One-step synthesis of vanadium-doped anatase mesocrystals for Li-ion battery anodes.

Here we report a successful one-step synthesis of vanadium-doped anatase mesocrystals by reactive annealing of NH4TiOF3/PEG2000 mesocrystal precursors with NH4VO3. The formation solid solution Ti1-xVxO2with vanadium content up tox = 25 at% inheriting the structure of mesocrystals is observed for the first time. The doping mechanism via vapor phase transport of vanadium is proposed. The Ti1-xVxO2mesocrystals exhibit improved specific capacity of 175 mAh g-1(compared to 150 mAh g-1for pure anatase phase) and decreased potential gap between charge and discharge processes.

[2D [1H,13C] NMR study of carbon fluxes during glucose utilization by Escherichia coli MG1655].

Carbon fluxes through main pathways of glucose utilization in Escherichia coli cells--glycolysis, pentose phosphate pathway (PPP), and Enther-Doudoroff pathway (EDP)--were studied. Their ratios were analyzed in E. coli strains MG1655, MG1655(edd-eda), MG1655(zwf, edd-eda), and MG1655(pgi, edd-eda). It was shown that the carbon flux through glycolysis was the main route of glucose utilization, averaging ca. 80%. Inactivation of EDP did not affect growth parameters. Nevertheless, it altered carbon fluxes through the tricarboxylic acid cycles and energy metabolism in the cell. Inactivation of PPP decreased growth rate to a lesser degree than glycolysis inactivation.

[Residual dipolar couplings and molecular dynamic calculations as a source for refinement of protein spatial structures].

The precision of techniques and factors affecting the interpretation of residual dipolar couplings (RDCs) in analysis of spatial structures of partially aligned proteins are discussed. Experimental RDC values were obtained for pairs of 1H-15N nuclei of the protein barstar partially aligned in a liquid crystalline matrix of bicelles composed of dimiristoylphosphatidylcholine and dihexanoylphosphatidylcholine. The observed couplings agree well with the spatial structures of barstar determined earlier by X-ray and NMR methods. However, the differences between the experimental and calculated RDCs that were calculated on the basis of the known spatial structures of barstar, exceed the experimental errors three- to fourfold. These discrepancies can be explained by differences in the protein structures in solution and in crystal, a limited precision of the X-ray analysis, and the intramolecular mobility of the protein molecule. A comparison of the results of modeling of the molecular dynamics of barstar in solution, crystal structures, and the experimental RDCs showed that the methods of molecular dynamics provide for a reasonable description of the character and amplitudes of internal motions and they should be considered for the correct determination of protein spatial structures from NMR spectroscopic data.

Toxic principle of selva ant venom is a pore-forming protein transformer.

Ectatomin (Ea) is a newly isolated main toxic component of Ectatomma tuberculatum ant venom. Structural and electrophysiological studies were performed with purified Ea. The protein consists of two homologous polypeptide chains (37 and 34 residues) and forms a four alpha-helix bundle in aqueous solution. On insertion into artificial bilayer membranes, two Ea molecules form an ion pore. Our results suggest that the 'inside-out' mechanism of pore formation requires a significant movement of Ea helical parts. The pore formation in the cell membrane might well explain the toxic activity of Ea, not excluding at the same time its intracellular activities.

Solvent magnetization artifacts in high-field NMR studies of macromolecular hydration.

With the use of high magnetic fields and improved quality factor ratings of the probeheads in modern NMR spectrometers, radiation damping becomes more and more important. In addition, the demagnetizing field effect from protonated solvents gains significance with the increase of the magnetic field strength. During a typical NMR pulse sequence the magnetic fields caused by these effects become time-dependent, which makes the system nonlinear and may, for example, measurably influence the precession frequencies of all nuclei in the sample. Since radiation damping can affect signals that are several kilohertz away from the solvent resonance, the amplitude, phase, and frequency of the desired signals can be disturbed so as to give rise to spectral artifacts. In particular when difference methods are used to obtain the final spectrum, the data sets may be severely deteriorated by such artifacts. This paper investigates effects from the demagnetizing field and from radiation damping with a selection of pulse sequences in use for studies of macromolecular hydration, and strategies are described for the detection and elimination of the ensuing artifacts.

[Spatial structure of (1-36)bacterioopsin solubilized in a methanol-chloroform mixture with sodium dodecylsulfate micelles]. / Prostranstvennaia struktura (1-36)bakterioopsina, soliubilizirovannogo v smesi metanol-khloroform i mitsellakh dodetsilsul'fata natriia.

Spatial structures of proteolytic segment A (sA) of bacterioopsin of Halobacterium halobium (residues 1-36) solubilized in the mixture of methanol-chloroform (1:1), 0.1 M LiClO4 or in perdeuteriated sodium dodecyl sulfate (SDS) micelles, were determined by 2D 1H-NMR techniques. Most of the resonances in 1H-NMR spectra of fragment A were assigned using DQF-COSY, TOCSY and NOESY spectra. Deuterium exchange rates for amide protons were measured in series of NOESY spectra. 324 and 400 NOESY cross-peak volumes were measured in NOESY spectra of sA in mixture of organic solvents and SDS micelles, respectively. The sA structure was determined by local structure analysis, distance geometry calculation with program DIANA and systematic search for energetically allowed side chain rotamers consistent with NOESY cross-peak volumes. The structures of sA are similar in both milieus. These structures have the right-handed alpha-helical region from Pro-8 to Met-32 with root mean square deviation (RMSD) of 0.25 A between back bone heavy atoms and fit well with Pro-8 to Met-32 alpha-helical region in electron cryo-microscopy (ECM) model of bacteriorhodopsin [4]. The C-terminal region Gly-33-Asp-36 is disordered in both milieus, while N-terminal region Ala-2-Gly-6 in organic solvents has a fixed structure (RMSD of 0.25 A) stabilized by the Thr-5 NH...O=C Gln-3 and Ile-4 NH...O = C Ala-2 hydrogen bonds. This region of sA in SDS micelles has disordered structure with RMSD of 1.44 A for back bone heavy atoms. Torsion angles chi 1 of sA were unequivocally determined for 72% of side chains in the alpha-helical region and are identical in both milieus.

[Principles of quantitative analysis of two-dimensional spectra of nuclear Overhauser effect in evaluation of protein and peptide conformation]. / Printsipy kolichestvennogo analiza dvumernykh spektrov iadernogo éffekta Overhauzera pri postroenii prostranstvennoi struktury peptidov i belkov.

To elucidate potentialities of two-dimensional homonuclear Overhauser effect (NOESY) spectra of peptides and proteins for their spatial structure determination, impact of experimental parameters and intrinsic properties of the investigated molecule on proton cross-peak volumes in NOESY spectra was analysed. Recommendations which could increase accuracy of cross-peak volume measurements were suggested. Influence of intrinsic properties of a molecule (spin-lattice relaxation times T1, correlation time tau C and surrounding protons) on the volume of cross-peak for particular protons was analyzed using a complete relaxation matrix of the (formula; see text) helix of gramicidin A. Nonselective relaxation time T1 of the protons was found to affect only slightly the results of cross-peak volumes computer simulation, whereas correlation time tau C and surrounding protons seriously influenced cross-peak volumes. Nevertheless, cross-peak volumes between NH, C alpha H and C beta H protons of a dipeptide fragment of the entire molecule could be accurately simulated using the relaxation matrix of the individual dipeptide. Thus local conformations (torsion angles phi, psi and chi 1) of amino acid residues could be deduced independently of one another and prior to the complete analysis of a molecular structure. The result can be obtained even in the presence of spin-diffusion at mixing times providing maximal volumes of cross-peaks in NOESY spectra.

[Determination of local conformation of proteins from 1H-NMR spectroscopy data]. / Metodika opredeleniia lokal'noi konformatsii belkov po dannym spektroskopii 1H-IaMR.

A method is proposed to determine conformations of amino acid residues of the protein and effective correlation time tau c from cross-peak intensities in two-dimensional nuclear Overhauser enhancement (NOESY) spectra. The method consists in fitting complete relaxation matrix of dipeptide unit protons to experimental cross-peak intensities by varying phi, psi, chi torsional angles and tau c. To verify the method, NOESY spectra of basic pancreatic trypsin inhibitor (BPTI) were theoretically generated at mixing times tau m = 25-300 ms and tau c = 4 ns and used for local structure determination. The method works well with optimum for measurement of NOE intensities tau m 100-200 ms. As a result, the backbone phi, psi torsion angles were unambiguously determined at tau m = 100 ms for all but Gly residues of BPTI, and chi 1 angles were determined for the majority of side chains. The obtained dipeptide unit conformations are very close to the BPTI crystallographic structure: root mean square deviation (RMSD) of interproton distances within dipeptide units, on the average, is 0.08 A (maximal deviation 0.44 A), and RMSD of phi and psi angles are 18 and 9 degrees, respectively (maximal deviations are 44 and 22 degrees).

[Structure-activity study of the basic toxic component of venom from the ant Ectatomma tuberculatum]. / Strukturno-funktsional'noe issledovanie osnovnogo toksicheskogo komponenta iada murav'ia Estatomma tuberculatum.

A toxic principle of the Ectatomma tuberculatum ant venom called ectatomin was isolated. Ectatomin is a protein with molecular weight 7928 Da. Its complete amino acid sequence and spatial structure in aqueous solution were determined by protein chemistry methods and NMR spectroscopy techniques. Ectatomin contains two highly homologous polypeptide chains linked to each other by a disulfide bond. The chains consist of 37 and 34 amino acid residues with an internal disulfide bridge in each. In aqueous solution the molecule forms a bundle of four amphipathic alpha-helices. This toxin in a concentration of 0.05-0.01 mM forms potential dependent nonselective cation channels both in cell and artificial membranes. The channel is dimeric and the mechanism of its formation can be explained in terms of the spatial structure established.

[Isolation, biological properties, and spatial structure of an antibiotic loloatin A]. / Vydelenie, biologicheskie svoistva i prostranstvennaia struktura antibiotika loloatina A.

Peptide antibiotic with cyanolytic activity was isolated from the IGM52 strain of the Brevibacillus laterosporus Gram-positive spore-forming bacteria. By 1H NMR spectroscopy, this antibiotic was identified as loloatin A, a cyclic decapeptide cyclo(-Asn-Asp-Tyr-Val-Orn-Leu-DTyr-Pro-Phe-DPhe-). The spatial structure of loloatin A in solution was determined. The English version of the paper: Russian Journal of Bioorganic Chemistry, 2002, vol. 28, no. 4; see also http://www.maik.ru.

Sequence-specific resonance assignment and secondary structure of (1-71) bacterioopsin.

The conformation of chymotryptic fragment C2 of bacteriohodopsin (residues 1-71) was studied by 2D 1H NMR. The fragment was solubilized in a mixture of chloroform/methanol (1:1), 0.1 M LiClO4. Most of the resonances in 1H NMR spectra of fragment C2 were assigned using phase-sensitive DQF-COSY, TOCSY, and NOESY techniques. To simplify the assignment procedure for overlapping regions of NMR spectra, an analog of fragment C2 with leucines deuterated in beta-positions was used. Deuterium exchange rates for amide protons were measured in a series of TOCSY spectra. Two right-handed alpha-helical regions Pro8-Lys30 and Lys41-Leu62 were identified on the basis of NOE connectivities and deuterium exchange rates. The N-terminal part of the fragment (Ala2-Gly6) adopts the helical conformation stabilized by 3 hydrogen bonds.

Three-dimensional structure of ectatomin from Ectatomma tuberculatum ant venom.

Two-dimensional 1H NMR techniques were used to determine the spatial structure of ectatomin, a toxin from the venom of the ant Ectatomma tuberculatum. Nearly complete proton resonance assignments for two chains of ectatomin (37 and 34 amino acid residues, respectively) were obtained using 2D TOCSY, DQF-COSY and NOESY experiments. The cross-peak volumes in NOESY spectra were used to define the local structure of the protein and generate accurate proton-proton distance constraints employing the MARDIGRAS program. Disulfide bonds were located by analyzing the global fold of ectatomin, calculated with the distance geometry program DIANA. These data, combined with data on the rate of exchange of amide protons with deuterium, were used to obtain a final set of 20 structures by DIANA. These structures were refined by unrestrained energy minimization using the CHARMm program. The resulting rms deviations over 20 structures (excluding the mobile N- and c-termini of each chain) are 0.75 A for backbone heavy atoms, and 1.25 A for all heavy atoms. The conformations of the two chains are similar. Each chain consists of two alpha-helices and a hinge region of four residues; this forms a hairpin structure which is stabilized by disulfide bridges. The hinge regions of the two chains are connected together by a third disulfide bridge. Thus, ectatomin forms a four-alpha-helical bundle structure.

The secondary structure of phospholamban: a two-dimensional NMR study.

Phospholamban (PLN) is an intrinsic membrane protein of 52 amino acids which regulates the Ca2+ pump of the sarcoplasmic reticulum of heart, slow-twitch and smooth muscle (SR): it is normally assumed to exist in the membrane as a homopentamer. A monomeric analogue of phospholamban PLN(C41F), in which Cys41 was replaced by a Phe, was synthesized and its conformation studied by 1H NMR spectroscopy in a 1:1 mixture of chloroform/methanol. Most of the resonances in the 1H NMR spectra were assigned. The work has shown that the C-terminal hydrophobic portion forms a very stable alpha-helix. The hydrophilic N-terminal part adopts an alpha-helix configuration which is much less stable except for the stretch containing the phosphorylation sites.

Two distinct structures of alpha-conotoxin GI in aqueous solution.

The detailed analysis of conformational space of alpha-conotoxin GI in aqueous solution has been performed on the basis of two-dimensional NMR spectroscopy data using multiconformational approach. As the result, two topologically distinct interconvertible sets of GI conformations (populations of 78% and 22%) have been found. A common feature of the two sets is the Asn4-Cys7 beta-turn. The Gly8 to Tyrll region has a structure of right-handed helical turn in the major set and two sequential bends in the minor one. N-terminus and C-terminus also have different orientations, anti-parallel in the major conformational set and parallel in the minor one. An average pairwise rmsd for backbone heavy atoms is 0.56 A in the major set, 0.23 A in the minor, and 1.85 A between the structures of the two sets. The X-ray structure of GI [Guddat, L. W., Martin, J. A., Shan, L., Edmundson, A. B. & Gray, W. R. (1996) Biochemistry 35, 11329 - 11335] has the same folding pattern as the major NMR set, the average backbone rmsd between the two structures being 0.77 A.