1,720,960 research outputs found
Epr Spectroscopy of Adsorbed Spin-Labeled Peptides: Immobilization of Trichogin on the Titanium Oxide
No full textThe TOAC-spin-labeled peptide Trichogin GA IV adsorbed on the TiO2 surface is studied. It is shown that the continuous wave (CW) electron paramagnetic resonance (EPR) spectrum does not depend on temperature in a wide range of 77-300 K. A pulsed EPR method of electron spin echo (ESE) utilizing a two-pulse sequence (/2--) is used to study temperature dependence of the phase relaxation time, T-F. The T-F values are found to change from 750 ns to 100 ns in the interval of 77-300 K. The pulsed electronelectron double resonance (PELDOR) measurements utilizing the pulse sequence((/2)(A),-T-(B),-(-T)-(A)) show that the space distribution of spin labels on the surface remains uniform irrespective of the temperature, and provide the fractal dimension of the surface of 2.7 +/- 0.1. The obtained results testify that EPR pulse experiments can be used to study adsorbed spin-labeled molecules at room temperatures, i.e. not only at cryogenic temperatures
Tylopeptin B peptide antibiotic in lipid membranes at low concentrations: Self-assembling, mutual repulsion and localization
No full textThe medium-length peptide Tylopeptin B possesses activity against Gram-positive bacteria. It binds to bacterial membranes altering their mechanical properties and increasing their permeability. This action is commonly related with peptide self-assembling, resulting in the formation of membrane channels. Here, pulsed double electron-electron resonance (DEER) data for spin-labeled Tylopeptin B in palmitoyl-oleoyl-glycero-phosphocholine (POPC) model membrane reveal that peptide self-assembling starts at concentration as low as 0.1 mol%; above 0.2 mol% it attains a saturation-like dependence with a mean number of peptides in the cluster = 3.3. Using the electron spin echo envelope modulation (ESEEM) technique, Tylopeptin B molecules are found to possess a planar orientation in the membrane. In the peptide concentration range between 0.1 and 0.2 mol%, DEER data show that the peptide clusters have tendency of mutual repulsion, with a circle of inaccessibility of radius around 20 nm. It may be proposed that within this radius the peptides destabilize the membrane, providing so the peptide antimicrobial activity. Exploiting spin-labeled stearic acids as a model for free fatty acids (FFA), we found that at concentrations of 0.1–0.2 mol% the peptide promotes formation of lipid-mediated FFA clusters; further increase in peptide concentration results in dissipation of these clusters
DEER/PELDOR Study of the Effect of Extremely Low Concentrations of the Antimicrobial Peptide Chalciporin A on the Membrane Lipid Organization
No full textAntimicrobial peptides (AMPs) are promising therapeutic agents against drug-resistant bacteria. Many AMPs can directly interact with bacterial membranes, disturbing their integrity and/or functionality. Chalciporin A is a naturally occurring 14-mer AMP, belonging to the class of peptaibiotic. Spin-label electron paramagnetic resonance in its pulsed versions is a suitable tool to study intermolecular interactions in biological media. Here, we applied double electron-electron resonance (DEER, also known as PELDOR) and electron spin echo envelope modulation, to study model membranes of palmitoyl-oleoyl-glycero-phosphocholine in the presence of chalciporin A. The spin-labeled molecules were either chalciporin A or doxyl-spin-labeled stearic acids (DSAs). We observed that chalciporin A influences DSA clustering, disturbing the formation of the alternative sub-clusters in two opposing leaflets that was recently found in peptide-free membranes (Smorygina et al. in Langmuir 37:13909-13916, 2021). The intriguing point of this influence is that it takes place for peptide concentrations as small as 0.01 mol% (1/10,000 peptide-to-lipid ratio). The possible reasons for this membrane perturbation at extremely low concentrations are discussed
A Peptide-Based Trap for Metal Ions Studied by Electron Paramagnetic Resonance
Get PDFPeptide-based materials provide a versatile platform for sensing and ion sequestration since peptides are endowed with stimuli-responsive properties. The mechanism of molecular sensing is often based on peptide structural changes (or switching), caused by the binding of the target molecule. One scope of sensing applications is the selection of a specific analyte, which may be achieved by adjusting the structure of the peptide binding site. Therefore, exact knowledge of peptide properties and 3D-structure in the ‘switched’ state is desirable for tuning the detection and for further molecular construction. Hence, here we demonstrate the performance of Electron Paramagnetic Resonance (EPR) spectroscopy in the identification of metal ion binding by the antimicrobial peptide trichogin GA IV. Na(I), Ca(II), and Cu(II) ions were probed as analytes to evaluate the impact of coordination number, ionic radii, and charge. Conclusions drawn by EPR are in line with literature data, where other spectroscopic techniques were exploited to study peptide-ion interactions for trichogin GA IV, and the structural switch from an extended helix to a hairpin structure, wrapped around the metal ion upon binding of divalent cations was proposed
Is Cys(MTSL) the Best α-Amino Acid Residue to Electron Spin Labeling of Synthetically Accessible Peptide Molecules with Nitroxides?
Get PDFElectron paramagnetic resonance spectroscopy, particularly its pulse technique double electron–electron resonance (DEER) (also termed PELDOR), is rapidly becoming an extremely useful tool for the experimental determination of side chain-to-side chain distances between free radicals in molecules fundamental for life, such as polypeptides. Among appropriate probes, the most popular are undoubtedly nitroxide electron spin labels. In this context, suitable biosynthetically derived, helical regions of proteins, along with synthetic peptides with amphiphilic properties and antibacterial activities, are the most extensively investigated compounds. A strict requirement for a precise distance measurement has been identified in a minimal dynamic flexibility of the two nitroxide-bearing α-amino acid side chains. To this end, in this study, we have experimentally compared in detail the side-chain mobility properties of the two currently most widely utilized residues, namely, Cys(MTSL) and 2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic acid (TOAC). In particular, two double-labeled, chemically synthesized 20-mer peptide molecules have been adopted as appropriate templates for our investigation on the determination of the model intramolecular separations. These double-Cys(MTSL) and double-TOAC compounds are both analogues of the almost completely rigid backbone peptide ruler which we have envisaged and 3D structurally analyzed as our original, unlabeled compound. Here, we have clearly found that the TOAC side-chain labels are largely more 3D structurally restricted than the MTSL labels. From this result, we conclude that the TOAC residue offers more precise information than the Cys(MTSL) residue on the side chain-to-side chain distance distribution in synthetically accessible peptide molecules
Peptides on the Surface: Spin-Label EPR and PELDOR Study of Adsorption of the Antimicrobial Peptides Trichogin GA IV and Ampullosporin A on the Silica Nanoparticles
No full textThe properties of antimicrobial peptides adsorbed on inorganic or
organic surfaces are of interest for their potential applications in
intracellular drug delivery. In this work, continuous-wave (CW) electron
paramagnetic resonance (EPR) and pulsed electron-electron double
resonance (PELDOR) techniques were applied to study adsorption of the
short-sequence trichogin GA IV and the medium-length sequence
ampullosporin A antimicrobial peptides on the monodisperse colloidal
silica nanospheres of 20 nm diameter. The results obtained by CW EPR
support the view that the adsorbed peptides form close-packed clusters.
PELDOR data show that both trichogin and ampullosporin adsorbed on the
silica surface possess a more disordered conformation as compared to
that in solution. For ampullosporin, disordering is much more pronounced
than for trichogin. After desorption, the peptides restored their
conformations; upon adsorption the peptides in some cases may lose
partly their biradical character
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Get PDFWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
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