Probing the interactions of GlcNH2 with boric acid via NMR spectroscopy.

Histotoxic clostridia produce collagenases responsible for extensive tissue destruction in gas gangrene. The C-terminal collagen-binding domain (CBD) of these enzymes is the minimal segment required to bind to collagen fibril. Collagen binding efficiency of CBD is more pronounced in the presence of Ca(2+). We have shown that CBD can be functional to anchor growth factors in local tissue. A (1)H-(15)N HSQC NMR titration study with three different tropocollagen analogues ((POG)(10))(3), ((GPOG)(7)PRG)(3), and (GPRG(POG)(7)C-carbamidomethyl)(3), mapped a saddle-like binding cleft on CBD. NMR titrations with three nitroxide spin-labeled analogues of collagenous peptide, (PROXYL-G(POG)(7)PRG)(3), (PROXYL-G(POG)(7))(3), and (GPRG(POG)(7)C-PROXYL)(3) (where PROXYL represents 2,2,5,5-tetramethyl-l-pyrrolidinyloxy), unambiguously demonstrated unidirectional binding of CBD to the tropocollagen analogues. Small angle x-ray scattering data revealed that CBD binds closer to a terminus for each of the five different tropocollagen analogues, which in conjunction with NMR titration studies, implies a binding mode where CBD binds to the C terminus of the triple helix.

The β subunits of voltage-gated Ca(2+) channels are best known for their roles in regulating surface expression and gating of voltage-gated Ca(2+) channel α(1) subunits. Recent evidence, however, indicates that these proteins have a variety of Ca(2+) channel-independent functions. For example, on the molecular level, they regulate gene expression, and on the whole animal level, they regulate early cell movements in zebrafish development. In the present study, an alternatively spliced, truncated β4 subunit (β4c) is identified in the human brain and shown to be highly expressed in nuclei of vestibular neurons. Pull-down assays, nuclear magnetic resonance, and isothermal titration calorimetry demonstrate that the protein interacts with the chromo shadow domain (CSD) of heterochromatin protein 1γ. Site-directed mutagenesis reveals that the primary CSD interaction occurs through a β4c C-terminal PXVXL consensus motif, adding the β4c subunit to a growing PXVXL protein family with epigenetic responsibilities. These proteins have multiple nuclear functions, including transcription regulation (TIF1α) and nucleosome assembly (CAF1). An NMR-based two-site docking model of β4c in complex with dimerized CSD is presented. Possible roles for the interaction are discussed.

Prion propagation involves a conformational transition of the cellular form of prion protein (PrPC) to a disease-specific isomer (PrPSc), shifting from a predominantly alpha-helical conformation to one dominated by beta-sheet structure. This conformational transition is of critical importance in understanding the molecular basis for prion disease. Here, we elucidate the conformational properties of a disulfide-reduced fragment of human PrP spanning residues 91-231 under acidic conditions, using a combination of heteronuclear NMR, analytical ultracentrifugation, and circular dichroism. We find that this form of the protein, which similarly to PrPSc, is a potent inhibitor of the 26 S proteasome, assembles into soluble oligomers that have significant beta-sheet content. The monomeric precursor to these oligomers exhibits many of the characteristics of a molten globule intermediate with some helical character in regions that form helices I and III in the PrPC conformation, whereas helix II exhibits little evidence for adopting a helical conformation, suggesting that this region is a likely source of interaction within the initial phases of the transformation to a beta-rich conformation. This precursor state is almost as compact as the folded PrPC structure and, as it assembles, only residues 126-227 are immobilized within the oligomeric structure, leaving the remainder in a mobile, random-coil state.

Objective Use T 2 mapping to evaluate the fatty infiltration of thigh muscles in Duchenne muscular dystrophy (DMD) patients, so as to analyze the value of T 2 mapping and T 2 relaxation time in the diagnosis of DMD. Methods Sixteen DMD patients who were admitted from January 2004 to January 2013 in our hospital and were diagnosed by clinical confirmation and gene detection have participated into this study. These 16 male patients formed the DMD group. Six age- and sex-matched healthy boys were selected as control group. Clinical functional scale, thigh axial T 1 WI-turbo spin echo (TSE), T 2 WI-TSE, spectral attenuated inversion recovery (SPAIR)-T 2 WI and T 2 mapping were performed in both 2 groups. T 1 WI fatty infiltration scale and T 2 relaxation time were assessed in adductor magnus, gracilis, adductor longus, sartorius, rectus femoris, vastus intermedius, vastus medialis, vastus lateralis, biceps femoris, semitendinosus and semimembranosus. Spearman rank correlation was conducted to assess the correlation between T 2 relaxation time and T 1 WI fatty infiltration scale or clinical functional scale. Results Compared with control group, the T 2 relaxation time of 8 muscles (adductor magnus, adductor longus, rectus femoris, vastus intermedius, vastus medialis, vastus lateralis, biceps femoris and semimembranosus) in DMD group were prolonged ( P < 0.05, for all). The longest average T 2 relaxation time was found in adductor magnus. The T 2 relaxation time of adductor magnus, vastus intermedius, vastus lateralis, biceps femoris, rectus femoris, adductor longus and vastus medialis was positively correlated with T 1 WI fatty infiltration scale ( P < 0.05, for all), and the T 2 relaxation time of adductor magnus and semimembranosus was positively correlated with clinical funetional scale ( P < 0.05, for all). A positive correlation was found in adductor magnus between T 2 relaxation time and both T1WI fatty infiltration scale ( r s = 0.867, P = 0.000) and clinical functional scale ( r s = 0.651, P = 0.005). Conclusions T 2 relaxation time could be used in the quantitative and objective analysis of DMD clinical severity, and adductor magnus was considered to be the most valuable muscle to reflect the clinical severity of DMD. DOI: 10.3969/j.issn.1672-6731.2015.06.004

The dsRNA-activated protein kinase (PKR) plays a major role in the cellular response to viral infection. PKR contains an N-terminal dsRNA binding domain (dsRBD) and a C-terminal kinase domain. The dsRBD consists of two tandem copies of a conserved double-stranded RNA binding motif, dsRBM1 and dsRBM2. dsRNA binding is believed to activate PKR by inducing dimerization and subsequent autophosphorylation reactions. We have characterized the function of the dsRBD by assessing the binding of dsRBM1 and dsRBD to a series of dsRNA sequences ranging from 15 to 45 bp. For dsRBM1, the binding stoichiometries agree with an overlapping ligand binding model where the motif binds to multiple faces of the dsRNA duplex and overlaps along the helical axis. Similar behavior is observed for a dsRBD containing both dsRBM1 and dsRBM2 for sequences up to 30 bp; however, the binding affinity is enhanced 30-fold. Longer dsRNA sequences exhibit lower-than-expected stoichiometries, indicating a change in binding mode. NMR spectroscopy was used to define the regions of the dsRBD that interact with dsRNA. dsRNA binding induces exchange broadening of cross-peaks in 1H-15N HSQC spectra. For a 20 bp dsRNA, the resonances most affected map to the known dsRNA binding regions of dsRBM1 as well as the N-terminus of dsRBM2. For a longer 40 bp sequence, additional regions of dsRBM2 exhibit enhanced broadening. These data support a model in which dsRBM1 plays the dominant role in binding short dsRNA sequences and dsRBM2 makes additional interactions with the longer sequences capable of activating PKR.

Magnetic resonance fingerprinting in multiple sclerosis

The lattice dynamics of solid 4He has been explored using pulsed NMR methods\nto study the motion of 3He impurities in the temperature range where\nexperiments have revealed anomalies attributed to superflow or unexpected\nviscoelastic properties of the solid 4He lattice. We report the results of\nmeasurements of the nuclear spin-lattice and spin-spin relaxation times that\nmeasure the fluctuation spectrum at high and low frequencies, respectively, of\nthe 3He motion that results from quantum tunneling in the 4He matrix. The\nmeasurements were made for 3He concentrations 16&lt;x_3&lt;2000 ppm. For 3He\nconcentrations x_3 = 16 ppm and 24 ppm, large changes are observed for both the\nspin-lattice relaxation time T_1 and the spin-spin relaxation time T_2 at\ntemperatures close to those for which the anomalies are observed in\nmeasurements of torsional oscillator responses and the shear modulus. These\nchanges in the NMR relaxation rates were not observed for higher 3He\nconcentrations.\n

Using the Fourier transform of the echo envelope, the proton line shapes, spin-lattice relaxation time, and spin-spin relaxation time have been measured in a (Ni0.36Nb0.24Zr0.40)90H10 glassy alloy at 1.83 T (∼78 MHz) and at temperatures between 1.8 and 300 K. First, the spectral line width decreases abruptly between 1.8 and 2.1 K. Next, it remains almost constant at 13 kHz up to ∼150 K. Finally, the line width decreases as the temperature increases from ∼150 to 300 K. The initial decrease in the spectral line width is ascribed to the distribution of the external field, which is caused by the penetration of vortices in the superconducting state. The subsequent leveling off in the spectral line width is ascribed to the dipole-dipole interaction between protons when hydrogen atoms are trapped into vacancies among the Zr-centered icosahedral Zr5Ni5Nb3 clusters. The final decrease in the spectral line width is ascribed to the motional narrowing of the width that is caused by the movement of hydrogen atoms. The temperature dependences of the spin-lattice and spin-spin relaxation time showed that at temperature above 150 K and the activation energy of 8.7 kJ/mol allowed the hydrogen atoms to migrate among the clusters. The distance between the hydrogen atoms is estimated to be 2.75 Å. Hydrogen occupancies among clusters in the (Ni0.36Nb0.24Zr0.40)90H10 glassy alloy play an important role in the diffusion behavior and in the electronic properties of this alloy.

We have developed a first‐principle method of calculating the spin–lattice relaxation time of excited electrons in metals based on the GW approach incorporating spin–orbit coupling. We have studied the spin–lattice relaxation time and path in Al, Cu, Au, Nb and Ta. The spin–lattice relaxation time and path in Nb appear to be much less than in Al, Cu, Au. They are particularly small in Ta, in accord with strong spin–orbit coupling.Comparing our results with experimental data on the impurity‐ and phonon‐induced spin relaxation times and path's, we find that at the energy about of 0.9 eV, which is typical for excited electrons in spin‐valve and magnetic‐tunnel transistors, the inelastic scattering accompanied by creation of electron–hole pairs is the dominating mechanism of spin–lattice relaxation. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

TiH x has been studied by pulsed NMR from 300K to 4.2K and SQUID CW NMR from 4.2K to 50mK. The proton spectra of TiH2 obtained by the two methods are identical and do not change in the whole temperature range. The line shape can be well described by the dipole-dipole interaction of protons as shown by a moment analysis. Below 100K, the spin-lattice relaxation time(T1) of TiH x , contains two contributions, one which obeys Korringa law and one constant term which is strongly influenced by magnetic impurities. The Korringa constant for TiH2 is 110±10K·s at high magnetic fields. Above 100K, the spin lattice relaxation time is influenced by the lattice distortion caused by thermal expansion which is in good agreement with former measurements.

The line shape measurements of the high-field high-frequency electron paramagnetic resonance transitions for paramagnetic ${\mathrm{Pb}}^{3+}$ in calcite performed at four frequencies between 95 and 285 GHz as function of temperature are reported. The linewidth analysis is based on a recent theory of relaxation for multilevel spin systems at high temperatures and is used to identify the spin lattice relaxation (SLR) mechanisms at such high microwave frequencies. In comparison with previous results obtained at lower microwave frequencies, this analysis emphasizes for a multilevel spin system two relevant new features: (a) the direct SLR process by modulation of the hyperfine interaction significantly contributes to the linewidths even at room temperature and (b) the SLR time of some simple transitions measured from the linewidth under conditions of negligible saturation could be very different from that measured by the continuous saturation method. The difference between the perpendicular-detected transitions and the parallel-detected transition concerning the contributions of the different SLR processes to the SLR times measured by the two methods mentioned above comes out to be very significant.

Variations in T1 and T2 relaxation times of normal appearing white matter and lesions in multiple sclerosis

Part one of this thesis consists of two sections. In the first section the fluorine chemical shift of a single crystal CaF_2 has been measured as a function of external pressure up to 4 kilobar at room temperature using multiple pulse NMR techniques. The pressure dependence of the shift is found to be -1.7 ± 1 ppm/kbar, while a theoretical calculation using an overlap model predicts a shift of -0.46 ppm/kbar. In the second section a separation of the chemical shift tensor into physically meaningful geometrical and chemical contributions is presented and a comparison of the proposed model calculations with recently reported data on hydroxyl proton chemical shift tensors demonstrates, that for this system, the geometrical portion accounts for the qualitative features of the measured tensors. Part two of the thesis consists of a study of fluoride ion motion in β-PbF_2 doped with NaF by measurement of the ^(19)F transverse relaxation time (T_2), spin lattice relaxation time (T_1) and the spin lattice relaxation time in the rotating frame (T_(1r)). Measurements over the temperature range of -50°C to 160°C lead to activation energies for T_1, T_(1r) and T_2 of 0.205 ± 0.01, 0.29 + 0.02 and 0.27 ± 0.01 ev/ion, and a T_(1r) minimum at 56°C yields a correlation time of 0.74 μsec. Pressure dependence of T_1 and T_2 yields activation volumes of <0.2 cm^3/g-mole and 1.76 ± 0.05 cm^3/g-mole respectively. These data along with the measured magnetic field independence of T_1 suggest that the measured T_1's are not caused by ^(19)F motion, but by thermally excited carriers. Part three of the thesis consists of a study of two samples of Th_4H_(15), prepared under different conditions but both having the proper ratio of H/Th (to within 1%). The structure of the Th_4H_(15) as suggested by X-ray measurements is confirmed through a moment analysis of the rigid lattice line shape. T_1 and T_2 measurements above 390 K furnish activation energies of 16.3 ± 1.2 kcal/mole and 18.0 ± 3.0 kcal/mole, respectively. Below 350 K, T_(1r) measurements furnish an activation energy of 10.9 ± 0.7 kcal/mole, indicating most probably more than a single mechanism for proton motion. A time-temperature hysteresis effect of the proton motion was found in one of the two samples and is strongly indicative of a phase change. T_1 at room temperature and below is dominated by relaxation due to conduction electrons with the product T_1T being 180 ± 10 K-sec. Using multiple pulse techniques to greatly reduce homonuclear dipolar broadening, a temperature-dependent line shift was observed, and the chemical shift anisotropy is estimated to be less than 16 ppm.

A global inversion method for multi-dimensional NMR logging

The toxicological impact of engineered nanoparticles in environmental or biological milieu is very difficult to predict and control because of the complexity of interactions of nanoparticles with the varied constituents in the suspended media. Nanoparticles are different from their bulk counterparts due to their high surface area-to-volume ratio per unit mass, which plays a vital role in bioavailability of these nanoparticles to its surroundings. This study explores how changes in the spin-spin nuclear relaxation time can be used to gauge the availability of surface area and suspension stability of selected nanoparticles (CuO, ZnO, and SiO2), in a range of simulated media. Spin-spin nuclear relaxation time can be mathematically correlated to wetted surface area, which is well backed up by the data of hydrodynamic size measurements and suspension stability. We monitored the change in spin-spin relaxation time for all the nanoparticles, over a range of concentrations (2.5 –100 ppm) in deionized water and artificial seawater. Selective concentrations of nanoparticle suspensions were subjected for temporal studies over a period of 48 hrs to understand the concept of spin-spin nuclear relaxation time-based reactivity of nanoparticle suspension. The nanoparticles showed high degree of agglomeration, when suspended in artificial seawater. This was captured by a decrease in spin-spin nuclear relaxation time and also an increment in the hydrodynamic size of the nanoparticles.