Theory of nuclear spin relaxation in paramagnetic systems in solution

Kowalewski, Józef; Nordenskiöld, Lars; Benetis, Nikolas P.; Westlund, Per‐Olof

doi:10.1016/0079-6565(85)80007-8

Cited by 209 publications

(156 citation statements)

References 91 publications

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“…The same inconsistencies appear in the Abragam's treatment of translational relaxation 43 ; as pointed out by Hwang and Freed, correcting these problems leads to significant changes in the predicted relaxation rates. 41,56 Finally, it should be noted that Ullman's result for J(x) takes a form of a triple integral which cannot be easily evaluated because of severe singularities.…”

Section: Model 3: Diffusion In Harmonic Potentialmentioning

confidence: 99%

Paramagnetic relaxation enhancements in unfolded proteins: Theory and application to drkN SH3 domain

et al. 2009

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Site-directed spin labeling in combination with paramagnetic relaxation enhancement (PRE) measurements is one of the most promising techniques for studying unfolded proteins. Since the pioneering work of Gillespie and Shortle (J Mol Biol 1997;268:158), PRE data from unfolded proteins have been interpreted using the theory that was originally developed for rotational spin relaxation. At the same time, it can be readily recognized that the relative motion of the paramagnetic tag attached to the peptide chain and the reporter spin such as 1 H N is best described as a translation. With this notion in mind, we developed a number of models for the PRE effect in unfolded proteins: (i) mutual diffusion of the two tethered spheres, (ii) mutual diffusion of the two tethered spheres subject to a harmonic potential, (iii) mutual diffusion of the two tethered spheres subject to a simulated mean-force potential (Smoluchowski equation); (iv) explicit-atom molecular dynamics simulation. The new models were used to predict the dependences of the PRE rates on the 1 H N residue number and static magnetic field strength; the results are appreciably different from the Gillespie-Shortle model. At the same time, the Gillespie-Shortle approach is expected to be generally adequate if the goal is to reconstruct the distance distributions between 1 H N spins and the paramagnetic center (provided that the characteristic correlation time is known with a reasonable accuracy). The theory has been tested by measuring the PRE rates in three spin-labeled mutants of the drkN SH3 domain in 2M guanidinium chloride. Two modifications introduced into the measurement scheme-using a reference compound to calibrate the signals from the two samples (oxidized and reduced) and using peak volumes instead of intensities to determine the PRE rates-lead to a substantial improvement in the quality of data. The PRE data from the denatured drkN SH3 are mostly consistent with the model of moderately expanded random-coil protein, although part of the data point toward a more compact structure (local hydrophobic cluster). At the same time, the radius of gyration reported by Choy et al. (J Mol Biol 2002;316:101) suggests that the protein is highly expanded. This seemingly contradictory evidence can be reconciled if one assumes that denatured drkN SH3 forms a conformational ensemble that is dominated by extended conformations, yet also contains compact (collapsed) species. Such behavior is apparently more complex than predicted by the model of a random-coil protein in good solvent/poor solvent.Additional Supporting Information may be found in the online version of this article.Abbreviations: drkN SH3, N-terminal SH3 domain of the Drosophila adapter protein drk; EDTA, ethylenediaminetetraacetic acid; ESR, electron spin resonance; FRET, fluorescence resonance energy transfer; MTSL, methanethiosulfonate spin label; NOE, nuclear Overhauser effect; NAG, N-acetyl-glycine.

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Section: Model 3: Diffusion In Harmonic Potentialmentioning

confidence: 99%

Paramagnetic relaxation enhancements in unfolded proteins: Theory and application to drkN SH3 domain

et al. 2009

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“…[14,63,83] These equations are based, among other approximations, on the point-dipole approximation. [69] Other equations are available for slowly rotating complexes, taking into account a more adequate description of the electron spin relaxation due to zero-field splitting. [14,84,85] Nevertheless, all of them are still based on the point-dipole approximation for dipolar interaction, and they neglect spin-distribution effects.…”

Section: Dipolar Hyperfine Interactionmentioning

confidence: 99%

“…[25] However, a negative spin-polarization effect has been calculated for the f 7 ion Gd 3+ in complexes with one H 2 O or NH 3 molecule. [68] Hyperfine interactions are magnetic interactions, and the corresponding spin Hamiltonian can be written as shown in Equation (2): [69] H = S·A·I (2) where A is the 3 ϫ 3 HFI tensor, and S and I are the vectors of electron and nuclear spin, respectively. The HFI tensor is commonly split into an isotropic part and an anisotropic part, as given by Equation (3):…”

Section: Hyperfine Interactionsmentioning

confidence: 99%

Nuclear Spin Relaxation Parameters of MRI Contrast Agents – Insight from Quantum Mechanical Calculations

Yazyev

Helm

2007

Eur J Inorg Chem

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Keywords: Relaxivity / Hyperfine interactions / Quantum chemistry / Gadolinium / MRI contrast agent Nuclear magnetic relaxation in the presence of paramagnetic centres has gained increasing interest in recent years partly due to its importance for contrast agents in magnetic resonance imaging. Rational design of new more efficient agents is possible as a result of a better understanding of the underlying relaxation mechanisms. Quantum chemical calculations together with molecular dynamics simulations allow obtaining fundamental parameters such as quadrupole coupling constants and hyperfine interaction tensors directly at a molecular level. Recent results are presented on gadolinium(III) ions in aqueous solution and on [Gd(DOTA)(H 2 O)] -, a commercial MRI contrast agent. Isotropic hyperfine coupling

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“…Indeed, electronic relaxation is itself a function of rotational diffusion, which modulates the static crystal field in the laboratory frame. The consequences of this correlation are twofold (Kowalewski et al, 1985): (i) cross relaxation effects appear between the nuclear dipolar relaxation and the electron relaxation, and (ii) cross terms also appear between the dipolar and scalar relaxation processes. We can overlook (i) since it only affects the transverse nuclear relaxation (Benetis et al, 1983a), and thus plays no role in our study of 1 H relaxation where only T 1 is considered.…”

Section: T G T G T I T Dt I G T G T I T Dt I J Tmentioning

confidence: 99%