flow over the Alpine domain using circulation types. We report in particular a systematic overestimation of the frequency of westerly flow in winter. We show that it contributes to the generalized overestimation of winter precipitation over Switzerland, and this wet regional bias can be reduced by improving the simulation of synoptic circulation. We also demonstrate that statistical bias adjustment relying on quantile mapping is sensitive to circulation biases, which leads to residual errors in the postprocessed time series. Overall, decomposing GCM-RCM time series using circulation types reveals connections missed by analyses relying on monthly or seasonal values. Our results underscore the necessity to better diagnose process misrepresentation in climate models to progress with bias adjustment and impact modeling.
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| 10. |
- Addor, Nans, et al.
(author)
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Robust changes and sources of uncertainty in the projected hydrological regimes of Swiss catchments
- 2014
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In: Water resources research. - 0043-1397 .- 1944-7973. ; 50:10, s. 7541-7562
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Journal article (peer-reviewed)abstract
- Projections of discharge are key for future water resources management. These projections are subject to uncertainties, which are difficult to handle in the decision process on adaptation strategies. Uncertainties arise from different sources such as the emission scenarios, the climate models and their postprocessing, the hydrological models, and the natural variability. Here we present a detailed and quantitative uncertainty assessment, based on recent climate scenarios for Switzerland (CH2011 data set) and covering catchments representative for midlatitude alpine areas. This study relies on a particularly wide range of discharge projections resulting from the factorial combination of 3 emission scenarios, 10–20 regional climate models, 2 postprocessing methods, and 3 hydrological models of different complexity. This enabled us to decompose the uncertainty in the ensemble of projections using analyses of variance (ANOVA). We applied the same modeling setup to six catchments to assess the influence of catchment characteristics on the projected streamflow, and focused on changes in the annual discharge cycle. The uncertainties captured by our setup originate mainly from the climate models and natural climate variability, but the choice of emission scenario plays a large role by the end of the 21st century. The contribution of the hydrological models to the projection uncertainty varied strongly with catchment elevation. The discharge changes were compared to the estimated natural decadal variability, which revealed that a climate change signal emerges even under the lowest emission scenario (RCP2.6) by the end of the century. Limiting emissions to RCP2.6 levels would nevertheless reduce the largest regime changes by the end of the century by approximately a factor of two, in comparison to impacts projected for the high emission scenario SRES A2. We finally show that robust regime changes emerge despite the projection uncertainty. These changes are significant and are consistent across a wide range of scenarios and catchments. We propose their identification as a way to aid decision making under uncertainty.
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