Molecular Motions and Interactions in Aqueous Solutions of Thymosin-ß4 , Stabilin CTD and Their 1 : 1 Complex, Studied by 1 H-NMR Spectroscopy.

Wide-line 1 H NMR measurements were extended and all results were interpreted in a thermodynamics-based new approach on aqueous solutions of thymosin-ß4 (Tß4 ), stabilin cytoplasmic domain (CTD), and their 1 : 1 complex. Energy distributions of potential barriers controlling the motion of protein-bound water molecules were determined. Heterogeneous and homogeneous regions were found in the protein-water interface. The measure of heterogeneity of this interface gives quantitative value for the portion of disordered parts in the protein. Ordered structural elements were found extending up to ∼20 % of the individual whole proteins. About 40 % of the binding sites of free Tß4 get involved in bonds holding the complex together. The complex has the most heterogeneous solvent accessible surface (SAS) in terms of protein-water interactions. The complex is more disordered than Tß4 or stabilin CTD. The greater SAS area of the complex is interpreted as a clear sign of its open structure.

Wide-line NMR and protein hydration.

In this chapter, the reader is introduced to the basics of wide-line NMR, with particular focus on the following: (1) basic theoretical and experimental NMR elements, necessary before switching the spectrometer and designing the experiment, (2) models/theories for the interpretation of measured data, (3) definition of wide-line NMR spectrometry, the description of the measurement and evaluation variants, useful hints for the novice, (4) advice on selecting the solvent, which is not a trivial task, (5) a note of warning that not all data are acceptable in spite of the statistical confidence. Finally, we wrap up the chapter with the results on two proteins (a globular and an intrinsically disordered).

Distinct hydration properties of wild-type and familial point mutant A53T of α-synuclein associated with Parkinson's disease.

The propensity of α-synuclein to form amyloid plays an important role in Parkinson's disease. Three familial mutations, A30P, E46K, and A53T, correlate with Parkinson's disease. Therefore, unraveling the structural effects of these mutations has basic implications in understanding the molecular basis of the disease. Here, we address this issue through comparing details of the hydration of wild-type α-synuclein and its A53T mutant by a combination of wide-line NMR, differential scanning calorimetry, and molecular dynamics simulations. All three approaches suggest a hydrate shell compatible with a largely disordered state of both proteins. Its fine details, however, are different, with the mutant displaying a somewhat higher level of hydration, suggesting a bias to more open structures, favorable for protein-protein interactions leading to amyloid formation. These differences disappear in the amyloid state, suggesting basically the same surface topology, irrespective of the initial monomeric state.

Hydration water/interfacial water in crystalline lens.

Wide-line (1)H NMR signal intensity, spin-lattice and spin-spin relaxation rates and differential scanning calorimetry (DSC) measurements were done on avian (chicken and turkey) crystalline lenses between -70 degrees C and +45 degrees C to provide quantitative measures of protein hydration characteristic of the protein-water interfacial region. These measures are of paramount importance in understanding both the physiology of crystalline lens and its transitions to the cataractous pathological state characterized by the formation of opaque protein aggregates. Water mobility shows a characteristic transition at about -60 degrees C, which is identified as the melting of the interfacial/hydrate water. The amount of water in the low-temperature mobile fraction is about h = 0.4 g water/g protein, which equals the hydration required for protein activity. The amount of mobile water is temperature-independent up to about -10 degrees C, with a significant increase at higher temperatures below 0 degrees C. Above 0 degrees C, the relaxation processes can be described by a single (for spin-lattice) and by a triple (for spin-spin relaxation) exponential function. The spin-spin relaxation rate component of R(2) = 10-20 s(-1) and its dynamical parameters characterize the interfacial water at ambient or physiological temperatures. When considered an independent phase, the specific heat of the hydrate water obtained by a combination of DSC and NMR data in the temperature range -43 degrees C to -28 degrees C is higher than that of pure/bulk water. This discrepancy can only be resolved by assuming that the hydrate water is in strong thermodynamic coupling with the protein matrix. The specific heat for the system composed of the protein molecule and its hydration water is 4.6 +/- 0.3 J g(-1) K(-1). Thus, in a thermodynamic sense, crystalline protein and its hydrate layer behave as a highly-interconnected single phase.

Protein-water and protein-buffer interactions in the aqueous solution of an intrinsically unstructured plant dehydrin: NMR intensity and DSC aspects.

Proton NMR intensity and differential scanning calorimetry measurements were carried out on an intrinsically unstructured late embryogenesis abundant protein, ERD10, the globular BSA, and various buffer solutions to characterize water and ion binding of proteins by this novel combination of experimental approaches. By quantifying the number of hydration water molecules, the results demonstrate the interaction between the protein and NaCl and between buffer and NaCl on a microscopic level. The findings overall provide direct evidence that the intrinsically unstructured ERD10 not only has a high hydration capacity but can also bind a large amount of charged solute ions. In accord, the dehydration stress function of this protein probably results from its simultaneous action of retaining water in the drying cells and preventing an adverse increase in ionic strength, thus countering deleterious effects such as protein denaturation.

1H spin-spin relaxation in normal and cataractous human, normal fish and bird eye lenses.

A systematic study on nuclear spin-spin relaxation of water protons in human, fish and bird eye lenses/lens nuclei is reported. The purpose of this study is to clarify the real nature of the relaxation processes not describable as a single exponential decay. The characterization of the spin-spin relaxation by a single exponential is commonly used both in literature and in MRI diagnostics. However, in our opinion, this single exponential decay hypothesis is an oversimplification that can lead to the loss of essential information. Our measurements were performed by Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences on human, carp, chicken and turkey eye lenses/lens nuclei. Several hundreds of CPMG echo amplitude were detected and the time-dependence of their decay was determined by careful fitting procedures. Our results clearly rule out the single exponential decay hypothesis for eye lenses: at least two or three decaying components are observed. These phenomena need further investigations: it should be decided which of the relaxation parameters, T2I-s and A(i)-s gives the most characteristic physiological or pathological information. It is claimed that the amplitude ratio of the bound and the free water fraction carries the most characteristic information. During the cataract formation the weight of free water is raised by more than 25%.

Variability of magnetic resonance parameters in pituitary adenomas at low temperature.

Temperature dependent spin-lattice relaxation time, T1, measurements were carried out on surgically removed pituitary adenoma tissues at low temperature. Differences were found between samples; the temperature dependence of T1 showed a broad minimum below freezing. The measured data were fitted by theoretical lines to determine various parameters such as activation energy, correlation time and intensity.

Progressive saturation relaxation spectroscopy. Investigations on lens nucleus and cortex at low temperature.

A systematic study of the temperature dependence of progressive saturation relaxation spectra was carried out on the nucleus and cortex of normal and cataractous eye lenses at different temperatures below freezing. A more complicated fine structure was detected, than was previously thought. The method utilized may well be applied in tomography as well.

In vitro assessment of MR relaxation properties of pituitary adenomas.

Proton magnetic relaxation times (T1 and T2) and bound water content were measured in vitro in pituitary adenomas from 15 patients using 90 MHz radiofrequency excitation. These data were compared with those measured in normal pituitary glands obtained from four cats and seven fresh human cadavers. The T1 and T2 measured at 24 degrees C in the tumors (mean +/- SD: 1,170 +/- 80 and 123 +/- 35 ms, respectively) were significantly higher than those of cadaver pituitary (830 +/- 200 and 76 +/- 12 ms) and cat pituitary gland (790 +/- 120 and 69 +/- 10 ms). Although the absolute values were lower, similar differences were present in T1 measured at 4 degrees C. Two-dimensional T2 versus T1 plot was particularly helpful in distinguishing tumor from the normal gland. When tumors were grouped according to density on CT, histology or previous treatment (e.g., irradiation or bromocriptine), there were no significant differences in T1 values between the groups. Bound water content was not found to correlate with T1 or T2 values. We concluded that pituitary adenomas can be distinguished from normal pituitary glands by their different relaxation properties when measured at high frequency in vitro MR.

1H nuclear magnetic resonance study of intervertebral discs. A preliminary report.

In vitro 1H pulse nuclear magnetic resonance (NMR) studies on human intervertebral disc tissues were performed to establish the characteristics of relaxation processes. The spin-lattice relaxation time, bound water and dry matter content were measured. Biopsy material from fresh cadavers was taken from different discs along the spinal column and from different sectors of some single discs. It is suggested that the measured parameters correlate with the biomechanical behavior of discs, which in turn is influenced by function, by exposure to physical stresses, or by aging.

In vitro 1H NMR "mapping" of human intervertebral discs.

Human intervertebral discs were investigated by 1H NMR in vitro. The measured parameters of samples differently located in discs give the "maps" of discs. The spin-lattice relaxation-time maps show similar structure to dry matter and bound water maps, which might mean the future possibility to detect certain disc processes via accurate T1 images.

Combined 1H-NMR and vacuum dehydration study of rat muscles.

Combined NMR and the vacuum dehydration method were used to study the state of water in rat muscle. Comparative studies were carried out on muscles of young and old mature white rats. The spin-lattice relaxation time was measured as a function of water content. The single-exponential behaviour of the relaxation process indicates a normal fast-exchange process between the different fractions. The more elaborate analysis demonstrates the failure of the original fast-exchange model. It is proved that structural changes take place in the macromolecule/ion/bound water system of the muscle even at the beginning of dehydration. All the muscle water seems to be necessary to maintain the normal natural state of the muscle's molecular structure.

Water fractions in normal and senile cataractous eye lenses studied by NMR.

The state of water and water fractions in normal and senile cataractous eye lenses was studied by the NMR method. Combining NMR with vacuum dehydration provided additional information on multifractional samples. A new mathematical procedure is presented which separates the characteristic parameters of the different fractions and helps to determine the relaxation times and amounts of the fractions. The measurement accuracy enables separation of three different water fractions both in normal and in cataractous lenses.