Nuclear magnetic resonance studies of chloride binding to proteins

Bull, Thomas; Norne, Jan Erik; Reimarsson, Pétur; Lindman, Björn

doi:10.1021/ja00483a001

Cited by 25 publications

(19 citation statements)

References 5 publications

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“…Such an analysis gave us a consistent correlation time at different spectrometer frequencies. A distinction between the relaxation of unbound ions in protein solutions and in salt solutions was done previously by Bull et al (8) for chloride ions. In their system they were able to measure it directly by displacing the chloride ions bound to HSA using dodecyl sulfate.…”

Section: Discussionmentioning

confidence: 99%

“…(8) showed that these linear approximations are valid as long as war, < 1.5, and in cases where a large excess of free hydrated ions is in fast exchange with quadrupolar nuclei bound at sites with long correlation times. The linear approximation is strictly valid for Tj/T{ and T$/TJ ratios close to unity, or when the initial part of the decay curves is considered.…”

Section: Pimentioning

confidence: 99%

“…As an approximation for T$ we suggest using the values of T I since, within the theory given in Eqs. [4]- [8], (T;)-' is the average between (T;)-l and (T{)-'; and in cases where the contribution of (To)-1 is large, TS and TI become equal.…”

Section: Pimentioning

confidence: 99%

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Sodium‐23 NMR relaxation times in body fluids

Shinar¹

1986

Magnetic Resonance in Med

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23Na longitudinal and transverse NMR relaxation times were measured in human serum, plasma, cerebrospinal fluid (CSF), and solutions of plasma proteins. The magnetization decay curves could not be resolved into two exponentials. A procedure to extract quantitative information from the measured relaxation rates in such a case was developed. The relaxation times of 23Na in serum and plasma were analyzed in terms of the different contributions from free Na+, Na+ bound to small molecules, and Na+ bound to various protein fractions in these body fluids. While T1 is essentially that of free Na+ in a solution which is slightly more viscous than salt solution, T2 is influenced by binding to proteins with the largest contribution from serum albumin. The effect of binding to small molecules on T1 and T2 is negligible. From measurements of the relaxation times at several magnetic field strengths a rotational correlation time of Na+ bound to serum albumin of 16 +/- 6 ns was obtained. The fraction of bound Na+ in serum and plasma was roughly estimated as 0.02% of the total sodium. The relaxation times in cerebrospinal fluid are very similar to those of NaCl solution.

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Section: Discussionmentioning

confidence: 99%

Section: Pimentioning

confidence: 99%

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Sodium‐23 NMR relaxation times in body fluids

Shinar¹

1986

Magnetic Resonance in Med

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“…The first, the wobbling in a cone model [23,24], permits simple diffusion of a rotation axis inside a cone. This model has been applied to the relaxation analysis of methyl groups of the bovine pancreatic trypsin inhibitor [17].…”

Section: Discussionmentioning

confidence: 99%

Structural Dynamics of Erabutoxin b

Inagaki

Miyazawa

Tamiya

et al. 1982

European Journal of Biochemistry

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A detailed examination has been made of tlie I3C NMR relaxation times of the assigned methyl groups of erabutoxin b. Anisotropic rotation was analysed using a restricted diffusion model. The results are compared with a previous study of the 'H NMR relaxation times. There is good agreement on the segments of the molecule which show restricted motion. Our results are compared with those of previous studies on proteins in solution and in crystals and again tlie general agreement is good. We have attempted to interpret the value of the limited motion seen in tlie protein to the reactions of the neurotoxin.Much experimental evidence shows that there is considerable internal motion in proteins in solution [I -31 (and references cited in [3]), in agreement with theoretical treatments of protein dynamics which indicate that there are internal motion in the 1 -100-ps range [4,5]. The idea that a protein has a dynamic flexible structure would seem to be especially important for the rate of protein-protein interaction where two complicated surfaces must come together. We have pointed out that a study of neurotoxins which bind to membrane receptor proteins could provide a good test case. We have therefore chosen to examine erabutoxin b, a small protein with 62 amino acids, in detail by NMR methods in order to see if molecular motion is important for its binding steps to the acetylcholine receptor protein. We started this work using proton NMR and, in a previous paper, we have reported the analysis of the relaxation behaviour of methyl protons in erabutoxin b [6]. There is a methodological difficulty, however, in that tlie contribution of external protons to the relaxation of methyl groups has to be analysed in addition to the dynamics of the methyl groups themselves. Despite these difficulties, the 'H relaxation study generated considerable knowledge about the motion of the methyl groups in the protein. In contrast, I3C relaxation times are dominantly determined by the nearest proton(s) and interpretation of relaxation in terms of molecular motions is then more direct [7]. In the present study, we report the relaxation behaviour of the methyl carbons in erabutoxin b and elucidate tlie segmental motion of its side chains. Unfortunately these 13C NMR studies have had to be made in non-dilute solutions which could affect relaxation processes of surface residues. Thus a comparison with tlie proton NMR observation is very valuable. It will be shown here that the two studies of methyl group motion in erabutoxin b give very similar results. We can then comment on the possible functional importance of these motions. EXPERIMENTAL PROCEDUREErabutoxin b was isolated from tlie venom of Laticauda .scwz@i.sc.iti/u as described previously [8]. After purification, Ahhrrviutions. T I , spin-lattice relaxation time; NOE, nuclear Overhauser effect.-~ it was lyophilized from 0.1 M acetic acid solution. For NMR measurements, samples of erabutoxin b were dissolved in 99.5 % 2H20 to a concentration of 20 mM. The pH of the samples was adjusted to ...

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“…times the resonance frequency in radiandsec, wfLLn, versus the actual correlation time times the resonance frequency, w. The numbers associated with each curve correspond to the fraction of l/Tl, which is associated with the free ions. The straight line corresponds to the wrun = 07 (from Bull et al, 1978).…”

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confidence: 99%