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

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

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

High-resolution crystal structure of spectrin SH3 domain fused with a proline-rich peptide

A new chimeric protein, named WT-CIIA, was designed by connecting the proline-rich decapeptide PPPVPPYSAG to the C-terminus of the alpha-spectrin SH3 domain through a natural twelve-residue linker to obtain a single-chain model that would imitate intramolecular SH3-ligand interaction. The crystal structure of this fusion protein was determined at 1.7 Å resolution. The asymmetric unit of the crystal contained two SH3 globules contacting with one PPPVPPY fragment located between them. The domains are related by the two-fold non-crystallographic axis and the ligand lies in two opposite orientations with respect to the conservative binding sites of SH3 domains

Cryo-EM structure of the ribosome functional complex of the human pathogen Staphylococcus aureus at 3.2 Å resolution

© 2020 Federation of European Biochemical Societies Staphylococcus aureus is a bacterial pathogen and one of the leading causes of healthcare-acquired infections in the world. The growing antibiotic resistance of S. aureus obliges us to search for new drugs and treatments. As the majority of antibiotics target the ribosome, knowledge of its detailed structure is crucial for drug development. Here, we report the cryo-EM reconstruction at 3.2 Å resolution of the S. aureus ribosome with P-site tRNA, messenger RNA, and 10 RNA modification sites previously not assigned or visualized. The resulting model is the most precise and complete high-resolution structure to date of the S. aureus 70S ribosome with functional ligands

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

© 2020, The Author(s). For 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

A preliminary X-ray diffraction study of the laccase from Coriolus zonatus in the native state

The copper-containing enzyme laccase is involved, owing to its oxidase activity, in the biodegradation of lignins-one of the most important bioconversion processes. On the basis of the X-ray diffraction data for the laccase from Coriolus zonatus, the spatial structure of this enzyme is determined with a resolution of 3.2 angstrom. R and R-free are 0.2347 and 0.2976, respectively, and the rms deviations of the bond lengths and the bond angles are 0.009 and 1.547 angstrom, respectively. The three-domain structure of the laccase from Coriolus zonatus is confirmed, where each domain is represented by a protein from the cupredoxin family. The spatial organization of the active center of the protein is established. The mononuclear center contains a copper ion Cu(1) with the atoms of S_Cys453, ND1_His395, and ND1_His458 ligands. The trinuclear center is formed by copper ions Cu(2), Cu(3), and Cu(4), surrounded by ligands of eight nitrogen atoms of the histidines of the first and third domains of the protein His66, His109, His454, His111, His400, His452, His64, and His398. The Cu(1) ion is located at distances of 11.84 and 13.22 angstrom from the Cu(2) and Cu(3) ions, respectively. The distance between the Cu(2) and Cu(3) ions is 5.14 angstrom and the Cu(4)-Cu(2) and Cu(4)-Cu(3) distances are 4.75 and 4.41 angstrom, respectively.</p