Biomedical subjects

Beat H Meier

Publications and source records attributed to Beat H Meier.

24 records · Page 2Linked to original sources

PubMed2003

Fast-MAS total through-bond correlation spectroscopy using adiabatic pulses.

Pulse sequences consisting of adiabatic pulses for total through-bond correlation spectroscopy (TOBSY) under magic-angle spinning (MAS) are introduced. Above a certain threshold, the polarization transfer achieved with these sequences is largely insensitive to the amplitude and homogeneity of the radiofrequency field employed. An experimental transfer efficiency of up to 76% was achieved in a two-spin system using the sequence WiW9(24)(1) at a MAS frequency of 26.67 kHz. Applications to resonance assignments in the dipeptide L-Val-L-Phe and in the cyclic decapeptide antamanide are demonstrated.

Algorithms↗

PubMed2003

Inverse methods in two-dimensional NMR spectral analysis.

Solid-state NMR is a valuable technique for the study of disordered materials. Analysis of such spectra usually involves solution of so-called ill-posed inverse problems. Here we present a strategy for the analysis of two-parameter two-dimensional NMR problems and test it on 2D DECODER and DOQSY experiments. Using Monte Carlo tests, constraints are determined for the resolution and accuracy of the analysis for both experiments. The methods are finally applied to spectra of spider dragline silk, a heterogeneous solid fibrous protein.

Animals↗

PubMed2003

Low-power XiX decoupling in MAS NMR experiments.

Low-power XiX proton decoupling under fast magic-angle spinning is introduced. The method is applicable if the MAS frequency exceeds the proton-proton interactions. For rigid organic solids this is the case for MAS frequencies above approximately 40 kHz. It is shown that the quality of the decoupling as well as the sensitivity to frequency offsets can be improved compared to low-power continuous-wave decoupling. The decoupling efficiency is somewhat reduced compared to optimized high-power decoupling: in a peptide sample investigated at an MAS frequency of 50 kHz a loss of about 10% in signal intensity for CH3 and CH groups, and of about 40% for CH2 groups was observed. Taking into consideration, that the rf amplitude in the low-power XiX was about 15 times lower than in high-power XiX decoupling, such a reduction in line intensity is sometimes tolerable.

Carbon Isotopes↗

PubMed2003

NMR of bicelles: orientation and mosaic spread of the liquid-crystal director under sample rotation.

Model-membrane systems composed of liquid-crystalline bicellar phases can be uniaxially oriented with respect to a magnetic field, thereby facilitating structural and dynamics studies of membrane-associated proteins. Here we quantitatively characterize a method that allows the manipulation of the direction of this uniaxial orientation. Bicelles formed from DMPC/DHPC are examined by (31)P NMR under variable-angle sample-spinning (VAS) conditions, confirming that the orientation of the liquid-crystalline director can be influenced by sample spinning. The director is perpendicular to the rotation axis when Theta (the angle between the sample-spinning axis and the magnetic field direction) is smaller than the magic angle, and is parallel to the rotation axis when Theta is larger than the magic angle. The new (31)P NMR VAS data presented are considerably more sensitive to the orientation of the bicelle than earlier (2)H studies and the analysis of the sideband pattern allows the determination of the orientation of the liquid-crystal director and its variation over the sample, i.e., the mosaic spread. Under VAS, the mosaic spread is small if Theta deviates significantly from the magic angle but becomes very large at the magic angle.

Dimyristoylphosphatidylcholine↗

PubMed2003

Switched-angle spinning applied to bicelles containing phospholipid-associated peptides.

In a model study, the proton NMR spectrum of the opioid pentapeptide leucine-enkephalin associated with bicelles is investigated. The spectral resolution for a static sample is limited due to the large number of anisotropic interactions, in particular strong proton-proton couplings, but resolution is greatly improved by magic-angle sample spinning. Here we present two-dimensional switched-angle spinning NMR experiments, which correlate the high-resolution spectrum of the membrane-bound peptide under magic-angle spinning with its anisotropic spectrum, leading to well-resolved spectra. The two-dimensional spectrum allows the exploitation of the high resolution of the isotropic spectrum, while retaining the structural information imparted by the anisotropic interactions in the static spectrum. Furthermore, switched-angle spinning techniques are demonstrated that allow one to record the proton spectrum of ordered bicellar phases as a function of the angle between the rotor axis and the magnetic field direction, thereby scaling the dipolar interactions by a predefined factor.

Dimyristoylphosphatidylcholine↗

PubMedDate not supplied

NMR characterization of native liquid spider dragline silk from Nephila edulis.

Solid spider dragline silk is well-known for its mechanical properties. Nonetheless a detailed picture of the spinning process is lacking. Here we report NMR studies on the liquid silk within the wide sac of the major ampullate (m.a.) gland from the spider Nephila edulis. The resolution in the NMR spectra is shown to be significantly improved by the application of magic-angle spinning (MAS). From the narrow width of the resonance lines and the chemical shifts observed, it is concluded that the silk protein within the wide sac of the m.a. gland is dynamically disordered throughout the molecule in the sense that each amino acid of a given type senses an identical environment, on average. The NMR data obtained are consistent with an isotropic liquid phase.

Animals↗