Introduction to magnetic resonance imaging

Diffusion NMR spectroscopy: folding and aggregation of domains in p53

Protein interactions and aggregation phenomena are probably amongst the most ubiquitous types of interactions in biological systems; they play a key role in many cellular processes. The ability to identify weak intermolecular interactions is a unique feature of NMR spectroscopy. In recent years, pulsed-field gradient NMR spectroscopy has become a convenient method to study molecular diffusion in solution. Since the diffusion coefficient of a certain molecule under given conditions correlates with its effective molecular weight, size, and shape, it is evident that diffusion can be used to map intermolecular interactions or aggregation events. Complex models can be derived from comparison of experimental diffusion data with those predicted by hydrodynamic simulations. In this review, we will give an introduction to pulsed-field gradient NMR spectroscopy and the hydrodynamic properties of proteins and peptides. Furthermore, we show examples for applying these techniques to a helical peptide and its hydrophobic oligomerization, as well as to the dimerization behavior and folding of p53.

Self- and mutual-diffusion coefficients measurements by 31P NMR 1D profiling and PFG-SE in dextran gels

31P NMR 1D profiling was successfully introduced to measure macroscale mutual-diffusion coefficients (D(m)) of phosphate ions in dextran gels. Series of 1D profiles describing the phosphate concentration along cylindrical dextran gels were acquired at different times. These profiles that included over 600 points could be fitted using equations derived from Fick's law, with D(m) as the single fitting parameter. Release and penetration profiles were recorded providing two alternative approaches for allowing the determination of D(m). The D(m) values were compared with microscale self-diffusion coefficients (D(s)) measured by pulsed field gradient spin echo (PFG-SE) technique. D(m) values, measured between 25 and 45 degrees C, were systematically lower than D(s). The experimental diffusion time and the associated diffusion length of D(s) (60 ms, 10 microm) are short compared to those of D(m) (up to 18 h, 50 mm). These scale differences are considered to be the origin of different D(s) and D(m) and provide information relative to the network in these gels.