Dynamics of Solid Proteins by Means of Nuclear Magnetic Resonance Relaxometry

Abstract

1H Nuclear magnetic resonance (NMR) relaxometry was exploited to investigate the dynamics of solid proteins. The relaxation experiments were performed at 37 °C over a broad frequency range, from approximately 10 kHz to 40 MHz. Two relaxation contributions to the overall 1H spin–lattice relaxation were revealed; they were associated with 1H–1H and 1H–14N magnetic dipole–dipole interactions, respectively. The 1H–1H relaxation contribution was interpreted in terms of three dynamical processes occurring on timescales of 10−6 s, 10−7 s, and 10−8 s, respectively. The 1H–14N relaxation contribution shows quadrupole relaxation enhancement effects. A thorough analysis of the data was performed revealing similarities in the protein dynamics, despite their different structures. Among several parameters characterizing the protein dynamics and structure (e.g., electric field gradient tensor at the position of 14N nuclei), the orientation of the 1H–14N dipole–dipole axis, with respect to the principal axis system of the electric field gradient, was determined, showing that, for lysozyme, it was considerably different than for the other proteins. Moreover, the validity range of a closed form expression describing the 1H–14N relaxation contribution was determined by a comparison with a general approach based on the stochastic Liouville equation.

Towards applying NMR relaxometry as a diagnostic tool for bone and soft tissue sarcomas: a pilot study

“…The other parameters associated with QRE, namely , , , and , did not show significant differences. Comparing with other publications investigating QRE in proteins (bovine serum albumin, albumin from human plasma, elastin and lysozyme) 26 , the quadrupole parameters confirm the current model stating that the QRE are associated with 14 N nuclei of protein backbones 23 , 48 , 49 . In both tissues and proteins the correlation time characterizing the fluctuations of the 1 H– 14 N dipole–dipole coupling was about 1 µs within 20% error, independently of the values of the correlation times for tissues, or in solid (dry) proteins investigated in the literature.…”

“…This may indicate that mainly reflects the quadrupole relaxation time originating from local fluctuations of the electric field gradient tensor at the 14 N site, which are not specific. However, the effective 1 H– 14 N distance for tissues, , was found to vary between 3.1 and 3.7 Å which is much larger than for solid proteins (1.65–1.7 Å) 26 . This effect may be caused by the presence of water molecules in the vicinity of the protein backbones, possibly increasing the 1 H to 14 N ratio involved in the QRE.…”

“…NMR relaxometry has been intensively expanding in recent years, offering interesting applications in physics and chemistry for liquid 11 – 13 , macromolecular (polymers, proteins) 6 , 11 , 13 – 15 and solid state systems 16 – 19 , including the possibility of modelling the relaxation enhancement for paramagnetic contrast agents 20 – 22 . Relaxation dispersion profiles for protein systems also show frequency-specific relaxation maxima, referred to as quadrupole peaks 23 – 26 , an effect referred to as Quadrupole Relaxation Enhancement (QRE) 16 – 19 , 23 – 28 , the physical origin of which is well understood 16 , 27 , 28 . In biological systems QRE is due to the presence of 14 N nuclei in proteins where motion is restrained as a result of cross-linking or aggregation, for example.…”

Dynamics of Ionic Liquids in Confinement by Means of NMR Relaxometry—EMIM-FSI in a Silica Matrix as an Example

“…In both cases, for 1 H and 19 F, the relaxation data at 238 K and above show a weak dispersion (become dependent on the resonance frequency only in the high frequency range), in contrast to the data at 233 K, that show not only a strong dispersion but also effects referred to as quadrupole relaxation enhancement (QRE) [ 11 , 32 , 33 , 34 , 35 , 36 , 37 , 38 ]. The QRE effects originate from dipole–dipole couplings between 1 H and 14 N nuclei in the case of the cation and 19 F and 14 N nuclei in the case of the anion.…”

“…Thus, at some magnetic fields, the 1 H (or 19 F) resonance frequency matches one of the transition frequencies of the 14 N nuclei. For the spin quantum number S = 1, this happens at the following frequencies [ 34 , 35 , 36 , 37 , 38 ]: , and , where and denote the amplitude and the asymmetry parameter of the quadrupole coupling, respectively. The amplitude is defined as: = , where Q denotes the quadrupole moment of the nucleus, while q is the zz component of the electric field gradient tensor.…”