Hyper-mobile Water Research Articles

Hyper-mobile Water and Raman 2900 cm-1 Peak Band of Water Observed around Backbone Phosphates of Double Stranded DNA by High-Resolution Spectroscopies and MD Structural Feature Analysis of Water.

High-resolution measurements of microwave dielectric relaxation and Raman spectroscopies for waters in double-stranded (ds) 10-mer DNA solution revealed the presence of hyper-mobile water (HMW) and a marked OH stretching band appearing in the range from 2500 to 3100 cm-1, here called the LA band, at the low wavenumber tail of the major OH stretching band of water. Quantitation of the Raman scattering intensity for ds 10-mer DNA in phosphate or tris(hydroxymethyl)aminomethane (TRIS) buffers showed that the LA band was formed by 2000-3000 water molecules per ds 10-mer DNA, indicating collective OH stretching vibrations of water molecules around the backbone phosphate oxygen atoms. The LA band intensity of ds 10-mer DNA in 10 mM TRIS increased and decreased by 30% with the addition of 2 mM MgCl2 and 2 mM CaCl2, respectively. The LA band intensity and the effect of adding Mg(II) or Ca(II) ions to the band intensity were maintained in the presence of 0.14 M KCl; however, the changes induced by the divalent cations were reduced by half. Molecular dynamics calculations of water molecules around the backbone phosphate groups of ds 10-mer DNA indicate the presence of high-density water and broad regions of fluctuating water density, suggesting that they correspond to HMW and the LA band, respectively.

Strong Dependence of Hydration State of F-Actin on the Bound Mg2+/Ca2+ Ions

Understanding of the hydration state is an important issue in the chemomechanical energetics of versatile biological functions of polymerized actin (F-actin). In this study, hydration-state differences of F-actin by the bound divalent cations are revealed through precision microwave dielectric relaxation (DR) spectroscopy. G- and F-actin in Ca- and Mg-containing buffer solutions exhibit dual hydration components comprising restrained water with DR frequency f2 (<fw: DR frequency of bulk solvent, 17 GHz at 20 °C) and hypermobile water (HMW) with DR frequency f1 (>fw). The hydration state of F-actin is strongly dependent on the ionic composition. In every buffer tested, the HMW signal Dhyme (≡ (f1 - fw)δ1/(fwδw)) of F-actin is stronger than that of G-actin, where δw is DR-amplitude of bulk solvent and δ1 is that of HMW in a fixed-volume ellipsoid containing an F-actin and surrounding water in solution. Dhyme value of F-actin in Ca2.0-buffer (containing 2 mM Ca(2+)) is markedly higher than in Mg2.0-buffer (containing 2 mM Mg(2+)). Moreover, in the presence of 2 mM Mg(2+), the hydration state of F-actin is changed by adding a small fraction of Ca(2+) (∼0.1 mM) and becomes closer to that of the Ca-bound form in Ca2.0-buffer. This is consistent with the results of the partial specific volume and the Cotton effect around 290 nm in the CD spectra, indicating a change in the tertiary structure and less apparent change in the secondary structure of actin. The number of restrained water molecules per actin (N2) is estimated to be 1600-2100 for Ca2.0- and F-buffer and ∼2500 for Mg2.0-buffer at 10-15 °C. These numbers are comparable to those estimated from the available F-actin atomic structures as in the first water layer. The number of HMW molecules is roughly explained by the volume between the equipotential surface of -kT/2e and the first water layer of the actin surface by solving the Poisson-Boltzmann equation using UCSF Chimera.

Comparative Study on the Properties of Hydration Water of Na- and K-Halide Ions by Raman OH/OD-stretching Spectroscopy and Dielectric Relaxation Data

Properties of hypermobile water (HMW) were studied by Raman OH-stretching spectroscopy. Hydration water properties measured by Raman OH-stretching spectra of NaX/KX (X: Cl, Br, I) solutions (0.05-0.2 M) were comparatively analyzed with the data by dielectric relaxation spectroscopy (DRS), NMR, and statistical mechanical studies. The Raman OH-stretching spectra were well-fitted with linear combinations of the spectra of pure water both at the same and the higher temperatures. The fitting analysis determined the "structure temperature" Tstr and mole fraction of the high Tstr water region, giving the hydration number Nhyd, for each electrolyte solution. The determined Tstr was much higher than the solution temperature of 293 K for each tested salt and was higher for larger halide ions, consistent with commonly known "structure-breaking" order Cl < Br < I. No significant differences in Nhyd were observed between NaX and KX and among even halide ion species within the experimental errors. Measured Nhyd values of 25-27 were much greater than the reported numbers by NMR chemical shift and (17)O NMR relaxation studies and comparable to the numbers of hypermobile water reported in the previous DRS studies. The results indicated that the hydration region around NaX or KX measured by the present Raman study was nearly overlapped with the region of HMW by DRS. It was also suggested that differences in the ion size effects on Tstr and the DR frequency resulted from the sensitivity difference to long-range many-body interactions among water molecules. High structure-temperature regions were also detected by the analysis of OH-stretching and OD-stretching bands for 0.2 M NaI in H2O/D2O mixed solvent of 50 mol %, and we found that both OH-stretching and OD-stretching bands have almost equivalent Tstr ≈ 330 K and mole fractions with each other.

What is “hypermobile” water?: detected in alkali halide, adenosine phosphate, and F-actin solutions by high-resolution microwave dielectric spectroscopy

Abstract Experimental observation by high-resolution microwave dielectric spectroscopy of hydration properties of alkali halide ions, adenosine phosphate ions, and F-actin revealed the existence of hypermobile water (HMW) molecules around those solutes. To understand the molecular process of HMW, two theoretical approaches are reviewed here. One is based on a statistical mechanical approach to analyze the rotational freedom of water molecules around a charged particle. Another approach reports direct calculation of dielectric relaxation process of water molecules around an ion. Experimentally observed HMW molecules are theoretically explained with the significance of multi-correlations among an ion and water molecules.

3P133 NaCl、NaI水溶液におけるハイパーモバイル水の熱容量及び密度の評価(07. 水・水和/電解質,ポスター,第52回日本生物物理学会年会(2014年度))

3P133 NaCl、NaI水溶液におけるハイパーモバイル水の熱容量及び密度の評価(07. 水・水和/電解質,ポスター,第52回日本生物物理学会年会(2014年度))

Anion-Dependence of Fast Relaxation Component in Na-, K-Halide Solutions at Low Concentrations Measured by High-Resolution Microwave Dielectric Spectroscopy

High-resolution microwave dielectric spectra of NaX, KX (X: F, Cl, Br, I) aqueous solutions of c = 0.05 and 0.1 M measured in the frequency range 0.2-26 GHz at 10 °C are analyzed. The dielectric relaxation (DR) spectrum of each solution, which deviates slightly from the bulk-water spectrum, is mathematically divided into the bulk-water spectrum and the spectrum of solute particles covered with a water layer using a mixture theory by assuming the existence of continuous bulk-water phase. The solute spectra above 3 GHz are fitted with a linear series of pure water component (γ dispersion with DR frequency fw), fast Debye component-1 with DR frequency f1 (>fw), and slow Debye component-2 with DR frequency f2 (<fw). Component-2 is only found for the fluorides. The sum of dispersion amplitudes of γ and components -1 and -2 for NaX and KX are found to be almost irrespective of X and equal to the pure water level, indicating that components -1 and -2 are from the water modified by ions, thus denoted as "hypermobile water" and "constrained water" (not rigidly bound to ion), respectively. Below 3 GHz, sub-GHz dispersion component is detected and assigned as a relaxation response of counterion cloud. The resulting limiting-molar conductivities of NaX and KX are in good agreement with the literature data measured at much lower frequencies. The estimated number of hypermobile water molecules is found to increase from 9 to 31 for NaX and from 9 to 37 for KX with increasing anion size. Thus, except for the fluorides, it is reported that the modified water by salt ions exhibits only Debye component-1 other than γ dispersion, indicating the existence of a water-ions collective hypermobile mode in each solution.

Difference in hydration structures between F-actin and myosin subfragment-1 detected by small-angle X-ray and neutron scattering.

Hydration structures around F-actin and myosin subfragment-1 (S1), which play central roles as counterparts in muscle contraction, were investigated by small-angle X-ray scattering (SAXS) and small-angle neutron scattering (SANS). The radius of gyration of chymotryptic S1 was evaluated to be 41.3±1.1 Å for SAXS, 40.1±3.0 Å for SANS in H2O, and 37.8±0.8 Å for SANS in D2O, respectively. The values of the cross-sectional radius of gyration of F-actin were 25.4±0.03 Å for SAXS, 23.4±2.4 Å for SANS in H2O, and 22.6 ± 0.6 Å for SANS in D2O, respectively. These differences arise from different contributions of the hydration shell to the scattering curves. Analysis by model calculations showed that the hydration shell of S1 has the average density 10–15% higher than bulk water, being the typical hydration shell. On the other hand, the hydration shell of F-actin has the average density more than 19% higher than bulk water, indicating that F-actin has a denser, unusual hydration structure. The results indicate a difference in the hydration structures around F-actin and S1. The unusual hydration structure around F-actin may have the structural property of so-called “hyper-mobile water” around F-actin.

Hydration-State Change of Horse Heart Cytochrome c Corresponding to Trifluoroacetic-Acid-Induced Unfolding

We investigate the hydration state of horse-heart cytochrome c (hh cyt c) in the unfolding process induced by trifluoroacetic acid (TFA). The conformation of hh cyt c changes from the native (N) state (2.9 < pH < 6.0) to the acid-unfolded (UA) state (1.7 < pH < 2.0) to the acid-induced molten globule (A) state (pH ∼1.2). Hydration properties of hh cyt c during this process are measured at 20°C by high-resolution dielectric relaxation (DR) spectroscopy, UV-vis absorbance, and circular dichroism spectroscopy. Constrained water of hh cyt c is observed at every pH as an ∼5-GHz Debye component (DC) (DR time, τD ∼30 ps) and its DR amplitude (DRA) is increased by 77% upon N-to-UA transition, when pH changes from 6.0 to 2.0. Even in the N state, the DRA of the constrained-water component is found to be increased by 22% with decreasing pH from 6.0 to 2.9, suggesting an increase in the accessible surface area of native hh cyt c. Moreover, hypermobile water around native hh cyt c is detected at pH 6.0 as a 19-GHz DC (τD ∼ 8.4 ps <τDW = 9.4 ps), but is not found at other pH values. The DRA signal of constrained water is found to return to the pH 2.9 (N-state) level upon UA-to-A transition. Fast-response water (slightly slower than bulk) around A-state hh cyt c is detected at pH 1.2, and this suggests some accumulation of TFA− ions around the peptide chain. Thus, this high-resolution DR spectroscopy study reveals that hh cyt c exhibits significant hydration-state change in the TFA-unfolding process.

Molecular dynamics study of fast dielectric relaxation of water around a molecular-sized ion

We have calculated the dielectric relaxation of water around an ion using molecular dynamics simulations. The collective motion of water near the ion showed fast relaxation, whereas the reorientational motion of individual water molecules does not have the fast component. The ratio of the relaxation time for the fast component and the bulk water was consistent with the experimental results, known as hyper-mobile water, for alkali halide aqueous solution.

Role of Water in Actin–Myosin Binding and Actin Polymerization: Rotational and Translational Mobility of Water Molecules

This paper introduces recent studies on the rotational mobility, translational water diffusion coefficient, and the local viscosity of water around actin filaments (F-actin, a polymerized form of G-actin). Microwave dielectric relaxation spectroscopy (DRS), pulsed-field-gradient spin-echo (PFGSE) proton NMR, and time-resolved fluorescence spectroscopy were employed. The DRS measurements showed that F-actin exhibits dual hydration properties as a structure-maker and a structure-breaker. Thus, in addition to the water molecules with lowered rotational mobility that form a constrained hydration shell around the F-actin, there exist water molecules with rotational relaxation frequencies higher than those of bulk water, which are here referred to as hyper-mobile water. Upon binding of myosin to F-actin, which is an endothermic reaction, the amount of hyper-mobile water increased. A PFGSE NMR study indicated that the water molecules around F-actin have self-diffusion coefficients higher than those around G-actin and in bulk water. The local viscosity of water around actin was also investigated by fluorescence measurements of cyanine dye, Cy3, conjugated to Cys 374 of actin. The estimated rotational correlation time of Cy3 attached to F-actin was 60% lower than that to G-actin, supporting the existence of lower viscosity water around F-actin than that around G-actin. Thus, these three measurements revealed the existence of highly mobile water around F-actin. This could be a clue to understanding the endothermic reactions of myosin/F-actin binding and actin polymerization and constructing the energetics of adenosine-triphosphate-driven protein functions.

2H1424 アクチン周りのハイパーモバイル水の形成とその熱力学的考察(筋肉,口頭発表,日本生物物理学会第50回年会(2012年度))

2H1424 アクチン周りのハイパーモバイル水の形成とその熱力学的考察(筋肉,口頭発表,日本生物物理学会第50回年会(2012年度))

Hydration properties of adenosine phosphate series as studied by microwave dielectric spectroscopy

Hydration properties of adenine nucleotides and orthophosphate (Pi) in aqueous solutions adjusted to pH = 8 with NaOH were studied by high-resolution microwave dielectric relaxation (DR) spectroscopy at 20 °C. The dielectric spectra were analyzed using a mixture theory combined with a least-squares Debye decomposition method. Solutions of Pi and adenine nucleotides showed qualitatively similar dielectric properties described by two Debye components. One component was characterized by a relaxation frequency ( f c = 18.8–19.7 GHz) significantly higher than that of bulk water (17 GHz) and the other by a much lower f c (6.4–7.6 GHz), which are referred to here as hyper-mobile water and constrained water, respectively. By contrast, a hydration shell of only the latter type was found for adenosine ( f c ~ 6.7 GHz). The present results indicate that phosphoryl groups are mostly responsible for affecting the structure of the water surrounding the adenine nucleotides by forming one constrained water layer and an additional three or four layers of hyper-mobile water.

Hydration Analysis on Atp Hydrolysis by Microwave Dielectric Spectroscopy

Recent theoretical works reveiled that the hydration energies of nucleotides and inporganic phosphates are one of important factors in the ATP hydrolysis energy. Here we have measured the hydration states of the reactants and the products of ATP hydrolysis reaction by precesion microwave dielectric relaxation spectroscopy. The complex dielectric spectra of hydrated solutes, such as sodium salts of ATP4-, ADP3- , HPO42-, were measured. We detected constrained water and hyper-mobile water around nucleotides and phosphates. Hydration change upon the neutralization reaction of phosphate, H2PO4- + OH- ◊ HPO42- + H2O, was investigated by measuring high-resolution complex dielectric spectra of mono- and di-sodium phosphate solutions at 20°C to understand the hydration effect on the thermodynamics of phosphate buffer reaction. From each solution spectrum the dielectric spectrum of a spherical volume containing each hydrated solute in water was derived based on a suspension theory. Each spectrum was decomposed into a bulk water (fcw ∼ 17 GHz) component and two Debye dispersion components, assigned as constrained water (fc2 ∼ 6.4GHz fcw), respectively. The dielectric dispersion of hyper-mobile water was about five times stronger than the constrained one. The strengths of these two Debye dispersions decreased by 20% (ΔN2 = −7) for the constrained water number and by 10% (ΔN1 = −15) for the hyper-mobile water number upon the neutralization reaction, while those decrements were compensated by an increase of dispersion strength of bulk water. It is thought that the entropy changes corresponding to the number increases of constrained water and hyper-mobile water molecules are negative and positive, respectively. So the present result provides us a physical explanation of the small effect of hydration change on the total entropy change upon the reaction.

Hyper-Mobile Water around Ions, Charged Polymers, and Proteins Observed with High Resolution Microwave Dielectric Spectroscopy

Hyper-Mobile Water around Ions, Charged Polymers, and Proteins Observed with High Resolution Microwave Dielectric Spectroscopy

A statistical-mechanical analysis on the hypermobile water around a large solute with high surface charge density

In connection with the experimental observation that the hypermobile water is induced around F-actin, we calculate physically insightful components of the rotational entropy of hydration of a solute using the angle-dependent integral equation theory combined with the multipolar model for water. It is shown that when a sufficiently large nonpolar solute is inserted into water, the rotational freedom (RF) of water molecules near the solute is significantly restricted due to the water structuring. When the solute has a moderate surface charge density (SCD), in the region adjacent to the solute and in the region within which the solute-water surface separations are close to the molecular diameter of water, the RF of water molecules becomes considerably higher than in the bulk. As the SCD increases, these regions shift slightly more outside with further enhancement of the RF. For sufficiently high SCD, the water molecules in contact with the solute turn largely restrained. It is shown that the appearance of water molecules with anomalously high RF is the most remarkable for a very large solute with high SCD. We argue that the theoretical results are in qualitatively good accord with the experimental observations for the rotational mobility of water molecules near nonpolar side chains of amino acids and F-actin with the domains which are rich in negative charges.

Theoretical Analysis on Hyper-mobile Water Around a Solute

We calculate physically insightful components of the rotational entropy of hydration of a solute using the angle-dependent integral equation theory combined with the multipolar model for water. It is shown that when a sufficiently large nonpolar solute is inserted into water, the rotational freedom (RF) of water molecules near the solute is significantly restricted due to the water structuring. When the solute has a moderate surface charge density (SCD), in the region next to the solute and in the region within which the solute-water surface separations are close to the molecular diameter of water, the RF of water molecules becomes higher than in the bulk. As the SCD increases, these regions shift slightly more outside with further enhancement of the RF, but the water molecules in contact with the solute turn largely restrained. It is shown that the appearance of water molecules with anomalously high RF is the most remarkable for a very large solute with high SCD like F-actin.

1P-110 高分子電解質ハイドロゲルの膨潤に及ぼすハイパーモバイル水の効果(水・水和/電解質,第47回日本生物物理学会年会)

1P-110 高分子電解質ハイドロゲルの膨潤に及ぼすハイパーモバイル水の効果(水・水和/電解質,第47回日本生物物理学会年会)

3P-115 溶質近傍のハイパーモバイル水に関する理論解析(水・水和/電解質,第46回日本生物物理学会年会)

3P-115 溶質近傍のハイパーモバイル水に関する理論解析(水・水和/電解質,第46回日本生物物理学会年会)

Rotational Mobility of Water around Muscle Proteins by High-Resolution Microwave Dielectric Spectroscopy and a Clue to Molecular Mechanism of Muscle Contraction

A precision microwave dielectric spectroscopic technique has been developed. This technique enables us to analyze hydration properties of ions, proteins, and other biomolecules. φ-scan method gives an image of the information of spatial distribution of dielectric property of water surrounding protein molecules. Fixed φ analysis gives a direct comparison of hydration properties of different proteins. With this technique we analyzed the state change of F-actin hydration upon binding with myosin, and found that hyper-mobile water (HMW) is induced around F-actin and increased upon binding with myosin S1. Thus, we may obtain further information of collective properties of water surrounding proteins and biomolecules.

1P156 ハイパーモバイル水の証拠 : F-actin水溶液中のプロトン拡散系数は純水より大きくmyosin-S1結合でさらに増大(筋肉(筋蛋白質・収縮),口頭発表,第45回日本生物物理学会年会)

1P156 ハイパーモバイル水の証拠 : F-actin水溶液中のプロトン拡散系数は純水より大きくmyosin-S1結合でさらに増大(筋肉(筋蛋白質・収縮),口頭発表,第45回日本生物物理学会年会)