The lipopeptaibol trichogin GA IV is a 10 amino acid-long residue and
α-aminoisobutyric acid-rich antibiotic peptide of fungal origin. TOAC (2,2,6,6-tetramethylpiperidine-1-oxyl-4-amino-4-carboxylic ...acid) spin-labeled analogs of this membrane active peptide were investigated in hydrated bilayers of dipalmitoylphosphatidylcholine by electron spin echo envelope modulation (ESEEM) spectroscopy and pulsed electron-electron double resonance (PELDOR). Since, the ESEEM of the spin label appears to be strongly dependent on the presence of water molecules penetrated into the membrane, this phenomenon was used to study the location of this peptide in the membrane. This was achieved by comparing the ESEEM spectra for peptides labeled at different positions along the amino acid sequence with spectra known for lipids with spin labels at different positions along the hydrocarbon chain. To increase the ESEEM amplitude and to distinguish the hydrogen nuclei of water from lipid protons, membranes were hydrated with deuterated water. The PELDOR spectroscopy technique was chosen to study peptide aggregation and to determine the mutual distance distribution of the spin-labeled peptides in the membrane. The location of the peptide in the membrane and its aggregation state were found to be dependent on the peptide concentration. At a low peptide/lipid molar ratio (less than 1:100) the nonaggregated peptide chain of the trichogin molecules lie parallel to the membrane surface, with TOAC at the 4th residue located near the 9th–11th carbon positions of the
sn-2 lipid chain. Increasing this ratio up to 1:20 leads to a change in peptide orientation, with the N-terminus of the peptide buried deeper into membrane. Under these conditions peptide aggregates are formed with a mean aggregate number of about
N
=
2. The aggregates are further characterized by a broad range of intermolecular distances (1.5–4
nm) between the labels at the N-terminal residues. The major population exhibits a distance of ∼2.5
nm, which is of the same order as the length of the helical peptide. We suggest that the constituting monomers of the dimer are antiparallel oriented.
The method of pulsed electron-electron double resonance (PELDOR) is exploited to study intra- and intermolecular dipole-dipole interactions between the spin labels of trichogin GA IV analogues. This ...lipopeptaibol antibiotic was studied in multilamellar membranes of dipalmitoylphosphatidylcholine frozen to 77 K. For mono-labelled trichogin analogues, the molecules are shown not to form aggregates in the lipid membranes studied. For the double-labelled trichogin analogues, a function of the distance distribution between the spin labels has been obtained. We determined that the distribution function has two main maxima located at distances of 1.25 nm and 1.75 nm. The value of 1.25 nm is close to the distance between labels of a alpha-helical structure. On the other hand, a distance of 1.75 nm corresponds to a mixed 3D-structure in which a 3(10)-helix is combined with a more elongated conformation.
The new technique of pulsed electron−electron double resonance in electron spin−echo (PELDOR) in combination with the CW-ESR method has been used to investigate the secondary structure of a double ...spin-labeled peptide (the TOAC-1,8-analogue of the peptaibol antibiotic trichogin GA IV) that is hidden into a tetrameric supramolecular assembly of unlabeled peptide molecules. The magnetic dipole−dipole relaxation of spin labels has been experimentally studied in glassy solutions of the double-labeled peptide frozen to 77 K in a mixture of chloroform−toluene with an excess of unlabeled peptide. The PELDOR signal oscillations have been observed at high degrees of dilution with unlabeled peptide. The intramolecular distance between the spin labels of the peptide molecule in the aggregate has been determined from the oscillation frequency to be 15.7 Å which is close to the value of ≅14 Å calculated for a 310-helical structure. Estimation of the fraction of this ordered secondary structure shows that about 19% of the peptide molecules in aggregates are folded in the 310-helical conformation. The present experimental results are consistent with our molecular model presented in J. Am. Chem. Soc. 2000, 122, 3843−3848, wherein four amphiphilic 310-helical peptide molecules form a vesicular system with the polar amino acid side chains pointing to the interior, and the apolar side chains, to the exterior of the cluster. The experimental data were compared with the results obtained with other techniques.
The impact of pumping pulse duration on four-pulse pulsed electron–electron double resonance (PELDOR) data was experimentally studied. For biradicals with known distances between two spin labels, it ...is shown that refocused echo amplitude decreases with increasing the pumping pulse duration and decreasing the distance between spin labels. The effect becomes substantial when the pumping pulse duration is comparable or exceeds the inverse value of the dipole–dipole interaction between spin labels. This effect is essential for determination of distance distribution between labels in double-labeled molecules and for determination of the number of labels in clusters of spin-labeled molecules. PELDOR signal distortion was observed when the pumping pulse position in the time scale coincided with those of the detecting pulses. An approach of signal correction to eliminate this distortion is proposed.
The papers related to the theoretical background and experimental investigations by pulsed electron double resonance (PELDOR) are reviewed. The main aim of this pulsed ESR application is to study the ...dipole-dipole spin interaction. In PELDOR the ESR spectrum is excited by two ESE pulses at frequencyωa and additional pumping pulse atωb. Decay functionV(T) of the ESE signal, when the time intervalT between the first ESE pulse and pumping pulse is varied, contains the information on dipole-dipole couplings in the spin system. The kinetics ofV(T) decay strongly depends upon distance, mutual orientation inside interacting spin pairs and space distribution of radicals throughout the sample. The distances between spins which were measured or estimated using PELDOR in the papers reviewed are in the range of 15 ÷ 130 Å. This pulsed ESR technique turns now to be a powerful supplement to conventional ESE in studying the free radicals space distribution..
Reported here are transverse single-spin asymmetries (AN) in the production of charged hadrons as a function of transverse momentum (pT) and Feynman-x (xF) in polarized p↑ + p, p↑ + Al, and p↑ + Au ...collisions at $\sqrt{^SNN}$ = 200 GeV. The measurements have been performed at forward and backward rapidity (1.4 < |η| < 2.4) over the range of 1.5 GeV /c < pT < 7.0 GeV /c and 0.04 < |xF| < 0.2. A nonzero asymmetry is observed for positively charged hadrons at forward rapidity (xF > 0) in p↑ + p collisions, whereas the p↑ + Al and p↑ + Au results show smaller asymmetries. This finding provides new opportunities to investigate the origin of transverse single-spin asymmetries and a tool to study nuclear effects in p + A collisions.
Polarized proton-proton collisions provide leading-order access to gluons, presenting an opportunity to constrain gluon spin-momentum correlations within transversely polarized protons and enhance ...our understanding of the three-dimensional structure of the proton. Midrapidity open-heavy-flavor production at $\sqrt{s}$ = 200 GeV is dominated by gluon-gluon fusion, providing heightened sensitivity to gluon dynamics relative to other production channels. Transverse single-spin asymmetries of positrons and electrons from heavy-flavor hadron decays are measured at midrapidity using the PHENIX detector at the Relativistic Heavy Ion Collider. These charge-separated measurements are sensitive to gluon correlators that can in principle be related to gluon orbital angular momentum via model calculations. Explicit constraints on gluon correlators are extracted for two separate models, one of which had not been constrained previously.
Pulsed electron−electron double-resonance (PELDOR) and CW-ESR spectroscopies were used to study the dipole−dipole interaction of spin labels in frozen glassy solutions of mono- and double-labeled ...analogues of the 22-residue, the head-to-tail covalent dimer of the peptaibol antibiotic trichogin GA IV. The TOAC-1 and TOAC-1,19 dimers were studied in methanol and in a chloroform−toluene mixture. It was shown these dimer molecules do not form aggregates in methanol. However, in chloroform−toluene, the PELDOR signal of the mono-labeled dimer shows oscillations, due to the dipole−dipole interaction of the nitroxide spin labels. From the signal decay, the number of molecules per aggregate was estimated to be ∼2−3, depending on the concentration used. The contributions of inter- and intra-aggregate interactions of spin labels to the PELDOR signal decay were separated. The distance distribution functions of the intra-aggregate interactions range from 3.0 to 4.5 nm. The maxima are observed at 3.4 nm. From the PELDOR data, we obtained the functions of distance distributions of labels for the monomeric double-labeled peptide in methanol as well as for the same peptide isolated within aggregates of nonlabeled peptide molecules in chloroform−toluene. In the latter case, the distribution function is the most narrow with a maximum at a distance between the nitroxide spin labels of 2.8 nm, which is in agreeement with the theoretical distance between labels at corresponding residue positions of an α-helical structure.
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