Проблемы технической оснащённости России для работы в условиях Арктики

Cytochrome c oxidase is a respiratory enzyme catalysing the energy-conserving reduction of molecular oxygen to water. The crystal structure of the ba(3)-cytochrome c oxidase from Thermus thermophilus has been determined to 2.4 Å resolution using multiple anomalous dispersion (MAD) phasing and led to the discovery of a novel subunit IIa. A structure-based sequence alignment of this phylogenetically very distant oxidase with the other structurally known cytochrome oxidases leads to the identification of sequence motifs and residues that seem to be indispensable for the function of the haem copper oxidases, e.g. a new electron transfer pathway leading directly from Cu(A) to Cu(B). Specific features of the ba(3)-oxidase include an extended oxygen input channel, which leads directly to the active site, the presence of only one oxygen atom (O(2–), OH(–) or H(2)O) as bridging ligand at the active site and the mainly hydrophobic character of the interactions that stabilize the electron transfer complex between this oxidase and its substrate cytochrome c. New aspects of the proton pumping mechanism could be identified

Предельные метрологические характеристики генераторов сигналов на основе прямого цифрового синтеза

Выпускная квалификационная работа 75 страниц, 24 рисунка, 26 таблиц, 16 источников, 4 приложения. Ключевые слова: генератор сигналов, метрологические характеристики, амплитуда, период, коэффициент гармоник. Объектами исследования являются характеристики гармонических колебаний: амплитуда, период и коэффициент гармоник. Цель работы – исследование метрологических характеристик генераторов сигналов на основе прямого цифрового синтеза. В ходе работы проводилось определение нестабильности амплитуды, нестабильности периода и коэффициента гармоник путем моделирования с помощью программного обеспечения для инженерных вычислений – Mathcad. В результате работы были получены зависимости, позволяющие оценить необходимый период дискретизации по заданной нестабильности амплитуды, нестабильности периодаFinal qualifying work is 75 pages, 24 figures, 26 tables, 16 sources, 4 of the annex. Keywords: signal generator, the metrological characteristics, amplitude, period, total harmonic distortion. The objects of study are the characteristics of harmonic vibrations: amplitude, period, and total harmonic distortion. The purpose is research of metrological characteristics signal generator based on direct digital synthesis. The work was carried out determining the amplitude of instability, instability period and harmonic distortion by simulation software for engineering calculations - Mathcad. As a result of the work were obtained according to assess the required sampling period for a given amplitude instability, instability period and harmonic distortion

Extraction of single bunches of synchrotron radiation from storage rings with an X-ray chopper based on a rotating mirror

An ultrafast shutter has been developed for alteration of the time structure of synchrotron radiation from storage rings in the hard X-ray regime. In test applications on the wiggler beamline BW6 at DORIS, single bunches were extracted from the incident pulsed synchrotron radiation with minimum bunch-to-bunch distances of 482 ns. Even substantially shorter time windows may be defined in the case of tight collimation in the incident beam, e.g. on low-emittance sources. The shutter system is based on a new chopper concept involving a rotating X-ray mirror which totally reflects the incident radiation onto the sample through a remote slit. Rather low rotational velocities are sufficient to reach extremely short full open times. An additional shutter consisting of a slowly rotating disk prevents frame overlap and controls the repetition rate. A coincidence timing circuit checks the synchronization with the synchrotron bunch clock and provides trigger signals, e.g. for external excitation of a sample. The chopper system may be used, for example, in nanosecond time-resolved Laue diffraction experiments

Beamline diagnostics for protein crystallography using synchrotron radiation

Beam diagnostics devices are described for the monitoring of all basic parameters relevant to protein data collection using synchrotron radiation. The parameters include the total power in the white beam, the positions and directions of the incident white and monochromatic beams, and the intensity, wavelength, and polarization in the incident monochromatic beam. Such devices have been installed on a doubly focusing wiggler beamline, BW6, at DORIS. They assure high quality in protein data collection despite fluctuations in the beam, facilitate rapid alignment of the entire beamline, and provide a basis for automatic realignment of the diffraction setup and the x‐ray optics

The Essential Function of HP1β\beta: A Case of the Tail Wagging the Dog?

A large body of work in various organisms has shown that the presence of HP1 structural proteins and methylated lysine 9 of histone H3 (H3K9me) represent the characteristic hallmarks of heterochromatin. We propose that a more critical assessment of the physiological importance of the H3K9me-HP1 interaction is warranted in light of recent studies on the mammalian HP1 beta protein. Based on this new research, we conclude that the essential function of HP1 beta (and perhaps that of its orthologues in other species) lies outside the canonical heterochromatic H3K9me-HP1 interaction. We suggest instead that binding of a small fraction of HP1 beta to the H3 histone fold performs a critical role in heterochromatin function and organismal survival

A Steric Mechanism for Inhibition of CO Binding to Heme Proteins

The crystal structures of myoglobin in the deoxy- and carbon monoxide–ligated states at a resolution of 1.15 angstroms show that carbon monoxide binding at ambient temperatures requires concerted motions of the heme, the iron, and helices E and F for relief of steric inhibition. These steps constitute the main mechanism by which heme proteins lower the affinity of the heme group for the toxic ligand carbon monoxide

Investigations on the Maturation and Regulation of Archaebacterial Proteasomes

The 20 S proteasome (core particle, CP) is a multifunctional protease complex and composed of four heptameric subunit rings arranged in a hollow, barrel-shaped structure. Here, we report the crystal structure of the CP from Archaeoglobus fulgidus at 2.25 Å resolution. The analysis of the structure of early and late assembly intermediates of this CP gives new insights in the maturation of archaebacterial CPs and indicates similarities to assembly intermediates observed in eukaryotes. We also show a striking difference in mechanism and regulation of substrate access between eukaryotic and archaebacterial 20 S proteasomes. While eukaryotic CPs are auto-inhibited by the N-terminal tails of the outer α-ring by imposing topological closure with a characteristic sequence motif (YDR-motif) and show regulatory gating this segment is disordered in the CP and differently structured in the α7-sub-complex of A. fulgidus leaving a pore leading into the particle with a diameter of 13 Å. Mutagenesis and functional studies indicate the absence of regulatory gating in the archaeal 20 S proteasome

X-ray structure at 1.76 Å resolution of a polypeptide phospholipase A2\mathrm{A_2} Inhibitor

The high resolution crystal structure of a natural PLA2 inhibitor has been determined by Patterson search methods. In the heterodimeric, neurotoxic complex, vipoxin, isolated from the venom of Bulgarian viper, PLA2 inhibitor represents the non-toxic subunit. The model was refined to a crystallographic R-factor of 15.5% for data between 6 and 1.76 Å resolution. The packing of the inhibitor in the crystal reveals close contacts between the molecules, which are symmetry-related by the 2-fold axes of the lattice. These pairs associate as a crystallographic dimer, stabilized by a set of interactions, including van der Waals contacts between residues from symmetry-related pairs, denoted as the recognition site and the recognition surface. Residues Ph3, Trp31 and Tyr119 represent the recognition site of inhibitor which possibly fits to the hydrophobic wall of the target PLA2. The topology of the inhibitor represents the PLA2 type of folding: three long helices and a β-hairpin. Superposition of the structure of the inhibitor shows an almost complete overlap with different mammalian and viper PLA2 in the backbone and in the position of the side-chains of the residues that belong to the active centre and the hydrophobic wall. A “lock and key” mechanism of recognition of its native PLA2 in gland cells and other toxic PLA2 in vitro has been suggested. The mechanism includes complementary “head to tail” interactions between the recognition site of the inhibitor and a recognition surface located on the hydrophobic wall of the target PLA2. Having a high spatial homology with the PLA2 family of enzymes but opposing their action, the inhibitor from vipoxin presents an example of a divergent evolution of an ancient PLA2. The presence of a space for binding calcium in the inhibitor is believed to be a rudiment and proof of a common origin with PLA2