A. V. Aganov

Antimicrobial peptide protegrin-3 adopt an antiparallel dimer in the presence of DPC micelles: a high-resolution NMR study.

A tendency to dimerize in the presence of lipids was found for the protegrin. The dimer formation by the protegrin-1 (PG-1) is the first step for further oligomeric membrane pore formation. Generally there are two distinct model of PG-1 dimerization in either a parallel or antiparallel β-sheet. But despite the wealth of data available today, protegrin dimer structure and pore formation is still not completely understood. In order to investigate a more detailed dimerization process of PG-1 and if it will be the same for another type of protegrins, in this work we used a high-resolution NMR spectroscopy for structure determination of protegrin-3 (RGGGL-CYCRR-RFCVC-VGR) in the presence of perdeuterated DPC micelles and demonstrate that PG-3 forms an antiparallel NCCN dimer with a possible association of these dimers. This structural study complements previously published solution, solid state and computational studies of PG-1 in various environments and validate the potential of mean force simulations of PG-1 dimers and association of dimers to form octameric or decameric β-barrels.

Structure of pravastatin and its complex with sodium dodecyl sulfate micelles studied by NMR spectroscopy

The aim of this work was to study the mechanisms of interaction between pravastatin and cell membranes using model membranes (sodium dodecyl sulfate micelles) by nuclear magnetic resonance spectroscopy methods. On the basis of the nuclear magnetic resonance experiments, it was established that pravastatin can form intermolecular complexes with sodium dodecyl sulfate micelles by the interaction of its hydrophilic groups with the polar surface of the micelle. Conformational features of pravastatin molecule were also studied. Copyright

Time-resolved EPR study of radicals from 2,2-dimethoxy-2-phenylacetophenone in ethylene glycol after flash photolysis

Abstract The dynamic behaviour of transient free radicals generated by laser pulse photolysis (with λ =351 nm) of 2,2-dimethoxy-2-phenylacetophenone (DMPA) in ethylene glycol solutions have been studied by time-resolved EPR at room temperature. A main result of the study is a suitable evaluation method for radical systems with CIDEP in the case of very close hyperfine lines and hence with a overlap of several signals. The evaluation of single EPR time-profile signals requires in this case to take in account also the influence of the near resonance positions, what successfully has been done. The formation and decay of the two spin polarized radicals, 7,7-dimethoxy-benzyl (R 1 ) and benzoyl radical (R 2 ), has been observed. For R 1 the relaxation time T 2 was determined with a good accuracy and the rate constants k 1 and k 2 were estimated by fitting the time evolution of the EPR signal at resonance and near resonance positions of the field using the Bloch equations and direct Fourier transform analysis. Radicals from DMPA in the high viscous solvent ethylene glycol have been proved to be an excellent model system for this study however the treatment is applicable also for other systems.

Oligomerization of the antimicrobial peptide Protegrin-5 in a membrane-mimicking environment. Structural studies by high-resolution NMR spectroscopy.

Protegrin pore formation is believed to occur in a stepwise fashion that begins with a nonspecific peptide interaction with the negatively charged bacterial cell walls via hydrophobic and positively charged amphipathic surfaces. There are five known nature protegrins (PG1-PG5), and early studies of PG-1 (PDB ID:1PG1) shown that it could form antiparallel dimer in membrane mimicking environment which could be a first step for further oligomeric membrane pore formation. Later, we solved PG-2 (PDB ID:2MUH) and PG-3 (PDB ID:2MZ6) structures in the same environment and for PG-3 observed a strong dαα NOE effects between residues R18 and F12, V14, and V16. These “inconsistent” with monomer structure NOEs appears due to formation of an additional antiparallel β-sheet between two monomers. It was also suggested that there is a possible association of protegrins dimers to form octameric or decameric β-barrels in an oligomer state. In order to investigate a more detailed oligomerization process of protegrins, in the present article we report the monomer (PDB ID: 2NC7) and octamer pore structures of the protegrin-5 (PG-5) in the presence of DPC micelles studied by solution NMR spectroscopy. In contrast to PG-1, PG-2, and PG-3 studies, for PG-5 we observed not only dimer NOEs but also several additional NOEs between side chains, which allows us to calculate an octamer pore structure of PG-5 that was in good agreement with previous AFM and PMF data.

Interaction of different statins with model membranes by NMR data

Hydroxy-methyl-glutaryl-coenzyme A (HMG-CoA) reductase inhibitors or statins reduce the amount of low-density lipoprotein (LDL) cholesterol, which is known as a well-established risk factor for atherosclerosis. Despite the fact that statins have a common pharmacologic target essential to sterol biosynthesis, their efficacy, safety, and potential non-LDL actions vary significantly for different statins. There is a hypothesis that pharmacological features of statins depend on their location in cell membrane, but to the present day there is a lack of information in literature on interactions of statins with the surface of the cell membrane in liquid media. The results of NMR experiments showed that all studied statins form intermolecular complexes with models of cell membranes (dodecylphosphocholine micelles) in water solution. Locations of pravastatin, simvastatin, fluvastatin and cerivastatin on model membranes were established by NOESY NMR data. Distinctions in their positions can explain differences in pharmacological properties of studied compounds.

Dynamic1H,13C,31P NMR spectroscopy of the crown containing N-(thio)phosphoryl(thio)urea

The variable temperature and concentration1H,13C,31P NMR spectroscopy of the N,N′-bis[diisopropoxy(thio)phosphorylamido-(thio)carbonyl]-1,10-diaza-18-crown-6 containing the reaction pentade C(X)NHP(Y) and stereononrigid macrocycle in solutions (CD2CL2, CD3CN, (CD3)2CO as solvent) was studied. The complex chemical exchange is described in terms of tautomeric processes, hindered rotation around C-N bond and macrocycle ring inversion. NMR spectral parameters (chemical shifts and spin-spin coupling constants) of the observed exchange partners as well as thermodynamic parameters of the equilibrium and transition between tautomeric and conformational forms are given.

Cu(II) content in the structures of the peripheral nervous system at their damage

Employing electron paramagnetic resonance with diethyldithiocarbamate as a spin trap it was shown that after the transection of the rat sciatic nerve the Cu(II) content increased in the proximal stump and did not change in the distal stump. No changes of the Cu(II) content in dorsal root ganglia L4-L5 containing sensory neurons with their peripheral processes in the damaged nerve were registered.

Spatial structure of dimeric capsules of tetraurea calix[4]arenes in solutions according to 2-D NMR (NOESY) spectroscopy

Spatial structure of calixarene has been investigated by two-dimensional nuclear magnetic resonance (nuclear Overhauser effect) spectroscopy. Interproton distances for the given compound in solutions of benzene and cyclohexane have been measured and the experimental values have been compared with theoretically predicted ones.

STATINS AND THEIR INTERACTION WITH MODEL CELL MEMBRANES ACCORDING TO THE DATA OF NUCLEAR MAGNETIC RESONANCE SPECTROSCOPY

Aim. To study the location of pravastatin, simvastatin, fluvastatin and cerivastatin in molecular complexes with model cell membranes based on dodecylphosphocholine, and also to calculate the average interatomic distances between the atoms of statins and micelles. Material and methods. Nuclear magnetic resonance (NMR) spectroscopy was chosen as a method of study. NMR spectroscopy of the Overhauser nuclear effect (NOESY) is one of the most effective methods in the study of intermolecular interactions, in particular, in studies of drugs. Information on the spatial structure of the molecular complex, as well as on the fragments of molecules responsible for the effective interaction leading to complex formation, was obtained by NOESY spectroscopy. All NMR experiments were performed on a Bruker Avance II 500 spectrometer with a 5 mm zgradient inverse sensor with the TOPSPIN software. The calculation of the interatomic distances was made with an accuracy of 0.1 A. Results. The location of pravastatin, simvastatin, fluvastatin and cerivastatin in molecular complexes with model cell membranes based on dodecylphosphocholine was determined based on NMR NOESY experiments. The average interatomic distances between the atoms of statins and micelles were also calculated. Pravastatin weakly binds to the polar surface of the model membrane, while simvastatin penetrates into the space between the hydrocarbon chains of the micelle. Fluvastatin interacts mainly with model membranes by penetration of its aromatic fragments into the surface of the micelle. Cerivastatin has a unique arrangement in the model membrane. It is located deep in the hydrophobic nucleus of the micelle close to the terminal methylene group. Conclusion: Even minor differences in the chemical structure of statins lead to different patterns of interaction with model membranes. These differences can explain the characteristics of the pharmacological properties of these substances.

Synthesis of a new quaternary phosphonium salt: NMR study of the conformational structure and dynamics.

A novel phosphonium salt based on pyridoxine was synthesized. Conformational analysis of the compound in solution was performed using dynamic NMR experiments and calculations. The obtained results revealed some differences in the conformational transitions and the energy parameters of the conformational exchange of the studied compound in comparison to previously reported data for other phosphorus‐containing pyridoxine derivatives. It was shown that increasing the substituent at the C‐11 carbon leads to greater differences in the populations of stable states and the corresponding equilibrium energies. Copyright