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1.  Imaging live cell in micro-liquid enclosure by X-ray laser diffraction 
Nature Communications  2014;5:3052.
Emerging X-ray free-electron lasers with femtosecond pulse duration enable single-shot snapshot imaging almost free from sample damage by outrunning major radiation damage processes. In bioimaging, it is essential to keep the sample close to its natural state. Conventional high-resolution imaging, however, suffers from severe radiation damage that hinders live cell imaging. Here we present a method for capturing snapshots of live cells kept in a micro-liquid enclosure array by X-ray laser diffraction. We place living Microbacterium lacticum cells in an enclosure array and successively expose each enclosure to a single X-ray laser pulse from the SPring-8 Angstrom Compact Free-Electron Laser. The enclosure itself works as a guard slit and allows us to record a coherent diffraction pattern from a weakly-scattering submicrometre-sized cell with a clear fringe extending up to a 28-nm full-period resolution. The reconstructed image reveals living whole-cell structures without any staining, which helps advance understanding of intracellular phenomena.
Live cell imaging at high resolution is very challenging because cells die upon prolonged radiation exposure. Kimura et al. overcome this problem by using pulsed coherent X-ray diffraction to image live microbacterium in a nanofabricated liquid enclosure at resolution far exceeding optical methods.
doi:10.1038/ncomms4052
PMCID: PMC3896756  PMID: 24394916
2.  Femtosecond X-ray protein nanocrystallography 
Chapman, Henry N. | Fromme, Petra | Barty, Anton | White, Thomas A. | Kirian, Richard A. | Aquila, Andrew | Hunter, Mark S. | Schulz, Joachim | DePonte, Daniel P. | Weierstall, Uwe | Doak, R. Bruce | Maia, Filipe R. N. C. | Martin, Andrew V. | Schlichting, Ilme | Lomb, Lukas | Coppola, Nicola | Shoeman, Robert L. | Epp, Sascha W. | Hartmann, Robert | Rolles, Daniel | Rudenko, Artem | Foucar, Lutz | Kimmel, Nils | Weidenspointner, Georg | Holl, Peter | Liang, Mengning | Barthelmess, Miriam | Caleman, Carl | Boutet, Sébastien | Bogan, Michael J. | Krzywinski, Jacek | Bostedt, Christoph | Bajt, Saša | Gumprecht, Lars | Rudek, Benedikt | Erk, Benjamin | Schmidt, Carlo | Hömke, André | Reich, Christian | Pietschner, Daniel | Strüder, Lothar | Hauser, Günter | Gorke, Hubert | Ullrich, Joachim | Herrmann, Sven | Schaller, Gerhard | Schopper, Florian | Soltau, Heike | Kühnel, Kai-Uwe | Messerschmidt, Marc | Bozek, John D. | Hau-Riege, Stefan P. | Frank, Matthias | Hampton, Christina Y. | Sierra, Raymond G. | Starodub, Dmitri | Williams, Garth J. | Hajdu, Janos | Timneanu, Nicusor | Seibert, M. Marvin | Andreasson, Jakob | Rocker, Andrea | Jönsson, Olof | Svenda, Martin | Stern, Stephan | Nass, Karol | Andritschke, Robert | Schröter, Claus-Dieter | Krasniqi, Faton | Bott, Mario | Schmidt, Kevin E. | Wang, Xiaoyu | Grotjohann, Ingo | Holton, James M. | Barends, Thomas R. M. | Neutze, Richard | Marchesini, Stefano | Fromme, Raimund | Schorb, Sebastian | Rupp, Daniela | Adolph, Marcus | Gorkhover, Tais | Andersson, Inger | Hirsemann, Helmut | Potdevin, Guillaume | Graafsma, Heinz | Nilsson, Björn | Spence, John C. H.
Nature  2011;470(7332):73-77.
X-ray crystallography provides the vast majority of macromolecular structures, but the success of the method relies on growing crystals of sufficient size. In conventional measurements, the necessary increase in X-ray dose to record data from crystals that are too small leads to extensive damage before a diffraction signal can be recorded1-3. It is particularly challenging to obtain large, well-diffracting crystals of membrane proteins, for which fewer than 300 unique structures have been determined despite their importance in all living cells. Here we present a method for structure determination where single-crystal X-ray diffraction ‘snapshots’ are collected from a fully hydrated stream of nanocrystals using femtosecond pulses from a hard-X-ray free-electron laser, the Linac Coherent Light Source4. We prove this concept with nanocrystals of photosystem I, one of the largest membrane protein complexes5. More than 3,000,000 diffraction patterns were collected in this study, and a three-dimensional data set was assembled from individual photosystem I nanocrystals (~200 nm to 2 μm in size). We mitigate the problem of radiation damage in crystallography by using pulses briefer than the timescale of most damage processes6. This offers a new approach to structure determination of macromolecules that do not yield crystals of sufficient size for studies using conventional radiation sources or are particularly sensitive to radiation damage.
doi:10.1038/nature09750
PMCID: PMC3429598  PMID: 21293373
3.  Femtosecond nanocrystallography using X-Ray Lasers for membrane protein structure determination 
The invention of Free Electron X-ray Lasers has opened a new era for membrane protein structure determination with the recent first proof-of-principle of the new concept of femtosecond nanocrystallography. Structure determination is based on thousands of diffraction snapshots that are collected on a fully hydrated stream of nanocrystals. This review provides a summary of the method and describes how femtosecond X-ray crystallography overcomes the radiation damage problem in X-ray crystallography, avoids the need for growth and freezing of large single crystals while offering a new method for direct digital phase determination by making use of the fully coherent nature of the X-ray beam. We briefly review the possibilities for time-resolved crystallography, and the potential for making “molecular movies” of membrane proteins at work.
doi:10.1016/j.sbi.2011.06.001
PMCID: PMC3413407  PMID: 21752635
4.  Solving structure with sparse, randomly-oriented x-ray data 
Optics Express  2012;20(12):13129-13137.
Single-particle imaging experiments of biomolecules at x-ray free-electron lasers (XFELs) require processing hundreds of thousands of images that contain very few x-rays. Each low-fluence image of the diffraction pattern is produced by a single, randomly oriented particle, such as a protein. We demonstrate the feasibility of recovering structural information at these extremes using low-fluence images of a randomly oriented 2D x-ray mask. Successful reconstruction is obtained with images averaging only 2.5 photons per frame, where it seems doubtful there could be information about the state of rotation, let alone the image contrast. This is accomplished with an expectation maximization algorithm that processes the low-fluence data in aggregate, and without any prior knowledge of the object or its orientation. The versatility of the method promises, more generally, to redefine what measurement scenarios can provide useful signal.
doi:10.1364/OE.20.013129
PMCID: PMC3635695  PMID: 22714341
(040.7480) X-rays, soft x-rays, extreme ultraviolet (EUV); (110.7440) X-ray imaging; (000.2190) Experimental physics; (110.3055) Information theoretical analysis; (110.4155) Multiframe image processing; (040.0040) Detectors
5.  High-speed classification of coherent X-ray diffraction patterns on the K computer for high-resolution single biomolecule imaging 
Journal of Synchrotron Radiation  2013;20(Pt 6):899-904.
A code with an algorithm for high-speed classification of X-ray diffraction patterns has been developed. Results obtained for a set of 1 × 106 simulated diffraction patterns are also reported.
Single-particle coherent X-ray diffraction imaging using an X-ray free-electron laser has the potential to reveal the three-dimensional structure of a biological supra-molecule at sub-nanometer resolution. In order to realise this method, it is necessary to analyze as many as 1 × 106 noisy X-ray diffraction patterns, each for an unknown random target orientation. To cope with the severe quantum noise, patterns need to be classified according to their similarities and average similar patterns to improve the signal-to-noise ratio. A high-speed scalable scheme has been developed to carry out classification on the K computer, a 10PFLOPS supercomputer at RIKEN Advanced Institute for Computational Science. It is designed to work on the real-time basis with the experimental diffraction pattern collection at the X-ray free-electron laser facility SACLA so that the result of classification can be feedback for optimizing experimental parameters during the experiment. The present status of our effort developing the system and also a result of application to a set of simulated diffraction patterns is reported. About 1 × 106 diffraction patterns were successfully classificatied by running 255 separate 1 h jobs in 385-node mode.
doi:10.1107/S0909049513022152
PMCID: PMC3795552  PMID: 24121336
X-ray free-electron laser; K computer; single-particle coherent diffraction imaging; classification of diffraction patterns; big-data analysis
6.  Time-resolved protein nanocrystallography using an X-ray free-electron laser 
Aquila, Andrew | Hunter, Mark S | Bruce Doak, R. | Kirian, Richard A. | Fromme, Petra | White, Thomas A. | Andreasson, Jakob | Arnlund, David | Bajt, Saša | Barends, Thomas R. M. | Barthelmess, Miriam | Bogan, Michael J. | Bostedt, Christoph | Bottin, Hervé | Bozek, John D. | Caleman, Carl | Coppola, Nicola | Davidsson, Jan | DePonte, Daniel P. | Elser, Veit | Epp, Sascha W. | Erk, Benjamin | Fleckenstein, Holger | Foucar, Lutz | Frank, Matthias | Fromme, Raimund | Graafsma, Heinz | Grotjohann, Ingo | Gumprecht, Lars | Hajdu, Janos | Hampton, Christina Y. | Hartmann, Andreas | Hartmann, Robert | Hau-Riege, Stefan | Hauser, Günter | Hirsemann, Helmut | Holl, Peter | Holton, James M. | Hömke, André | Johansson, Linda | Kimmel, Nils | Kassemeyer, Stephan | Krasniqi, Faton | Kühnel, Kai-Uwe | Liang, Mengning | Lomb, Lukas | Malmerberg, Erik | Marchesini, Stefano | Martin, Andrew V. | Maia, Filipe R.N.C. | Messerschmidt, Marc | Nass, Karol | Reich, Christian | Neutze, Richard | Rolles, Daniel | Rudek, Benedikt | Rudenko, Artem | Schlichting, Ilme | Schmidt, Carlo | Schmidt, Kevin E. | Schulz, Joachim | Seibert, M. Marvin | Shoeman, Robert L. | Sierra, Raymond | Soltau, Heike | Starodub, Dmitri | Stellato, Francesco | Stern, Stephan | Strüder, Lothar | Timneanu, Nicusor | Ullrich, Joachim | Wang, Xiaoyu | Williams, Garth J. | Weidenspointner, Georg | Weierstall, Uwe | Wunderer, Cornelia | Barty, Anton | Spence, John C. H | Chapman, Henry N.
Optics express  2012;20(3):2706-2716.
We demonstrate the use of an X-ray free electron laser synchronized with an optical pump laser to obtain X-ray diffraction snapshots from the photoactivated states of large membrane protein complexes in the form of nanocrystals flowing in a liquid jet. Light-induced changes of Photosystem I-Ferredoxin co-crystals were observed at time delays of 5 to 10 μs after excitation. The result correlates with the microsecond kinetics of electron transfer from Photosystem I to ferredoxin. The undocking process that follows the electron transfer leads to large rearrangements in the crystals that will terminally lead to the disintegration of the crystals. We describe the experimental setup and obtain the first time-resolved femtosecond serial X-ray crystallography results from an irreversible photo-chemical reaction at the Linac Coherent Light Source. This technique opens the door to time-resolved structural studies of reaction dynamics in biological systems.
PMCID: PMC3413412  PMID: 22330507
7.  Time-resolved protein nanocrystallography using an X-ray free-electron laser 
Aquila, Andrew | Hunter, Mark S. | Doak, R. Bruce | Kirian, Richard A. | Fromme, Petra | White, Thomas A. | Andreasson, Jakob | Arnlund, David | Bajt, Saša | Barends, Thomas R. M. | Barthelmess, Miriam | Bogan, Michael J. | Bostedt, Christoph | Bottin, Hervé | Bozek, John D. | Caleman, Carl | Coppola, Nicola | Davidsson, Jan | DePonte, Daniel P. | Elser, Veit | Epp, Sascha W. | Erk, Benjamin | Fleckenstein, Holger | Foucar, Lutz | Frank, Matthias | Fromme, Raimund | Graafsma, Heinz | Grotjohann, Ingo | Gumprecht, Lars | Hajdu, Janos | Hampton, Christina Y. | Hartmann, Andreas | Hartmann, Robert | Hau-Riege, Stefan | Hauser, Günter | Hirsemann, Helmut | Holl, Peter | Holton, James M. | Hömke, André | Johansson, Linda | Kimmel, Nils | Kassemeyer, Stephan | Krasniqi, Faton | Kühnel, Kai-Uwe | Liang, Mengning | Lomb, Lukas | Malmerberg, Erik | Marchesini, Stefano | Martin, Andrew V. | Maia, Filipe R.N.C. | Messerschmidt, Marc | Nass, Karol | Reich, Christian | Neutze, Richard | Rolles, Daniel | Rudek, Benedikt | Rudenko, Artem | Schlichting, Ilme | Schmidt, Carlo | Schmidt, Kevin E. | Schulz, Joachim | Seibert, M. Marvin | Shoeman, Robert L. | Sierra, Raymond | Soltau, Heike | Starodub, Dmitri | Stellato, Francesco | Stern, Stephan | Strüder, Lothar | Timneanu, Nicusor | Ullrich, Joachim | Wang, Xiaoyu | Williams, Garth J. | Weidenspointner, Georg | Weierstall, Uwe | Wunderer, Cornelia | Barty, Anton | Spence, John C. H. | Chapman, Henry N.
Optics Express  2012;20(3):2706-2716.
We demonstrate the use of an X-ray free electron laser synchronized with an optical pump laser to obtain X-ray diffraction snapshots from the photoactivated states of large membrane protein complexes in the form of nanocrystals flowing in a liquid jet. Light-induced changes of Photosystem I-Ferredoxin co-crystals were observed at time delays of 5 to 10 µs after excitation. The result correlates with the microsecond kinetics of electron transfer from Photosystem I to ferredoxin. The undocking process that follows the electron transfer leads to large rearrangements in the crystals that will terminally lead to the disintegration of the crystals. We describe the experimental setup and obtain the first time-resolved femtosecond serial X-ray crystallography results from an irreversible photo-chemical reaction at the Linac Coherent Light Source. This technique opens the door to time-resolved structural studies of reaction dynamics in biological systems.
doi:10.1364/OE.20.002706
PMCID: PMC3413412  PMID: 22330507
(170.7160) Ultrafast technology; (170.7440) X-ray imaging; (140.3450) Laser-induced chemistry; (140.7090) Ultrafast lasers; (170.0170) Medical optics and biotechnology
8.  Serial femtosecond X-ray diffraction of 30S ribosomal subunit microcrystals in liquid suspension at ambient temperature using an X-ray free-electron laser 
Serial femtosecond X-ray (SFX) diffraction extending beyond 6 Å resolution using T. thermophilus 30S ribosomal subunit crystals is reported.
High-resolution ribosome structures determined by X-ray crystallography have provided important insights into the mechanism of translation. Such studies have thus far relied on large ribosome crystals kept at cryogenic temperatures to reduce radiation damage. Here, the application of serial femtosecond X-ray crystallography (SFX) using an X-ray free-electron laser (XFEL) to obtain diffraction data from ribosome microcrystals in liquid suspension at ambient temperature is described. 30S ribosomal subunit microcrystals diffracted to beyond 6 Å resolution, demonstrating the feasibility of using SFX for ribosome structural studies. The ability to collect diffraction data at near-physiological temperatures promises to provide fundamental insights into the structural dynamics of the ribosome and its functional complexes.
doi:10.1107/S174430911302099X
PMCID: PMC3758164  PMID: 23989164
30S ribosomal subunit; serial femtosecond X-ray crystallography; X-ray free-electron laser; ribosome
9.  Emerging opportunities in structural biology with X-ray free-electron lasers 
X-ray free-electron lasers (X-FELs) produce X-ray pulses with extremely brilliant peak intensity and ultrashort pulse duration. It has been proposed that radiation damage can be “outrun” by using an ultra intense and short X-FEL pulse that passes a biological sample before the onset of significant radiation damage. The concept of “diffraction-before-destruction” has been demonstrated recently at the Linac Coherent Light Source, the first operational hard X-ray FEL, for protein nanocrystals and giant virus particles. The continuous diffraction patterns from single particles allow solving the classical “phase problem” by the oversampling method with iterative algorithms. If enough data are collected from many identical copies of a (biological) particle, its three-dimensional structure can be reconstructed. We review the current status and future prospects of serial femtosecond crystallography (SFX) and single-particle coherent diffraction imaging (CDI) with X-FELs.
doi:10.1016/j.sbi.2012.07.015
PMCID: PMC3495068  PMID: 22922042
10.  Structure-factor analysis of femtosecond microdiffraction patterns from protein nanocrystals 
A complete set of structure factors has been extracted from hundreds of thousands of femtosecond X-ray diffraction patterns from randomly oriented Photosystem I membrane protein nanocrystals, using the Monte Carlo method of intensity integration. The data, collected at the Linac Coherent Light Source, are compared with conventional single-crystal data collected at a synchrotron source, and the quality of each data set was found to be similar.
A complete set of structure factors has been extracted from hundreds of thousands of femtosecond single-shot X-ray microdiffraction patterns taken from randomly oriented nanocrystals. The method of Monte Carlo integration over crystallite size and orientation was applied to experimental data from Photosystem I nanocrystals. This arrives at structure factors from many partial reflections without prior knowledge of the particle-size distribution. The data were collected at the Linac Coherent Light Source (the first hard-X-ray laser user facility), to which was fitted a hydrated protein nanocrystal injector jet, according to the method of serial crystallography. The data are single ‘still’ diffraction snapshots, each from a different nanocrystal with sizes ranging between 100 nm and 2 µm, so the angular width of Bragg peaks was dominated by crystal-size effects. These results were compared with single-crystal data recorded from large crystals of Photosystem I at the Advanced Light Source and the quality of the data was found to be similar. The implications for improving the efficiency of data collection by allowing the use of very small crystals, for radiation-damage reduction and for time-resolved diffraction studies at room temperature are discussed.
doi:10.1107/S0108767310050981
PMCID: PMC3066792  PMID: 21325716
nanocrystals; femtosecond diffraction; free-electron lasers; Monte Carlo methods; protein microdiffraction
11.  Structure of a photosynthetic reaction centre determined by serial femtosecond crystallography 
Nature Communications  2013;4:2911.
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 2.8 Å resolution and determine its serial femtosecond crystallography structure to 3.5 Å resolution. Although every microcrystal is exposed to a dose of 33 MGy, no signs of X-ray-induced radiation damage are visible in this integral membrane protein structure.
Serial femtosecond crystallography is an X-ray free-electron-laser-based method that uses X-ray bursts to determine protein structures. Here the authors present the structure of a photosynthetic reaction centre, an integral membrane protein, achieved with no sign of X-ray-induced radiation damage.
doi:10.1038/ncomms3911
PMCID: PMC3905732  PMID: 24352554
12.  Selective imaging of nano-particle contrast agents by a single-shot x-ray diffraction technique 
Optics express  2010;18(12):13271-13278.
Iron oxide nano-particles have very different x-ray diffraction properties from tissue. They can be clearly visualized against suppressed tissue background in a single-shot x-ray diffraction imaging technique. This technique is able to acquire both diffraction and absorption images from a single grating-modulated projection image through analysis in the spatial frequency domain. We describe the use of two orthogonal transmission gratings to selectively retain diffraction signal from iron oxide particles that are larger than a threshold size, while eliminating the background signal from soft tissue and bone. This approach should help the tracking of functionalized particles in cell labeling and targeted therapy.
PMCID: PMC3100656  PMID: 20588456
13.  THE MICROCRYSTALLINE STRUCTURE OF CELLULOSE IN CELL WALLS OF COTTON, RAMIE, AND JUTE FIBERS AS REVEALED BY NEGATIVE STAINING OF SECTIONS 
The Journal of Cell Biology  1966;29(2):181-197.
With a new technique of negative staining of sections, it has been possible to observe directly, in ultrathin sections under the electron microscope, the original microcrystalline and microfibrillar structure of cellulose as it occurs in living cells. This method has advantages over the study of isolated fibers used so far by others, in that the original arrangement of microfibrils is better preserved, and their collapse into larger fibrillar units is prevented. With this method, the cell walls of ramie, jute, and cotton fibers have been studied. The size (diameter, 25 to 40 A) and the longitudinal periodicity observed in the single microfibrils and the orientation and spatial arrangement of the microcrystallite within the microfibrils are found to correspond with the latest models derived by others from data obtained by indirect methods such as X-ray diffraction. The microfibril size of about 35 A, found by measuring these structures in sections, agrees with the latest conclusions reached by others in recent work with isolated fibrils.
PMCID: PMC2106906  PMID: 4164010
14.  Self-terminating diffraction gates femtosecond X-ray nanocrystallography measurements 
Nature photonics  2011;6:35-40.
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 information1–4. 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.
doi:10.1038/nphoton.2011.297
PMCID: PMC3783007  PMID: 24078834
15.  RELION: Implementation of a Bayesian approach to cryo-EM structure determination 
Journal of Structural Biology  2012;180(3):519-530.
RELION, for REgularized LIkelihood OptimizatioN, is an open-source computer program for the refinement of macromolecular structures by single-particle analysis of electron cryo-microscopy (cryo-EM) data. Whereas alternative approaches often rely on user expertise for the tuning of parameters, RELION uses a Bayesian approach to infer parameters of a statistical model from the data. This paper describes developments that reduce the computational costs of the underlying maximum a posteriori (MAP) algorithm, as well as statistical considerations that yield new insights into the accuracy with which the relative orientations of individual particles may be determined. A so-called gold-standard Fourier shell correlation (FSC) procedure to prevent overfitting is also described. The resulting implementation yields high-quality reconstructions and reliable resolution estimates with minimal user intervention and at acceptable computational costs.
doi:10.1016/j.jsb.2012.09.006
PMCID: PMC3690530  PMID: 23000701
Electron microscopy; Single-particle analysis; Maximum likelihood; Image processing; Software development
16.  How single molecule detection measures the dynamic actions of life 
HFSP Journal  2007;1(1):15-29.
Biomolecules dynamically work in cells in which a variety of molecules assemble and interact in unique manner. The molecular mechanisms underlying several biological processes have been elucidated from the results obtained from the descriptions of cell function, from the snapshots of the structures of biomolecules involved in these processes, and from the biochemical properties of these reactions in vitro. Recently developed single molecule measurements have revealed the dynamic properties of the biomolecules that have been hidden in the data that have been averaged over large numbers of molecules in both ensemble measurement and in cells. Single molecule imaging and manipulation of single molecules have allowed the visualization of the dynamic operations of molecular motors, enzymatic reactions, structural dynamics of biomolecules, and cell signaling processes. The results have shown that the single molecule techniques are powerful tools to monitor the dynamic actions of biomolecules and their assemblies. This approach has been applied to a variety of fields within the life sciences. As new information emerges about the dynamic actions of biomolecules using methods of single molecule detection new views on how biological processes work will be revealed.
doi:10.2976/1.2723643
PMCID: PMC2645551  PMID: 19404457
17.  Classifying and assembling two-dimensional X-ray laser diffraction patterns of a single particle to reconstruct the three-dimensional diffraction intensity function: resolution limit due to the quantum noise 
A new algorithm is developed for reconstructing the high-resolution three-dimensional diffraction intensity function of a globular biological macromolecule from many quantum-noise-limited two-dimensional X-ray laser diffraction patterns, each for an unknown orientation. The structural resolution is expressed as a function of the incident X-ray intensity and quantities characterizing the target molecule.
A new two-step algorithm is developed for reconstructing the three-dimensional diffraction intensity of a globular biological macromolecule from many experimentally measured quantum-noise-limited two-dimensional X-ray laser diffraction patterns, each for an unknown orientation. The first step is classification of the two-dimensional patterns into groups according to the similarity of direction of the incident X-rays with respect to the molecule and an averaging within each group to reduce the noise. The second step is detection of common intersecting circles between the signal-enhanced two-dimensional patterns to identify their mutual location in the three-dimensional wavenumber space. The newly developed algorithm enables one to detect a signal for classification in noisy experimental photon-count data with as low as ∼0.1 photons per effective pixel. The wavenumber of such a limiting pixel determines the attainable structural resolution. From this fact, the resolution limit due to the quantum noise attainable by this new method of analysis as well as two important experimental parameters, the number of two-dimensional patterns to be measured (the load for the detector) and the number of pairs of two-dimensional patterns to be analysed (the load for the computer), are derived as a function of the incident X-ray intensity and quantities characterizing the target molecule.
doi:10.1107/S010876731200493X
PMCID: PMC3329770  PMID: 22514069
biological macromolecules; classification of two-dimensional diffraction patterns; common intersecting circles; attainable structural resolution
18.  SnapShot-Seq: A Method for Extracting Genome-Wide, In Vivo mRNA Dynamics from a Single Total RNA Sample 
PLoS ONE  2014;9(2):e89673.
mRNA synthesis, processing, and destruction involve a complex series of molecular steps that are incompletely understood. Because the RNA intermediates in each of these steps have finite lifetimes, extensive mechanistic and dynamical information is encoded in total cellular RNA. Here we report the development of SnapShot-Seq, a set of computational methods that allow the determination of in vivo rates of pre-mRNA synthesis, splicing, intron degradation, and mRNA decay from a single RNA-Seq snapshot of total cellular RNA. SnapShot-Seq can detect in vivo changes in the rates of specific steps of splicing, and it provides genome-wide estimates of pre-mRNA synthesis rates comparable to those obtained via labeling of newly synthesized RNA. We used SnapShot-Seq to investigate the origins of the intrinsic bimodality of metazoan gene expression levels, and our results suggest that this bimodality is partly due to spillover of transcriptional activation from highly expressed genes to their poorly expressed neighbors. SnapShot-Seq dramatically expands the information obtainable from a standard RNA-Seq experiment.
doi:10.1371/journal.pone.0089673
PMCID: PMC3935918  PMID: 24586954
19.  A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS 
Journal of Applied Crystallography  2013;46(Pt 4):874-881.
Three-dimensional reciprocal space mapping by X-ray and electron diffraction [namely grazing-incidence X-ray diffraction (GIXD), reflection high-energy electron diffraction (RHEED) and grazing-incidence small-angle X-ray scattering (GISAXS)] was used to explore the internal structure and shape of differently oriented epitaxial Co/CaF2 facetted nanoparticles.
In this work epitaxial growth of cobalt on CaF2(111), (110) and (001) surfaces has been extensively studied. It has been shown by atomic force microscopy that at selected growth conditions stand-alone faceted Co nanoparticles are formed on a fluorite surface. Grazing-incidence X-ray diffraction (GIXD) and reflection high-energy electron diffraction (RHEED) studies have revealed that the particles crystallize in the face-centered cubic lattice structure otherwise non-achievable in bulk cobalt under normal conditions. The particles were found to inherit lattice orientation from the underlying CaF2 layer. Three-dimensional reciprocal space mapping carried out using X-ray and electron diffraction has revealed that there exist long bright 〈111〉 streaks passing through the cobalt Bragg reflections. These streaks are attributed to stacking faults formed in the crystal lattice of larger islands upon coalescence of independently nucleated smaller islands. Distinguished from the stacking fault streaks, crystal truncation rods perpendicular to the {111} and {001} particle facets have been observed. Finally, grazing-incidence small-angle X-ray scattering (GISAXS) has been applied to decouple the shape-related scattering from that induced by the crystal lattice defects. Particle faceting has been verified by modeling the GISAXS patterns. The work demonstrates the importance of three-dimensional reciprocal space mapping in the study of epitaxial nanoparticles.
doi:10.1107/S0021889813008777
PMCID: PMC3769055  PMID: 24046491
cobalt-on-fluorite nanoparticles; grazing-incidence X-ray diffraction (GIXD); reflection high-energy electron diffraction (RHEED); grazing-incidence small-angle X-ray scattering (GISAXS); epitaxial growth; three-dimensional reciprocal space mapping
20.  The Ribosome Comes Alive 
Israel journal of chemistry  2010;50(1):95-98.
This essay is a reflection on the ways the X-ray structures of the ribosome are helping in the interpretation of cryogenic electron microscopy (cryo-EM) density maps showing the translating ribosome in motion. Through advances in classification methods, cryo-EM and single-particle reconstruction methods have recently evolved to the point where they can yield an array of structures from a single sample (“story in a sample”), providing snapshots of an entire subprocess of translation, such as translocation or decoding.
doi:10.1002/ijch.201000010
PMCID: PMC2976627  PMID: 21072331
protein synthesis; cryo-electron microscopy; molecular machines; dynamics
21.  Disentangling multidimensional femtosecond spectra of excitons by pulse shaping with coherent control 
The Journal of chemical physics  2004;120(18):8373-8378.
Sequences of carefully timed and shaped optical pulses provide femtosecond snapshots of molecular structure as well as electronic and vibrational dynamical processes, in analogy with multidimensional NMR. We apply a genetic learning algorithm towards the design of pulse sequences which simplify the multidimensional signals by controlling the relative intensities of various peaks. Numerical simulations demonstrate how poorly resolved weak features may be amplified and observed by using optimized optical pulses, specifically shaped to achieve a desired spectroscopic target.
doi:10.1063/1.1691020
PMCID: PMC2894816  PMID: 15267760
22.  Ultrafast spin-state photoswitching in a crystal and slower consecutive processes investigated by femtosecond optical spectroscopy and picosecond X-ray diffraction 
We report the spin state photo-switching dynamics in two polymorphs of a spin-crossover molecular complex triggered by a femtosecond laser flash, as determined by combining femtosecond optical pump-probe spectroscopy and picosecond X-ray diffraction techniques,. The light-driven transformations in the two polymorphs are compared. Combining both techniques and tracking how the X-ray data correlate with optical signals allows understanding of how electronic and structural degrees of freedom couple and play their role when the switchable molecules interact in the active crystalline medium. The study sheds light on crossing the border between femtochemistry at the molecular scale and femtoswitching at the material scale
doi:10.1039/c2cp23587k
PMCID: PMC3463002  PMID: 22294040
23.  Curariform Antagonists Bind in Different Orientations to Acetylcholine-binding Protein* 
The Journal of biological chemistry  2003;278(25):23020-23026.
Acetylcholine-binding protein (AChBP) recently emerged as a prototype for relating structure to function of the ligand binding domain of nicotinic acetylcholine receptors (AChRs). To understand interactions of competitive antagonists at the atomic structural level, we studied binding of the curare derivatives d-tubocurarine (d-TC) and metocurine to AChBP using computational methods, mutagenesis, and ligand binding measurements. To account for protein flexibility, we used a 2-ns molecular dynamics simulation of AChBP to generate multiple snapshots of the equilibrated dynamic structure to which optimal docking orientations were determined. Our results predict a predominant docking orientation for both d-TC and metocurine, but unexpectedly, the bound orientations differ fundamentally for each ligand. At one subunit interface of AChBP, the side chain of Tyr-89 closely approaches a positively charged nitrogen in d-TC but is farther away from the equivalent nitrogen in metocurine, whereas, at the opposing interface, side chains of Trp-53 and Gln-55 closely approach the metocurine scaffold but not that of d-TC. The different orientations correspond to ~170° rotation and ~30° degree tilt of the curare scaffold within the binding pocket. Mutagenesis of binding site residues in AChBP, combined with measurements of ligand binding, confirms the different docking orientations. Thus structurally similar ligands can adopt distinct orientations at receptor binding sites, posing challenges for interpreting structure-activity relationships for many drugs.
doi:10.1074/jbc.M301151200
PMCID: PMC3191914  PMID: 12682067
24.  A clustering approach to multireference alignment of single-particle projections in electron microscopy 
Journal of structural biology  2010;171(2):197-206.
Two-dimensional analysis of projections of single particles acquired by an electron microscope is a useful tool to help identifying the different kinds of projections present in a dataset and their different projection directions. Such analysis is also useful to distinguish between different kinds of particles or different particle conformations. In this paper we introduce a new algorithm for performing two-dimensional multireference alignment and classification that is based on a Hierarchical clustering approach using correntropy (instead of the more traditional correlation) and a modified criterion for the definition of the clusters specially suited for cases in which the Signal-to-Noise Ratio of the differences between classes is low. We show that our algorithm offers an improved sensitivity over current methods in use for distinguishing between different projection orientations and different particle conformations. This algorithm is publicly available through the software package Xmipp.
doi:10.1016/j.jsb.2010.03.011
PMCID: PMC2893300  PMID: 20362059
Single-particle analysis; 2D analysis; Multireference analysis; Electron microscopy
25.  Radiation damage in protein serial femtosecond crystallography using an x-ray free-electron laser 
X-ray free-electron lasers deliver intense femtosecond pulses that promise to yield high resolution diffraction data of nanocrystals before the destruction of the sample by radiation damage. Diffraction intensities of lysozyme nanocrystals collected at the Linac Coherent Light Source using 2 keV photons were used for structure determination by molecular replacement and analyzed for radiation damage as a function of pulse length and fluence. Signatures of radiation damage are observed for pulses as short as 70 fs. Parametric scaling used in conventional crystallography does not account for the observed effects.
doi:10.1103/PhysRevB.84.214111
PMCID: PMC3786679  PMID: 24089594

Results 1-25 (819804)