[Show abstract][Hide abstract] ABSTRACT: Here, an automated procedure is described to identify the positions of many cryocooled crystals mounted on the same sample holder, to rapidly predict and rank their relative diffraction strengths and to collect partial X-ray diffraction data sets from as many of the crystals as desired. Subsequent hierarchical cluster analysis then allows the best combination of partial data sets, optimizing the quality of the final data set obtained. The results of applying the method developed to various systems and scenarios including the compilation of a complete data set from tiny crystals of the membrane protein bacteriorhodopsin and the collection of data sets for successful structure determination using the single-wavelength anomalous dispersion technique are also presented.
Full-text · Article · Nov 2015 · Acta Crystallographica Section D Biological Crystallography
[Show abstract][Hide abstract] ABSTRACT: Whether long-range quantum coherent states could exist in biological systems, and beyond low-temperature regimes where quantum physics is known to be applicable, has been the subject to debate for decades. It was proposed by Fröhlich that vibrational modes within protein molecules can order and condense into a lowest-frequency vibrational mode in a process similar to Bose-Einstein condensation, and thus that macroscopic coherence could potentially be observed in biological systems. Despite the prediction of these so-called Fröhlich condensates almost five decades ago, experimental evidence thereof has been lacking. Here, we present the first experimental observation of Fröhlich condensation in a protein
structure. To that end, and to overcome the challenges associated with probing low-frequency molecular vibrations in proteins (which has hampered understanding of their role in proteins' function), we combined terahertz techniques with a highly sensitive X-ray crystallographic method to visualize low-frequency vibrational modes in the protein
structure of hen-egg white lysozyme. We found that 0.4 THz electromagnetic radiation induces non-thermal changes in electron density. In particular, we observed a local increase of electron density in a long α-helix motif consistent with a subtle longitudinal compression of the helix. These observed electron density changes occur at a low absorption rate indicating that thermalization of terahertz photons happens on a micro- to milli-second time scale, which is much slower than the expected nanosecond time scale due to damping of delocalized low frequency vibrations. Our analyses show that the micro- to milli-second lifetime of the vibration can only be explained by Fröhlich condensation, a phenomenon predicted almost half a century ago, yet never experimentally confirmed.
[Show abstract][Hide abstract] ABSTRACT: Isobutanol is deemed to be a next-generation biofuel and a renewable platform chemical.1 Non-natural biosynthetic pathways for isobutanol production have been implemented in cell-based and in vitro systems with Bacillus subtilis acetolactate synthase (AlsS) as key biocatalyst.2-6 AlsS catalyzes the condensation of two pyruvate molecules to acetolactate with thiamine diphosphate and Mg(2+) as cofactors. AlsS also catalyzes the conversion of 2-ketoisovalerate into isobutyraldehyde, the immediate precursor of isobutanol. Our phylogenetic analysis suggests that the ALS enzyme family forms a distinct subgroup of ThDP-dependent enzymes. To unravel catalytically relevant structure-function relationships, we solved the AlsS crystal structure at 2.3 Å in the presence of ThDP, Mg(2+) and in a transition state with a 2-lactyl moiety bound to ThDP. We supplemented our structural data by point mutations in the active site to identify catalytically important residues.
[Show abstract][Hide abstract] ABSTRACT: Peroxisomes are membrane-enclosed organelles in eukaryotic cells with important roles in lipid metabolism and the scavenging of reactive oxygen species. Peroxisomes are capable of carrying an unusually high load of proteins, which under appropriate nutrient conditions results in the in situ crystallization of peroxisomal proteins in several yeast species and vertebrate hepatocytes [1,2]. In the methylotrophic yeast H.polymorpha, the predominant peroxisomal protein alcohol/methanol oxidase (AO) oligomerizes into octameric assemblies with a molecular mass of 600 kDa that spontaneously form 200-500 nm crystallites within peroxisomes . We exposed H.polymorpha cell suspensions containing peroxisome-confined AO crystallites to femtosecond X-ray pulses at the Coherent X-ray Imaging (CXI) experimental endstation at the Linac Coherent Light Source. Peak detection routines mining the resulting scattering profiles identified >5000 Bragg-sampled diffraction patterns, providing the proof of concept that background scattering from the cells does not deteriorate the signal-to-noise ratio to an extent precluding observation of diffraction from individual AO crystallites. Summation patterns assembled from the individual frames match low-resolution powder diffraction patterns from concentrated suspensions of purified peroxisomes collected at the P14 beamline at the PETRAIII synchrotron, confirming that the observed diffraction mainly results from Bragg scattering of peroxisomal crystallites. To the best of our knowledge our data are the first to report room temperature X-ray diffraction from functional protein crystals in their native cellular environment. Currently the maximum resolution achieved in the diffraction patterns is limited to 20-15 Å. Future work will need to address improved sample preparation protocols in order to assess whether diffraction to a resolution sufficient to permit structure solution can be obtained. Protein crystal formation in vivo has been observed under physiological or pathological conditions in a number of other systems . We hope that our results will help to establish serial femtosecond X-ray diffraction (SFX) as a method for structural characterization of cellular structures with crystalline content and provide a proof of concept for using in situ crystallization of proteins as a means to generate nanocrystalline samples for SFX.
Full-text · Article · Aug 2014 · Acta Crystallographica Section A: Foundations and Advances
[Show abstract][Hide abstract] ABSTRACT: Protein crystallography continues to be one of the most frequently used techniques to obtain structural information of biomacromolecules to atomic resolution. Since protein crystals of delicate target systems are often limited in size, one of the main goals in the design of modern beamlines is the construction of highly intense X-ray beams with small focal size to obtain high resolution diffraction images of microcrystals. However, this development has led to the situation, that the full intensity of the beam can destroy a protein crystal within fractions of a second. Therefore often only a small number of diffraction patterns can be obtained from one single crystal. Here we describe the adaptation of the serial crystallography approach, which has first been developed at X-ray Free-Electron Lasers (Chapman et al. 2011) to the usage of a microfocus synchrotron beamline, using a standard cryogenic loop for sample delivery. We proved this concept with in vivo grown cathepsinB microcrystals (TbCatB, Koopmann et al. 2012, Redecke et al. 2013) (average of 9 μm3), a medically and pharmaceutically relevant protein, involved in the life cycle of T. brucei. In these experiments it was possible to show that serial crystallography enables the utilization and outcome of the above described bottlenecks and features of modern 3rd generation synchrotron microfocus beamlines. Our strategy exploits the combination of a micron-sized X-ray beam, high precision diffractometry and shutterless data acquisition with a pixel-array detector. By combining the data of 80 TbCatB crystals, it was possible to assemble a dataset to 3.0 Å resolution. The data allow the refinement of a structural model that is consistent with that previously obtained using FEL radiation, providing mutual validation.
Preview · Article · Aug 2014 · Acta Crystallographica Section A: Foundations and Advances
[Show abstract][Hide abstract] ABSTRACT: Since 2012, EMBL Hamburg operates two new beamlines for macromolecular crystallography - P13 and P14 - at PETRA III at DESY (Hamburg, Germany). We exploit the high brilliance and the wide energy range offered by PETRA III to offer a wide range of conditions to fit the experimental conditions to the challenges posed by the samples. P13 provides high photon flux down to 4 keV. With a helium cone and a kappa goniostat, this allows optimized data collection for SAD phasing. Using adaptive mirrors, the focus size (H x V) can be adjusted between 30 x 20 μm^2 and 150 x 100 μm^2 to match the size of the sample. A MARVIN sample changer is in operation for rapid loading and unloading of samples. P14 offers a high photon flux (>10^12 ph/sec at 12 keV into 5 x 5 µm^2). The beamsize can be varied between 1 x 1.5 mm^2 (unfocused) and 5 x 5 µm^2 (fully focused) in less than a minute by moving the KB mirrors in and out of the beam. For small crystals, an MD3 vertical diffractometer with a sphere of confusion smaller than 100 nm offers excellent conditions. Both beamlines are equipped with PILATUS 6M-F detectors for shutter-less data collection and dedicated data processing computers. The beamlines are embedded into the 'Integrated Facility for Structural Biology' offering facilities for sample preparation and characterization, a laboratory specifically equipped for the preparation of heavy atom derivatives, and downstream facilities for data evaluation We will report about the status of the beamlines and describe typical experimental situations (small crystals, large unit cells, serial crystallography, low-energy phasing, small molecules and others).
Preview · Article · Aug 2014 · Acta Crystallographica Section A: Foundations and Advances
[Show abstract][Hide abstract] ABSTRACT: Serial crystallography using X-ray free-electron lasers enables the collection of tens of thousands of measurements from an equal number of individual crystals, each of which can be smaller than 1 µm in size. This manuscript describes an alternative way of handling diffraction data recorded by serial femtosecond crystallography, by mapping the diffracted intensities into three-dimensional reciprocal space rather than integrating each image in two dimensions as in the classical approach. We call this procedure 'three-dimensional merging'. This procedure retains information about asymmetry in Bragg peaks and diffracted intensities between Bragg spots. This intensity distribution can be used to extract reflection intensities for structure determination and opens up novel avenues for post-refinement, while observed intensity between Bragg peaks and peak asymmetry are of potential use in novel direct phasing strategies.
Full-text · Article · Jul 2014 · Philosophical Transactions of The Royal Society B Biological Sciences
[Show abstract][Hide abstract] ABSTRACT: Crystal structure determinations of biological macromolecules are limited by the availability of sufficiently sized crystals and by the fact that crystal quality deteriorates during data collection owing to radiation damage. Exploiting a micrometre-sized X-ray beam, high-precision diffractometry and shutterless data acquisition with a pixel-array detector, a strategy for collecting data from many micrometre-sized crystals presented to an X-ray beam in a vitrified suspension is demonstrated. By combining diffraction data from 80
procathepsin B crystals with an average volume of 9 µm
, a complete data set to 3.0 Å resolution has been assembled. The data allowed the refinement of a structural model that is consistent with that previously obtained using free-electron laser radiation, providing mutual validation. Further improvements of the serial synchrotron crystallography technique and its combination with serial femtosecond crystallography are discussed that may allow the determination of high-resolution structures of micrometre-sized crystals.
[Show abstract][Hide abstract] ABSTRACT: Copper-containing ferroxidase ceruloplasmin (Cp) forms binary and ternary complexes with cationic proteins lactoferrin (Lf) and myeloperoxidase (Mpo) during inflammation. We present an X-ray crystal structure of a 2Cp-Mpo complex at 4.7 Å resolution. This structure allows one to identify major protein-protein interaction areas and provides an explanation for a competitive inhibition of Mpo by Cp and for the activation of p-phenylenediamine oxidation by Mpo. Small angle X-ray scattering was employed to construct low-resolution models of the Cp-Lf complex and, for the first time, of the ternary 2Cp-2Lf-Mpo complex in solution. The SAXS-based model of Cp-Lf supports the predicted 1∶1 stoichiometry of the complex and demonstrates that both lobes of Lf contact domains 1 and 6 of Cp. The 2Cp-2Lf-Mpo SAXS model reveals the absence of interaction between Mpo and Lf in the ternary complex, so Cp can serve as a mediator of protein interactions in complex architecture. Mpo protects antioxidant properties of Cp by isolating its sensitive loop from proteases. The latter is important for incorporation of Fe(3+) into Lf, which activates ferroxidase activity of Cp and precludes oxidation of Cp substrates. Our models provide the structural basis for possible regulatory role of these complexes in preventing iron-induced oxidative damage.
[Show abstract][Hide abstract] ABSTRACT: The radiation damage rates to crystals of 15 model macromolecular structures were studied using an automated radiation sensitivity characterization procedure. The diffracted intensity variation with dose is described by a two-parameter model. This model includes a strong resolution-independent decay specific to room-temperature measurements along with a linear increase in overall Debye–Waller factors. An equivalent representation of sensitivity
a single parameter, normalized half-dose, is introduced. This parameter varies by an order of magnitude between the different structures studied. The data show a correlation of crystal radiation sensitivity with crystal solvent content but no dose-rate dependency was detected in the range 0.05–300 kGy s
. The results of the crystal characterization are suitable for either optimal planning of room-temperature data collection or
crystallization plate screening experiments.
Full-text · Article · Jan 2013 · Journal of Synchrotron Radiation
[Show abstract][Hide abstract] ABSTRACT: Plastocyanin (PC) from poplar leaves is present in two isoforms, PCa and PCb, which differ in sequence by amino acid replacements at locations remote from the copper center and simultaneously act in the photosynthetic electron-transport chain. We describe ultra-high resolution structures of PCa and high-resolution structures of PCb, both under oxidizing and reducing conditions at pH 4, 6 and 8. The docking on cytochrome f and photosystem I, respectively, has been modeled for both isoforms. PCa and PCb exhibit closely similar overall and active-site structures, except for a difference in the relative orientation of the acidic patches. The isoforms exhibit substantial differences in the dependence of the reduced (Cu(I)) geometry on pH. In PCa, the decrease in pH causes a gradual dissociation of His87 from Cu(I) at low pH, probably adopting a neutral tautomeric state. In PCb, the histidine remains covalently bound to Cu(I) and may adopt a doubly protonated state at low pH. The fact that both isoforms have similar although not identical functions in photosynthetic electron flows suggests that the His87 imidazole does not play a crucial role for the pathway of electron transport from cytochrome f to oxidized PC.
No preview · Article · Jul 2012 · Journal of inorganic biochemistry
[Show abstract][Hide abstract] ABSTRACT: Slope measuring deflectometry has become a standard technique for inspection of
ultra-precise reflective optical elements of synchrotron applications.
We will report on the inspection of ultra-precise adaptive synchrotron mirrors (bimorph mirrors)
to be used under grazing incidence condition. The measurements were performed
at the BESSY-II Optics Laboratory (BOL) of the Helmholtz Zentrum Berlin (HZB)
using the Nanometer Optical Component Measuring Machine (NOM).
Based on the data obtained by the optical measurements, we simulate the characteristics
of the achievable X-ray focus by ray tracing calculations, demonstrated as follows in the case
of bimorph mirrors of the EMBL MX1 beamline for macromolecular crystallography
at DESY’s synchrotron radiation source PETRA III in Hamburg.
Full-text · Article · Jun 2012 · Measurement Science and Technology