Properties of Hydration Shells of Protein Molecules at their Pressure- and Temperature-Induced Native-Denatured Transition

Understanding the function of water during the gelation of globular proteins by temperature-dependent near infrared spectroscopy

Water plays an indispensable role in the gelation of proteins, but its function still remains unclear. In this work, the variation of water species with the structural changes of globular proteins was investigated using temperature-dependent near infrared (NIR) spectroscopy. Ovalbumin (OVA) was used as a model protein, which forms a gel-like structure as the temperature increases through three phases, i.e., phase I (native), phase II (molten globule state), and phase III (gel state). The structural change and the content variation of different water species in the three phases of gelation were analyzed by two-dimensional correlation NIR spectroscopy and Gaussian fitting. A decrease in the water species with two hydrogen bonds (S2) was found and the change follows the same phases as OVA. In the first two phases, the change occurs after those of other water species but in the third phase, the change is faster than that of free water species. The result indicates that in the native and molten globule states, S2 is located in the hydration shell of OVA to maintain the stability of the protein structure, and then in the gel state, high temperature weakens the hydrogen bonding of S2 and leads to the destruction of the hydration shell, making OVA clusters form a gel structure.

Link between the hydration enthalpy of lysozyme and the density of its hydration water: Electrostriction

Hydration shells around proteins in solution are on average denser than bulk water. Variations in enthalpy are observed during hydration/dehydration of proteins. To explain consistently those phenomena, a common mechanism-electrostriction-underlying the mechanical and contributing to thermal effects is proposed. The mean mass density of the hydration shell of lysozyme derived from the neutron and X-ray scattering is explained as following the compression of water in the fields of the order of 10(9) V m(-1) due to the charged sites at the boundary of the protein. The mean enthalpy of mixing ΔH(mean) of lysozyme in water calculated on the basis of the measured mean mass density falls in the middle of the values of the enthalpy of mixing ΔH(mix) observed in sorption experiments. This testifies that ΔH(mix) is due in part to the work done by the electrostriction pressure in hydration shell regions situated in high electric fields. The dependence of the sorption enthalpy of exemplary proteins on the number of adsorbed H(2)O molecules is also described in terms of electrostriction.