Universal Microwave Photonics Approach to Frequency-Coded Quantum Key Distribution

Design principles of universal microwave photonics system (MPS) for quantum key distribution (QKD) with frequency coding are concerned. Its main modulation concept lies in single photon generation on sidebands of optical carrier and determination of photons ground state through its registration and the amplitude value of its carrier frequency as reference channel. So, it is necessary to solve problems of signal-to-carrier ratio of single photon detector (SPD) and aspects of photon number splitting (PNS) attack, nonlinear phase modulation (NPM) between carrier and sidebands in fiber, and finally, spectral selection of carrier in receiver. The technologies, based on the modulation conversion of an optical carrier, are widely used in microwave photonics. Due to the natural symmetry of modulated signals and the highest achievable ratio of the modulation conversions, amplitude-phase modulation with complete or partial suppression of the optical carrier has found a particularly wide application in MPS. The characteristics of advanced MPS for QKD with frequency coding and carrier suppression based on tandem amplitude modulation and phase commutation are presented. New systems can have classical symmetric or non-classical asymmetric structure for QKD based only on spectral selection of carrier and subcarriers without re-modulation

Influence of parameters of delayed asphalt coking process on yield and quality of liquid and solid-phase products

Paper studies the effect of excess pressure during delayed coking of asphalt, obtained by propane deasphaltization of tar, on yield and physical and chemical properties of hydrocarbon fuels' components and solid-phase product – petroleum coke. Asphalt was coked at a temperature of 500 °C and excess pressure of 0.15-0.35 MPa in a laboratory unit for delayed coking of periodic action. Physical and chemical properties of raw materials and components of light (gasoline), medium (light gasoil), and heavy (heavy gasoil) distillates obtained during experimental study were determined: density, viscosity, coking ability, sulfur content, iodine number, pour points, flash points, fluidity loss and fractional composition. Quantitative group hydrocarbon and microelement compositions and properties of obtained samples of petroleum coke (humidity, ash content, volatiles' yield, sulfur content, etc.) were also studied. Comparative assessment of their quality is given in accordance with requirements of GOST 22898-78 “Low-sulfur petroleum coke. Specifications”. In addition, patterns of changes in excess coking pressure on yield and quality indicators of distillate products and petroleum coke were revealed. With an increase in excess pressure of coking process from 0.15 to 0.35 MPa, content of paraffin-naphthenic hydrocarbons in light and heavy gasoils of delayed coking  decreases. Common pattern in asphalt coking is an increase in yield of coke and hydrocarbon gas with an increase in excess pressure from 0.15 to 0.35 MPa

Mechanism of ribosome shutdown by RsfS in Staphylococcus aureus revealed by integrative structural biology approach.

Funder: The Russian Government Program of Competitive Growth of Kazan Federal UniversityFor the sake of energy preservation, bacteria, upon transition to stationary phase, tone down their protein synthesis. This process is favored by the reversible binding of small stress-induced proteins to the ribosome to prevent unnecessary translation. One example is the conserved bacterial ribosome silencing factor (RsfS) that binds to uL14 protein onto the large ribosomal subunit and prevents its association with the small subunit. Here we describe the binding mode of Staphylococcus aureus RsfS to the large ribosomal subunit and present a 3.2 Å resolution cryo-EM reconstruction of the 50S-RsfS complex together with the crystal structure of uL14-RsfS complex solved at 2.3 Å resolution. The understanding of the detailed landscape of RsfS-uL14 interactions within the ribosome shed light on the mechanism of ribosome shutdown in the human pathogen S. aureus and might deliver a novel target for pharmacological drug development and treatment of bacterial infections

Structural basis of ABCF-mediated resistance to pleuromutilin, lincosamide, and streptogramin A antibiotics in Gram-positive pathogens

he antibiotic target. One class of such proteins are the antibiotic resistance (ARE) ATP-binding cassette (ABC) proteins of the F-subtype (ARE-ABCFs), which are widely distributed throughout Gram-positive bacteria and bind the ribosome to alleviate translational inhibition from antibiotics that target the large ribosomal subunit. Here, we present single-particle cryo-EM structures of ARE-ABCF-ribosome complexes from three Gram-positive pathogens: Enterococcus faecalis LsaA, Staphylococcus haemolyticus VgaALC and Listeria monocytogenes VgaL. Supported by extensive mutagenesis analysis, these structures enable a general model for antibiotic resistance mediated by these ARE-ABCFs to be proposed. In this model, ABCF binding to the antibiotic-stalled ribosome mediates antibiotic release via mechanistically diverse long-range conformational relays that converge on a few conserved ribosomal RNA nucleotides located at the peptidyltransferase center. These insights are important for the future development of antibiotics that overcome such target protection resistance mechanisms

Engineering the Catalytic Properties of Two Domain Laccase from Streptomyces griseoflavus Ac 993

Laccases catalyze the oxidation of substrates with the concomitant reduction of oxygen to water. Recently, we found that polar residues located in tunnels leading to Cu2 and Cu3 ions control oxygen entrance His 165 and proton transport Arg 240 of two domain laccase 2D from Streptomyces griseoflavus SgfSL . In this work, we have focused on optimizing the substrate binding pocket SBP of SgfSL while simultaneously adjusting the oxygen reduction process. SgfSL variants with three single Met199Ala, Met199Gly, and Tyr230Ala and three double amino acid residues substitutions Met199Gly His165Ala, His165Ala Arg240His, Met199Gly Arg240His were constructed, purified, and investigated. Combination of substitutions in the SBP and in the tunnel leading to Cu2 ion Met199Gly Arg240His increased SgfSL catalytic activity towards ABTS by 5 fold, and towards 2.6 DMP by 16 fold. The high activity of the Met199Gly Arg240His variant can be explained by the combined effect of the SBP geometry optimization Met199Gly and increased proton flux via the tunnel leading to Cu2 ion Arg240His . Moreover, the variant with Met199Gly and His165Ala mutations did not significantly increase SgfSL s activity, but led to a drastic shift in the optimal pH of 2.6 DMP oxidation. These results indicate that His 165 not only regulates oxygen access, but it also participates in proton transport in 2D laccase

Crystallization and X ray diffraction studies of a two domain laccase from Streptomyces griseoflavus

Laccase (EC 1.10.3.2) is one of the most common copper-containing oxidases; it is found in many organisms and catalyzes the oxidation of primarily phenolic compounds by oxygen. Two-domain laccases have unusual thermostability, resistance to inhibitors and an alkaline optimum of activity. The causes of these properties in two-domain laccases are poorly understood. A recombinant two-domain laccase (SgfSL) was cloned from the genome of Streptomyces griseoflavus Ac-993, expressed in Escherichia coli and purified to homogeneity. The crystals of SgfSL belonged to the monoclinic space group P2(1), with unit-cell parameters a = 74.64, b = 94.72, c = 117.40 Å, β = 90.672°, and diffraction data were collected to 2.0 Å resolution using a synchrotron-radiation source. Two functional trimers per asymmetric unit correspond to a Matthews coefficient of 1.99 Å(3) Da(−1) according to the monomer molecular weight of 35.6 kDa

Novel approaches for the lipid sponge phase crystallization of the Rhodobacter sphaeroides photosynthetic reaction center

With the recent developments in the field of free electron laser based serial femtosecond crystallography, the necessity to obtain a large number of high quality crystals has emerged. In this work crystallization techniques were selected, tested and optimized for the lipid mesophase crystallization of the Rhodobacter sphaeroides membrane pigment protein complex, known as the photosynthetic reaction center RC . Novel approaches for lipid sponge phase crystallization in comparatively large volumes using Hamilton gas tight glass syringes and plastic pipetting tips are described. An analysis of RC crystal structures obtained by lipid mesophase crystallization revealed non native ligands that displaced the native electron transfer cofactors carotenoid sphero idene and a ubi quinone molecule from their binding pockets. These ligands were identified and were found to be lipids that are major mesophase components. The selection of distinct co crystallization conditions with the missing cofactors facilitated the restoration of sphero idene in its binding sit

The role of positive charged residue in the proton transfer mechanism of two domain laccase from Streptomyces griseoflavus Ac 993

Multi copper oxidases are capable of coupling the one electron oxidation of four substrate equivalents to the four electron reduction of dioxygen to two molecules of water. This process takes place at the trinuclear copper center of the enzymes. Previously, the main catalytic stages for three domain 3D laccases have been identified. However, for bacterial small two domain 2D laccases several questions remain to be answered. One of them is the nature of the protonation events upon the reductive cleavage of dioxygen to water. In 3D laccases, acidic residues play a key role in the protonation mechanisms. In this study, the role of the Arg240 residue, located within the T2 tunnel of 2D laccase from Streptomyces griseoflavus Ac 993, was investigated. X ray structural analysis and kinetic characterization of two mutants, R240A and R240H, have provided support for a role of this residue in the protonation event

Numerical simulation of oil spills based on the GNOME and ADIOS

The Exxon Valdez oil spill emergency has shown that simulation of oil spills trajectory is the main action in planning response measures. Modeling the trajectory of the oil slick allows predicting in advance the direction of the motion of the stain, the time it will take to reach the shore and assess the possible environmental consequences for the contaminated coastal zone. In this paper, the Exxon Valdez oil spill trajectory was analyzed using two different models, the GNOME model and the HAZAT trajectory model. Conclusions are drawn about the reasons for the differences in the results provided by the two models. The accuracy of the simulation is strongly related to the input of geographic and meteorological data. In addition, ADIOS software was used to predict the weathering process of the modeled emergency event. It was found that the main factors influencing the change in the physical and chemical characteristics of oil dispersed in the water body are the wind speed and direction, water temperature and wave height