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1.  Optimal fine ϕ-slicing for single-photon-counting pixel detectors 
Fine ϕ-slicing substantially improves scaling statistics and anomalous signal for diffraction data collection with hybrid pixel detectors.
The data-collection parameters used in a macromolecular diffraction experiment have a strong impact on data quality. A careful choice of parameters leads to better data and can make the difference between success and failure in phasing attempts, and will also result in a more accurate atomic model. The selection of parameters has to account for the application of the data in various phasing methods or high-resolution refinement. Furthermore, experimental factors such as crystal characteristics, available experiment time and the properties of the X-ray source and detector have to be considered. For many years, CCD detectors have been the prevalent type of detectors used in macromolecular crystallography. Recently, hybrid pixel X-ray detectors that operate in single-photon-counting mode have become available. These detectors have fundamentally different characteristics compared with CCD detectors and different data-collection strategies should be applied. Fine ϕ-slicing is a strategy that is particularly well suited to hybrid pixel detectors because of the fast readout time and the absence of readout noise. A large number of data sets were systematically collected from crystals of four different proteins in order to investigate the benefit of fine ϕ-­slicing on data quality with a noise-free detector. The results show that fine ϕ-slicing can substantially improve scaling statistics and anomalous signal provided that the rotation angle is comparable to half the crystal mosaicity.
PMCID: PMC3245722  PMID: 22194332
diffraction data collection; data-collection strategies; detectors; hybrid pixel detector; single-photon counting
2.  Automatic processing of macromolecular crystallography X-ray diffraction data at the ESRF 
Journal of Applied Crystallography  2013;46(Pt 3):804-810.
A system for the automatic reduction of single- and multi-position macromolecular crystallography data is presented.
The development of automated high-intensity macromolecular crystallography (MX) beamlines at synchrotron facilities has resulted in a remarkable increase in sample throughput. Developments in X-ray detector technology now mean that complete X-ray diffraction datasets can be collected in less than one minute. Such high-speed collection, and the volumes of data that it produces, often make it difficult for even the most experienced users to cope with the deluge. However, the careful reduction of data during experimental sessions is often necessary for the success of a particular project or as an aid in decision making for subsequent experiments. Automated data reduction pipelines provide a fast and reliable alternative to user-initiated processing at the beamline. In order to provide such a pipeline for the MX user community of the European Synchrotron Radiation Facility (ESRF), a system for the rapid automatic processing of MX diffraction data from single and multiple positions on a single or multiple crystals has been developed. Standard integration and data analysis programs have been incorporated into the ESRF data collection, storage and computing environment, with the final results stored and displayed in an intuitive manner in the ISPyB (information system for protein crystallography beamlines) database, from which they are also available for download. In some cases, experimental phase information can be automatically determined from the processed data. Here, the system is described in detail.
PMCID: PMC3654316  PMID: 23682196
automation; data processing; macromolecular crystallography; computer programs
3.  Identification of patterns in diffraction intensities affected by radiation exposure 
Journal of Synchrotron Radiation  2012;20(Pt 1):37-48.
Singular value decomposition of a matrix is a versatile tool used in multivariate data analysis. Here, its use is presented to test the validity of physical models applied when scaling diffraction data affected by radiation-induced changes.
In an X-ray diffraction experiment, the structure of molecules and the crystal lattice changes owing to chemical reactions and physical processes induced by the absorption of X-ray photons. These structural changes alter structure factors, affecting the scaling and merging of data collected at different absorbed doses. Many crystallographic procedures rely on the analysis of consistency between symmetry-equivalent reflections, so failure to account for the drift of their intensities hinders the structure solution and the interpretation of structural results. The building of a conceptual model of radiation-induced changes in macromolecular crystals is the first step in the process of correcting for radiation-induced inconsistencies in diffraction data. Here the complexity of radiation-induced changes in real and reciprocal space is analysed using matrix singular value decomposition applied to multiple complete datasets obtained from single crystals. The model consists of a resolution-dependent decay correction and a uniform-per-unique-reflection term modelling specific radiation-induced changes. This model is typically sufficient to explain radiation-induced effects observed in diffraction intensities. This analysis will guide the parameterization of the model, enabling its use in subsequent crystallographic calculations.
PMCID: PMC3526920  PMID: 23254654
radiation damage; matrix singular value decomposition; experimental phasing; radiolysis
4.  X-Ray Structure determination of the Glycine Cleavage System Protein H of Mycobacterium tuberculosis Using An Inverse Compton Synchrotron X-Ray Source 
Structural genomics discovery projects require ready access to both X-ray and NMR instrumentation which support the collection of experimental data needed to solve large numbers of novel protein structures. The most productive X-ray crystal structure determination laboratories make extensive frequent use of tunable synchrotron X-ray light to solve novel structures by anomalous diffraction methods. This requires that frozen cryo-protected crystals be shipped to large government-run synchrotron facilities for data collection. In an effort to eliminate the need to ship crystals for data collection, we have developed the first laboratory-scale synchrotron light source capable of performing many of the state-of-the-art synchrotron applications in X-ray science. This Compact Light Source is a first-in-class device that uses inverse Compton scattering to generate X-rays of sufficient flux, tunable wavelength and beam size to allow high-resolution X-ray diffraction data collection from protein crystals. We report on benchmarking tests of X-ray diffraction data collection with hen egg white lysozyme, and the successful high-resolution X-ray structure determination of the Glycine cleavage system protein H from Mycobacterium tuberculosis using diffraction data collected with the Compact Light Source X-ray beam.
PMCID: PMC2939714  PMID: 20364333
5.  How good can our beamlines be? 
A repetitive measurement of the same diffraction image allows to judge the performance of a data collection facility.
The accuracy of X-ray diffraction data depends on the properties of the crystalline sample and on the performance of the data-collection facility (synchrotron beamline elements, goniostat, detector etc.). However, it is difficult to evaluate the level of performance of the experimental setup from the quality of data sets collected in rotation mode, as various crystal properties such as mosaicity, non-uniformity and radiation damage affect the measured intensities. A multiple-image experiment, in which several analogous diffraction frames are recorded consecutively at the same crystal orientation, allows minimization of the influence of the sample properties. A series of 100 diffraction images of a thaumatin crystal were measured on the SBC beamline 19BM at the APS (Argonne National Laboratory). The obtained data were analyzed in the context of the performance of the data-collection facility. An objective way to estimate the uncertainties of individual reflections was achieved by analyzing the behavior of reflection intensities in the series of analogous diffraction images. The multiple-image experiment is found to be a simple and adequate method to decompose the random errors from the systematic errors in the data, which helps in judging the performance of a data-collection facility. In particular, displaying the intensity as a function of the frame number allows evaluation of the stability of the beam, the beamline elements and the detector with minimal influence of the crystal properties. Such an experiment permits evaluation of the highest possible data quality potentially achievable at the particular beamline.
PMCID: PMC3447404  PMID: 22993097
diffraction data precision; signal-to-noise ratio; measurement uncertainty; beamline performance
6.  Radiation damage in room-temperature data acquisition with the PILATUS 6M pixel detector 
Journal of Synchrotron Radiation  2011;18(Pt 3):318-328.
Observations of the dose-rate effect in continuous X-ray diffraction data acquisition at room temperature are presented.
The first study of room-temperature macromolecular crystallography data acquisition with a silicon pixel detector is presented, where the data are collected in continuous sample rotation mode, with millisecond read-out time and no read-out noise. Several successive datasets were collected sequentially from single test crystals of thaumatin and insulin. The dose rate ranged between ∼1320 Gy s−1 and ∼8420 Gy s−1 with corresponding frame rates between 1.565 Hz and 12.5 Hz. The data were analysed for global radiation damage. A previously unreported negative dose-rate effect is observed in the indicators of global radiation damage, which showed an approximately 75% decrease in D 1/2 at sixfold higher dose rate. The integrated intensity decreases in an exponential manner. Sample heating that could give rise to the enhanced radiation sensitivity at higher dose rate is investigated by collecting data between crystal temperatures of 298 K and 353 K. UV-Vis spectroscopy is used to demonstrate that disulfide radicals and trapped electrons do not accumulate at high dose rates in continuous data collection.
PMCID: PMC3133521  PMID: 21525639
room-temperature data collection; PILATUS 6M; dose rate; radiation damage
7.  Exploiting the anisotropy of anomalous scattering boosts the phasing power of SAD and MAD experiments 
It is shown that the anisotropy of anomalous scattering (AAS) is a significant and ubiquitous effect in data sets collected at an absorption edge and that its exploitation can substantially enhance the phasing power of single- or multi-wavelength anomalous diffraction. The improvements in the phases are typically of the same order of magnitude as those obtained in a conventional approach by adding a second-wavelength data set to a SAD experiment.
The X-ray polarization anisotropy of anomalous scattering in crystals of brominated nucleic acids and selenated proteins is shown to have significant effects on the diffraction data collected at an absorption edge. For conventionally collected single- or multi-wavelength anomalous diffraction data, the main manifestation of the anisotropy of anomalous scattering is the breakage of the equivalence between symmetry-related reflections, inducing intensity differences between them that can be exploited to yield extra phase information in the structure-solution process. A new formalism for describing the anisotropy of anomalous scattering which allows these effects to be incorporated into the general scheme of experimental phasing methods using an extended Harker construction is introduced. This requires a paradigm shift in the data-processing strategy, since the usual separation of the data-merging and phasing steps is abandoned. The data are kept unmerged down to the Harker construction, where the symmetry-breaking is explicitly modelled and refined and becomes a source of supplementary phase information. These ideas have been implemented in the phasing program SHARP. Refinements using actual data show that exploitation of the anisotropy of anomalous scattering can deliver substantial extra phasing power compared with conventional approaches using the same raw data. Examples are given that show improvements in the phases which are typically of the same order of magnitude as those obtained in a conventional approach by adding a second-wavelength data set to a SAD experiment. It is argued that such gains, which come essentially for free, i.e. without the collection of new data, are highly significant, since radiation damage can frequently preclude the collection of a second-wavelength data set. Finally, further developments in synchrotron instrumentation and in the design of data-collection strategies that could help to maximize these gains are outlined.
PMCID: PMC2467528  PMID: 18566507
anisotropy of anomalous scattering; phasing; SAD; MAD; polarized resonant diffraction
8.  The use of a mini-κ goniometer head in macromolecular crystallography diffraction experiments 
Hardware and software solutions for MX data-collection strategies using the EMBL/ESRF miniaturized multi-axis goniometer head are presented.
Most macromolecular crystallography (MX) diffraction experiments at synchrotrons use a single-axis goniometer. This markedly contrasts with small-molecule crystallography, in which the majority of the diffraction data are collected using multi-axis goniometers. A novel miniaturized κ-gonio­meter head, the MK3, has been developed to allow macromolecular crystals to be aligned. It is available on the majority of the structural biology beamlines at the ESRF, as well as elsewhere. In addition, the Strategy for the Alignment of Crystals (STAC) software package has been developed to facilitate the use of the MK3 and other similar devices. Use of the MK3 and STAC is streamlined by their incorporation into online analysis tools such as EDNA. The current use of STAC and MK3 on the MX beamlines at the ESRF is discussed. It is shown that the alignment of macromolecular crystals can result in improved diffraction data quality compared with data obtained from randomly aligned crystals.
PMCID: PMC3689527  PMID: 23793150
kappa goniometer; crystal alignment; data-collection strategies
9.  X-ray structure of perdeuterated diisopropyl fluorophosphatase (DFPase): perdeuteration of proteins for neutron diffraction 
The crystal structure of perdeuterated diisopropyl fluorophosphatase is reported and compared with the hydrogenated structure. Diffraction guidelines for neutron crystallography experiments are summarized.
The signal-to-noise ratio is one of the limiting factors in neutron macromolecular crystallography. Protein perdeuteration, which replaces all H atoms with deuterium, is a method of improving the signal-to-noise ratio of neutron crystallography experiments by reducing the incoherent scattering of the hydrogen isotope. Detailed analyses of perdeuterated and hydrogenated structures are necessary in order to evaluate the utility of perdeuterated crystals for neutron diffraction studies. The room-temperature X-ray structure of perdeuterated diisopropyl fluorophosphatase (DFPase) is reported at 2.1 Å resolution. Comparison with an independently refined hydrogenated room-temperature structure of DFPase revealed no major systematic differences, although the crystals of perdeuterated DFPase did not diffract neutrons. The lack of diffraction is examined with respect to data-collection and crystallo­graphic parameters. The diffraction characteristics of successful neutron structure determinations are presented as a guideline for future neutron diffraction studies of macromolecules. X-ray diffraction to beyond 2.0 Å resolution appears to be a strong predictor of successful neutron structures.
PMCID: PMC2852326  PMID: 20383004
diisopropyl fluorophosphatase; perdeuteration
10.  The kinetic dose limit in room-temperature time-resolved macromolecular crystallography 
Journal of Synchrotron Radiation  2012;19(Pt 2):264-273.
The effect of the X-ray dose on room-temperature time-resolved Laue data is discussed.
Protein X-ray structures are determined with ionizing radiation that damages the protein at high X-ray doses. As a result, diffraction patterns deteriorate with the increased absorbed dose. Several strategies such as sample freezing or scavenging of X-ray-generated free radicals are currently employed to minimize this damage. However, little is known about how the absorbed X-ray dose affects time-resolved Laue data collected at physiological temperatures where the protein is fully functional in the crystal, and how the kinetic analysis of such data depends on the absorbed dose. Here, direct evidence for the impact of radiation damage on the function of a protein is presented using time-resolved macromolecular crystallography. The effect of radiation damage on the kinetic analysis of time-resolved X-ray data is also explored.
PMCID: PMC3284346  PMID: 22338689
radiation damage; X-ray dose; room temperature; time-resolved crystallography; Laue crystallography
11.  Multi-crystal anomalous diffraction for low-resolution macromolecular phasing 
Anomalous diffraction signals can be very weak and sensitive to radiation damage. Here, in application to a poorly diffracting (d min of 3.5 Å) and relatively large structure (1456 ordered residues), it is shown that data merged from multiple crystals can support SAD structure determination when no single data set is adequate.
Multiwavelength anomalous diffraction (MAD) and single-wavelength anomalous diffraction (SAD) are the two most commonly used methods for de novo determination of macromolecular structures. Both methods rely on the accurate extraction of anomalous signals; however, because of factors such as poor intrinsic order, radiation damage, inadequate anomalous scatterers, poor diffraction quality and other noise-causing factors, the anomalous signal from a single crystal is not always good enough for structure solution. In this study, procedures for extracting more accurate anomalous signals by merging data from multiple crystals are devised and tested. SAD phasing tests were made with a relatively large (1456 ordered residues) poorly diffracting (d min = 3.5 Å) selenomethionyl protein (20 Se). It is quantified that the anomalous signal, success in substructure determination and accuracy of phases and electron-density maps all improve with an increase in the number of crystals used in merging. Structure solutions are possible when no single crystal can support structural analysis. It is proposed that such multi-crystal strategies may be broadly useful when only weak anomalous signals are available.
PMCID: PMC3016016  PMID: 21206061
anomalous scattering; MAD; multiple crystals; phase determination; SAD
12.  The plug-based nanovolume Microcapillary Protein Crystallization System (MPCS) 
The Microcapillary Protein Crystallization System (MPCS) is a new protein-crystallization technology used to generate nanolitre-sized crystallization experiments for crystal screening and optimization. Using the MPCS, diffraction-ready crystals were grown in the plastic MPCS CrystalCard and were used to solve the structure of methionine-R-sulfoxide reductase.
The Microcapillary Protein Crystallization System (MPCS) embodies a new semi-automated plug-based crystallization technology which enables nanolitre-volume screening of crystallization conditions in a plasticware format that allows crystals to be easily removed for traditional cryoprotection and X-ray diffraction data collection. Protein crystals grown in these plastic devices can be directly subjected to in situ X-ray diffraction studies. The MPCS integrates the formulation of crystallization cocktails with the preparation of the crystallization experiments. Within microfluidic Teflon tubing or the microfluidic circuitry of a plastic CrystalCard, ∼10–20 nl volume droplets are generated, each representing a microbatch-style crystallization experiment with a different chemical composition. The entire protein sample is utilized in crystallization experiments. Sparse-matrix screening and chemical gradient screening can be combined in one com­prehensive ‘hybrid’ crystallization trial. The technology lends itself well to optimization by high-granularity gradient screening using optimization reagents such as precipitation agents, ligands or cryoprotectants.
PMCID: PMC2585160  PMID: 19020349
protein crystallization; Microcapillary Protein Crystallization System
13.  Robust structural analysis of native biological macromolecules from multi-crystal anomalous diffraction data 
Anomalous diffraction signals from typical native macromolecules are very weak, frustrating their use in structure determination. Here, native SAD procedures are described for enhancing the signal to noise in anomalous diffraction by using multiple crystals are described. Five applications demonstrate that truly routine structure determination is possible without the need for heavy atoms.
Structure determinations for biological macromolecules that have no known structural antecedents typically involve the incorporation of heavier atoms than those found natively in biological molecules. Currently, selenomethionyl proteins analyzed using single- or multi-wavelength anomalous diffraction (SAD or MAD) data predominate for such de novo analyses. Naturally occurring metal ions such as zinc or iron often suffice in MAD or SAD experiments, and sulfur SAD has been an option since it was first demonstrated using crambin 30 years ago; however, SAD analyses of structures containing only light atoms (Z max ≤ 20) have not been common. Here, robust procedures for enhancing the signal to noise in measurements of anomalous diffraction by combining data collected from several crystals at a lower than usual X-ray energy are described. This multi-crystal native SAD method was applied in five structure determinations, using between five and 13 crystals to determine substructures of between four and 52 anomalous scatterers (Z ≤ 20) and then the full structures ranging from 127 to 1200 ordered residues per asymmetric unit at resolutions from 2.3 to 2.8 Å. Tests were devised to assure that all of the crystals used were statistically equivalent. Elemental identities for Ca, Cl, S, P and Mg were proven by f′′ scattering-factor refinements. The procedures are robust, indicating that truly routine structure determination of typical native macromolecules is realised. Synchrotron beamlines that are optimized for low-energy X-ray diffraction measurements will facilitate such direct structural analysis.
PMCID: PMC3689535  PMID: 23793158
anomalous scattering; multiple crystals; phase determination; sulfur SAD
14.  Crystallization of dihydrodipicolinate synthase from a clinical isolate of Streptococcus pneumoniae  
The emergence of drug-resistant bacteria highlights the importance of identifying potential drug targets. Dihydrodipicolinate synthase (DHDPS) is a valid but as yet unexploited antimicrobial target that functions in the biosynthesis of (S)-lysine. In this study, the cloning, expression, purification, crystallization and preliminary X-ray diffraction analysis of DHDPS from S. pneumoniae are described.
Dihydrodipicolinate synthase (DHDPS; EC catalyzes the rate-limiting step in the (S)-lysine biosynthesis pathway of bacteria and plants. Here, the cloning of the DHDPS gene from a clinical isolate of Streptococcus pneumoniae (OXC141 strain) and the strategy used to express, purify and crystallize the recombinant enzyme are described. Diffracting crystals were grown in high-molecular-weight PEG precipitants using the hanging-drop vapour-diffusion method. The best crystal, from which data were collected, diffracted to beyond 2.0 Å resolution. Initially, the crystals were thought to belong to space group P42212, with unit-cell parameters a = 105.5, b = 105.5, c = 62.4 Å. However, the R factors remained high following initial processing of the data. It was subsequently shown that the data set was twinned and it was thus reprocessed in space group P2, resulting in a significant reduction in the R factors. Determination of the structure will provide insight into the design of novel antimicrobial agents targeting this important enzyme from S. pneumoniae.
PMCID: PMC2805531  PMID: 20057065
antimicrobials; antibiotic resistance; dihydrodipicolinate synthase; lysine biosynthesis; Streptococcus pneumoniae
15.  Reduction of density-modification bias by β correction 
A cross-validation-based method for bias reduction in ‘classical’ iterative density modification of experimental X-ray crystallography maps provides significantly more accurate phase-quality estimates and leads to improved automated model building.
Density modification often suffers from an overestimation of phase quality, as seen by escalated figures of merit. A new cross-validation-based method to address this estimation bias by applying a bias-correction parameter ‘β’ to maximum-likelihood phase-combination functions is proposed. In tests on over 100 single-wavelength anomalous diffraction data sets, the method is shown to produce much more reliable figures of merit and improved electron-density maps. Furthermore, significantly better results are obtained in automated model building iterated with phased refinement using the more accurate phase probability parameters from density modification.
PMCID: PMC3069750  PMID: 21460453
reliable figure-of-merit estimates; density modification; maximum likelihood; bias reduction
16.  Evolutionary tabu search strategies for the simultaneous registration of multiple atomic structures in cryo-EM reconstructions 
Journal of structural biology  2010;170(1):164-171.
A structural characterization of multi-component cellular assemblies is essential to explain the mechanisms governing biological function. Macromolecular architectures may be revealed by integrating information collected from various biophysical sources - for instance, by intepreting low-resolution electron cryomicroscopy reconstructions in relation to the crystal structures of the constituent fragments. A simultaneous registration of multiple components is beneficial when building atomic models as it introduces additional spatial constraints to facilitate the native placement inside the map. The high-dimensional nature of such a search problem prevents the exhaustive exploration of all possible solutions. Here we introduce a novel method based on genetic algorithms, for the effcient exploration of the multi-body registration search space. The classic scheme of a genetic algorithm was enhanced with new genetic operations, tabu search and parallel computing strategies and validated on a benchmark of synthetic and experimental cryo-EM datasets. Even at a low level of detail, for example 35–40Å, the technique successfully registered multiple component biomolecules, measuring accuracies within one order of magnitude of the nominal resolutions of the maps. The algorithm was implemented using the Sculptor molecular modeling framework, which also provides a user-friendly graphical interface and enables an instantaneous, visual exploration of intermediate solutions.
PMCID: PMC2872094  PMID: 20056148
simultaneous registration; multi-body registration; multicomponent; macromolecular assembly; cryo-electron microscopy; cryo-EM; multi-resolution modeling; genetic algorithms; tabu search
17.  Structures from Anomalous Diffraction of Native Biological Macromolecules 
Science (New York, N.Y.)  2012;336(6084):1033-1037.
Crystal structure analyses for biological macromolecules without known structural relatives entail solving the crystallographic phase problem. Typical de novo phase evaluations depend on incorporating heavier atoms than those found natively; most commonly, multi- or single-wavelength anomalous diffraction (MAD or SAD) experiments exploit selenomethionyl proteins. Here we realize routine structure determination using intrinsic anomalous scattering from native macromolecules. We devised robust procedures for enhancing signal-to-noise in the slight anomalous scattering from generic native structures by combining data measured from multiple crystals at lower-than-usual x-ray energy. Using this multi-crystal SAD method (5–13 equivalent crystals), we determined structures at modest resolution (2.8Å-2.3Å) for native proteins varying in size (127–1148 unique residues) and number of sulfur sites (3–28). With no requirement for heavy-atom incorporation, such experiments provide an attractive alternative to selenomethionyl SAD experiments.
PMCID: PMC3769101  PMID: 22628655
18.  Purification, crystallization and preliminary crystallographic analysis of the catalytic domain of the extracellular cellulase CBHI from Trichoderma harzianum  
The catalytic domain of CHBI was purified from a cellular extract of T. harzianum. Diffraction-quality crystals were obtained and a native X-ray data set was collected using a synchrotron source.
The filamentous fungus Trichoderma harzianum has a considerable cellulolytic activity that is mediated by a complex of enzymes which are essential for the hydrolysis of microcrystalline cellulose. These enzymes were produced by the induction of T. harzianum with microcrystalline cellulose (Avicel) under submerged fermentation in a bioreactor. The catalytic core domain (CCD) of cellobiohydrolase I (CBHI) was purified from the extracellular extracts and submitted to robotic crystallization. Diffraction-quality CBHI CCD crystals were grown and an X-ray diffraction data set was collected under cryogenic conditions using a synchrotron-radiation source.
PMCID: PMC2935222  PMID: 20823521
cellobiohydrolases; Trichoderma harzianum; cellulases
19.  Purification, crystallization and preliminary crystallographic analysis of peroxidase from the palm tree Chamaerops excelsa  
Diffraction-quality crystals of the peroxidase from the palm tree C. excelsa were obtained and a native X-ray diffraction data set was collected at a synchrotron source.
Plant peroxidases are presently used extensively in a wide range of bio­technological applications owing to their high environmental and thermal stability. As part of efforts towards the discovery of appealing new biotechnological enzymes, the peroxidase from leaves of the palm tree Chamaerops excelsa (CEP) was extracted, purified and crystallized in its native form. An X-­ray diffraction data set was collected at a synchrotron source and data analysis showed that the CEP crystals belonged to the orthorhombic space group P212121, with unit-cell parameters a = 70.2, b = 100.7, c = 132.3 Å.
PMCID: PMC3232160  PMID: 22139187
palm trees; peroxidases; Chamaerops excelsa; extremoenzymes
20.  Autotracing of Escherichia coli acetate CoA-transferase α-subunit structure using 3.4 Å MAD and 1.9 Å native data 
The automation of protein structure determination is an essential component for high-throughput structural analysis in protein X-ray crystallography and is a key element in structural genomics. This highly challenging undertaking relies at present on the availability of high-quality native and derivatized protein crystals diffracting to high or moderate resolution, respectively. Obtaining such crystals often requires significant effort. The present study demonstrates that phases obtained at low resolution (>3.0 Å) from crystals of SeMet-labeled protein can be successfully used for automated structure determination. The crystal structure of acetate CoA-transferase α-subunit was solved using 3.4 Å multiwavelength anomalous dispersion data collected from a crystal containing SeMet-substituted protein and 1.9 Å data collected from a native protein crystal.
PMCID: PMC2792021  PMID: 12454473
21.  De-icing: recovery of diffraction intensities in the presence of ice rings 
Correction for ice-rings in diffraction images is demonstrated as an alternative to exclusion of affected reflections. Completeness can be increased without significant loss of quality in the integrated data.
Macromolecular structures are routinely determined at cryotemperatures using samples flash-cooled in the presence of cryoprotectants. However, sometimes the best diffraction is obtained under conditions where ice formation is not completely ablated, with the result that characteristic ice rings are superimposed on the macromolecular diffraction. In data processing, the reflections that are most affected by the ice rings are usually excluded. Here, an alternative approach of subtracting the ice diffraction is tested. High completeness can be retained with little adverse effect upon the quality of the integrated data. This offers an alternate strategy when high levels of cryoprotectant lead to loss of crystal quality.
PMCID: PMC2879358  PMID: 20516627
cryotemperatures; data collection; data processing; ice rings; DeIce
22.  Improvements toward highly accurate diffraction experiments at the macromolecular micro-crystallography beamline BL-17A 
Journal of Synchrotron Radiation  2013;20(Pt 6):938-942.
The BL-17A macromolecular crystallography beamline at the Photon Factory was updated to improve the accuracy of diffraction experiments conducted using tiny crystals.
BL-17A is a macromolecular crystallography beamline dedicated to diffraction experiments conducted using micro-crystals and structure determination studies using a lower energy X-ray beam. In these experiments, highly accurate diffraction intensity measurements are definitively important. Since this beamline was constructed, the beamline apparatus has been improved in several ways to enable the collection of accurate diffraction data. The stability of the beam intensities at the sample position was recently improved by modifying the monochromator. The diffractometer has also been improved. A new detector table was installed to prevent distortions in the diffractometer’s base during the repositioning of the diffractometer detector. A new pinhole system and an on-axis viewing system were installed to improve the X-ray beam profile at the sample position and the centering of tiny crystal samples.
PMCID: PMC3795560  PMID: 24121344
macromolecular crystallography; beamline
23.  Crystallization of recombinant bifunctional nuclease TBN1 from tomato 
Glycosylated recombinant bifunctional nuclease from tomato has been crystallized and preliminary X-ray diffraction analysis was performed.
The endonuclease TBN1 from Solanum lycopersicum (tomato) was expressed in Nicotiana benthamiana leaves and purified with suitable quality and in suitable quantities for crystallization experiments. Two crystal forms (orthorhombic and rhombohedral) were obtained and X-ray diffraction experiments were performed. The presence of natively bound Zn2+ ions was confirmed by X-ray fluorescence and by an absorption-edge scan. X-ray diffraction data were collected from the orthorhombic (resolution of 5.2 Å) and rhombohedral (best resolution of 3.2 Å) crystal forms. SAD, MAD and MR methods were applied for solution of the phase problem, with partial success. TBN1 contains three Zn2+ ions in a similar spatial arrangement to that observed in nuclease P1 from Penicillium citrinum.
PMCID: PMC3079990  PMID: 21206042
plant endonucleases; cancer; antitumour activity; MAD
24.  Carrying out an optimal experiment 
Diffraction data collection parameters leading to optimal data quality are discussed in the context of different applications of these data.
Diffraction data collection is the last experimental stage in structural crystallography. It has several technical and theor­etical aspects and a compromise usually has to be found between various parameters in order to achieve optimal data quality. The influence and importance of various experimental parameters and their consequences are discussed in the context of different data applications, such as molecular replacement, anomalous phasing, high-resolution refinement or searching for ligands.
PMCID: PMC2852303  PMID: 20382992
diffraction data collection; data-collection strategies; diffraction experiments
25.  X-CHIP: an integrated platform for high-throughput protein crystallization and on-the-chip X-ray diffraction data collection 
The X-CHIP (X-ray Crystallography High-throughput Integrated Platform) is a novel microchip that has been developed to combine multiple steps of the crystallographic pipeline from crystallization to diffraction data collection on a single device to streamline the entire process.
The X-CHIP (X-ray Crystallization High-throughput Integrated Platform) is a novel microchip that has been developed to combine multiple steps of the crystallographic pipeline from crystallization to diffraction data collection on a single device to streamline the entire process. The system has been designed for crystallization condition screening, visual crystal inspection, initial X-ray screening and data collection in a high-throughput fashion. X-ray diffraction data acquisition can be performed directly on-the-chip at room temperature using an in situ approach. The capabilities of the chip eliminate the necessity for manual crystal handling and cryoprotection of crystal samples, while allowing data collection from multiple crystals in the same drop. This technology would be especially beneficial for projects with large volumes of data, such as protein-complex studies and fragment-based screening. The platform employs hydrophilic and hydrophobic concentric ring surfaces on a miniature plate transparent to visible light and X-rays to create a well defined and stable microbatch crystallization environment. The results of crystallization and data-collection experiments demonstrate that high-quality well diffracting crystals can be grown and high-resolution diffraction data sets can be collected using this technology. Furthermore, the quality of a single-wavelength anomalous dispersion data set collected with the X-CHIP at room temperature was sufficient to generate interpretable electron-density maps. This technology is highly resource-efficient owing to the use of nanolitre-scale drop volumes. It does not require any modification for most in-house and synchrotron beamline systems and offers a promising opportunity for full automation of the X-ray structure-determination process.
PMCID: PMC3107051  PMID: 21636893
protein crystallization devices; in situ X-ray analysis; crystallization; crystal visual inspection; diffraction data collection

Results 1-25 (895550)