Contrasting Changes in Strongly and Weakly Bound Hydration Water of a Protein upon Denaturation

Abstract

Water is considered integral for the stabilization and function of proteins, which has recently attracted significant attention. However, the microscopic aspects of water ranging up to the second hydration shell, including strongly and weakly bound water at the sub-nanometer scale, are not yet well understood. Here, we combined terahertz spectroscopy, thermal measurements, and infrared spectroscopy to clarify how the strongly and weakly bound hydration water changes upon protein denaturation. With denaturation, that is, the exposure of hydrophobic groups in water and entanglement of hydrophilic groups, the number of strongly bound hydration water decreased, while the number of weakly bound hydration water increased. Even though the constraint of water due to hydrophobic hydration is weak, it extends to the second hydration shell as it is caused by the strengthening of hydrogen bonds between water molecules, which is likely the key microscopic mechanism for the destabilization of the native state due to hydration.

Measurement of Water Uptake and States in Nafion Membranes Using Humidity-Controlled Terahertz Time-Domain Spectroscopy

“…This collective relaxation, however, is not Raman active as opposed to free water, which could be, with origins from the collisional relaxation inside the nonhydrogen bonding structure . The remaining water population according to eq is assigned as bound water, which has been shown to contain both strongly and loosely bound water in solutions . DSC nonfreezable water is generally associated with strongly bound water, , but this was shown to be higher than the total bound water determined from our terahertz data, indicating inconsistency between these measurements.…”

Efficient design and synthesis of an amorphous conjugated polymer network for a metal-free electrocatalyst of hydrogen evolution reaction

“…THz-TDS is used to analyze the hydration state, including water weakly affected by solutes, and the method is applied to study the hydration behavior of macromolecules and small molecules. 73–84 In the THz frequency band, the collective rotational relaxation dynamics of water (slow relaxation), dynamics of water isolated from hydrogen bonds (fast relaxation), and stretching vibrations between water molecules exist. 85–87 Hydration amounts were obtained with the same method in the literature.…”

“…85–87 Hydration amounts were obtained with the same method in the literature. 75,77,81,82 When water is bound to a solute, the slow relaxation becomes slower than the bulk water, and the intensity of the slow relaxation of the bulk water is reduced by the decrease in the amount of bulk water. Primarily, the amount of hydration water can be quantified from this decrease in bulk water.…”

“…The spectrum shown in Fig. 8g was fitted with the following eqn (2), 75–77 and obtained parameters were used to calculate the amount of hydration, n , from eqn (3). 74 Because of the accuracy of the measurement, only the imaginary part was used in the analysis.Δ ε slow and Δ ε fast are the strengths of the slow and fast relaxations, and τ slow and τ fast are their respective relaxation times.…”

Osmolyte induced protein stabilization: modulation of associated water dynamics might be a key factor

“…19,21,39,72 However, there is a limited number of papers that concurrently assess and compare the modulation of water structure and the stability of the protein. 27,81,82 The most comprehensive report came very recently, where the authors examined the water structure modulation with 20 osmolytes and compared that to the stability of ribonuclease-A. 27 They found a definitive, but not so very strong correlation between water structure modulation and protein stability.…”