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Application of dehydroalanine as a building block for the synthesis of selenocysteine-containing peptides
No full textSelenocysteine (Sec), the 21(st) proteinogenic amino acid, is inserted co-translationally into number of natural proteins. It is coded by a dual function stop codon UGA (opal). It is a redox active amino acid found at the active sites of several enzymes that are involved in oxidation-reduction reactions. These enzymes include the three major mammalian selenoproteins glutathione peroxidase (GPx), thioredoxin reductase (TrxR), and iodothyronine deiodinase (Dio). Although Sec is structurally similar to its sulfur analogue cysteine (Cys), the lower pK(a) of the selenol group in Sec as compared to that of Cys and the interesting redox properties of the selenium atom in peptides and proteins play crucial roles in redox catalysis. However, the chemical synthesis of Sec-containing peptides has been a difficult task. In this paper, we report on a new method for the synthesis of Sec and Sec-containing peptides using dehydroalanine (Dha) as a building block
Study of EIT resonances in an anti-relaxation coated Rb vapor cell
No full textWe study the sign of resonances obtained in electromagnetically induced transparency (EIT). Resonances of both kinds-bright (corresponding to enhanced absorption) and dark (corresponding to reduced absorption)-are obtained when the frequency of a probe beam is scanned. The experimental results, presented earlier, use magnetic sublevels of a hyperfine transition in the D-1 line of Rb-87 along with a magnetic field of 27 G. The atoms are contained in a vapor cell at room temperature, and with anti-relaxation coating on the walls. A quantitative theoretical model, which reproduces the experimental results quite well, is presented for the first time. The model solves the density matrix of the sublevels involved, and uses two regions-one with both the light and magnetic field, and the second without light and just a magnetic field. This ability to have both bright and dark resonances promises applications in sub- and super-luminal propagation of light. (C) 2018 Elsevier B.V. All rights reserved
Enteropathogens: Tuning Their Gene Expression for Hassle-Free Survival
No full textEnteropathogenic bacteria have been the cause of the majority of foodborne illnesses. Much of the research has been focused on elucidating the mechanisms by which these pathogens evade the host immune system. One of the ways in which they achieve the successful establishment of a niche in the gut microenvironment and survive is by a chain of elegantly regulated gene expression patterns. Studies have shown that this process is very elaborate and is also regulated by several factors. Pathogens like, enteropathogenic Escherichia coli (EPEC), Salmonella Typhimurium, Shigella flexneri, Yersinia sp. have been seen to employ various regulated gene expression strategies. These include toxin-antitoxin systems, quorum sensing systems, expression controlled by nucleoid-associated proteins (NAPs), several regulons and operons specific to these pathogens. In the following review, we have tried to discuss the common gene regulatory systems of enteropathogenic bacteria as well as pathogen-specific regulatory mechanisms
Mismatch in receiver responses to multimodal signals in a diurnal gecko
No full textMultimodal signals are used by many animals for intraspecific communication and can provide information about sex identity as well as quality of the signaller. In diurnal geckos of the genus Cnemaspis, chromatic colour patches in males evolved after chemical secretions, providing us with an opportunity to examine the utility of evolving multimodality. We quantified signal components and receiver responses in Cnemaspis mysoriensis to determine the relative importance of chemical and visual traits for intraspecific communication. Digital imagery and spectrophotometry of lizards revealed the presence of two distinct male morphs (yellow-gular and white-gular) and one female form (white-gular). All males, but no females, had yellow eye rims. Characterization of chemical secretions from the ventral precloacal and femoral glands of all lizard forms revealed no differences between male morphs. However, all males differed from females in a few key compounds. We then exposed lizards to only chemical stimuli, only visual stimuli, or both chemical and visual stimuli of conspecific males and females. We found that females were responsive to the chemical stimuli alone as well as the multimodal stimuli of males, whereas males were only responsive to the multimodal stimuli of other males. Neither chemical or visual components of females elicited a response from conspecifics. Thus, while the chemical secretions of males are sufficient for females to elicit a response, multimodal stimuli are necessary for males to respond. Based on variation in signalling traits and receiver responses, we conclude that: (1) chemical secretions signal both sex identity and male quality; (2) eye rim colour encodes information about sex identity; and (3) gular colour in males is probably not a redundant trait, providing some information to males, but not females. We conclude that the secondary evolution of visual signals in C. mysoriensis therefore enhances male-male social interactions and not communication in general. (C) 2018 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved
Water Remediation Aided by a Graphene-Oxide-Anchored Metal Organic Framework through Pore- and Charge-Based Sieving of Ions
No full textHerein, a unique reversible addition-fragmentation chain transfer (RAFT)-synthesized antibacterial copolymer was designed to target key requirements such as stringent and quick response toward bacteria and quick reversible response toward fouling using a multilayered assembly. In order to render the membrane assembly selective toward ions, a unique phosphonium-conjugated graphene oxide (P(+)GO)-anchored copper- and trimesic-acid-based metal organic framework (CuMOF) was sandwiched between the RAFT-synthesized polymer and a commercial reverse osmosis (RO) support. The sandwich architecture exhibited excellent antibacterial properties for both Gram-positive and Gram-negative bacterial cells. The membranes also retained an unimpeded flow of water even after longer continuous runs. The engineered active layer was excellent in rendering reversible antifouling against bovine serum albumin with 98.8% flux retention. The nanoexclusions/channels offered by the P(+)GO-anchored CuMOF, sandwiched as an interlayer, though reduced the flux as compared to the support RO but manifested in an exemplary 99.9% salt removal for a formulation composed of monovalent and divalent ions through synergistic charge- and pore-based sieving. This multilayered assembly is bactericidal, is resistant to scaling unlike the base RO support, and shows excellent ion-sieving characteristics that makes it a potential candidate in water remediation
Structural insights into the activation of metabotropic glutamate receptors
No full textMetabotropic glutamate receptors are family C G-protein-coupled receptors. They form obligate dimers and possess extracellular ligand-binding Venus flytrap domains, which are linked by cysteine-rich domains to their 7-transmembrane domains. Spectroscopic studies show that signalling is a dynamic process, in which large-scale conformational changes underlie the transmission of signals from the extracellular Venus flytraps to the G protein-coupling domains-the 7-transmembrane domains-in the membrane. Here, using a combination of X-ray crystallography, cryo-electron microscopy and signalling studies, we present a structural framework for the activation mechanism of metabotropic glutamate receptor subtype 5. Our results show that agonist binding at the Venus flytraps leads to a compaction of the intersubunit dimer interface, thereby bringing the cysteine-rich domains into close proximity. Interactions between the cysteine-rich domains and the second extracellular loops of the receptor enable the rigid-body repositioning of the 7-transmembrane domains, which come into contact with each other to initiate signalling
A Unidirectional Single-Stage Three-Phase Soft-Switched Isolated DC-AC Converter
No full textThis paper presents a novel single-stage soft-switched high-frequency-link three-phase dc-ac converter topology. The topology supports unidirectional dc to ac power flow and is targeted for applications like grid integration of photovoltaic sources, fuel cell, etc. The high frequency magnetic isolation results in reduction of system volume, weight, and cost. Sine-wave pulsewidth modulation is implemented in dc-side converter. Though high-frequency switched, dc-side converter is soft switched for most part of the line cycle. The ac-side converter active switches are line frequency switched incurring negligible switching loss. The line frequency switching of ac-side converter facilitates use of high voltage blocking inherently slow semiconductor devices to generate high voltage ac output. In addition, a cascaded multilevel structure is presented in this paper for direct medium-voltage ac grid integration. A detailed circuit analysis considering nonidealities like transformer leakage and switch capacitances, is presented in this paper. A 6-kW three-phase laboratory prototype is built. The presented simulation and experimental results verify the operation of the proposed topologies
Live cell super resolution imaging by radial fluctuations using fluorogen binding tags
No full textFluorescence-Activating and absorption-Shifting Tag (FAST) is a novel genetically encoded optical highlighter probe. Since the fluorescence of FAST originates from the stochastic and reversible diffusive association of a fluorogenic ligand, we investigate the application of FAST using Super-Resolution Radial Fluctuations (SRRF) to achieve routine imaging below the diffraction limit in a widefield epifluorescence microscope. We show that intensity fluctuation analysis like SRRF allows the imaging of FAST-tagged proteins with sub - 100 nm resolution in live cells. FAST co-labeled with conventional fluorophores enables real time multicolour 2D and 3D super-resolution imaging, indicating that FAST can be used for the observation of sub-diffraction limited structures in both living and fixed samples
Unfolding Dynamics of Ubiquitin from Constant Force MD Simulation: Entropy-Enthalpy Interplay Shapes the Free-Energy Landscape
No full textForce probe methods are routinely used to study conformational transitions of biomolecules at single-molecule level. In contrast to simple kinetics, some proteins show complex response to mechanical perturbations that is manifested in terms of unusual force-dependent kinetics. Here, we study, via fully atomistic molecular dynamics simulations, constant force-induced unfolding of ubiquitin protein. Our simulations reveal a crossover at an intermediate force (about 400 pN) in the unfolding rate versus force curve. We find by calculation of multidimensional free-energy landscape (FEL) of the protein that the complex unfolding kinetics is intimately related to the force-dependent modifications in the FEL. Pearson correlation coefficient analysis allowed us to identify two appropriate order parameters describing the unfolding transition. The crossover in the rate can be explained in terms of an interplay between entropy and enthalpy with relative importance changing from low force to high force. We rationalize the results by using multidimensional transition-state theory
Fragmentation of J/psi in jets in pp collisions at root s=5.02 TeV Batoul Diab for the CMS collaboration
No full textThe fragmentation of jets containing a J/psi meson is studied in root s = 5.02 TeV pp data using an integrated luminosity of L = 27.39 pb(-1). The fraction of the jet transverse momentum p(Tjet) carried by the J/psi is measured for prompt J/psi and J/psi coming from b hadron decays, named nonprompt. Whereas the fragmentation function of nonprompt J/psi is well-modeled by simulations using a Monte Carlo generator, the prompt J/psi are found to be accompanied by a larger level of jet activity. The fraction of J/psi mesons that are produced inside a jet is also reported, and found to be larger in data than in simulation, for both prompt and nonprompt J/psi