X-ray scattering study of the structure of water around myoglobin for several levels of hydration

Water has been shown to play a crucial role in the stability and catalytic function of protein. Our purpose is to understand the modification of bulk liquid behavior when water is around myoglobin, in particular, the perturbation of liquid water structure by hydrophobic and hydrophilic sites of the protein. For this, the structure of water adsorbed at two different surfaces of a hydrophobic medium such as activated charcoal and a hydrophilic one such as polyHEMA (a synthetic hydrogel) was studied using both x-ray and neutron scattering techniques in earlier works. Following this study, the structure of water around myoglobin is investigated by x-ray scattering at room temperature and down to 77 K. The structure factors and the corresponding radial distribution functions are determined for several levels of hydration. At high water content (3 g water/g protein) the properties of water are very similar to those of bulk water. In partially hydrated samples (<0.4 g water/g protein), the molecular structure of water determined by water-water radial distribution function exhibits significant change, especially in the range of 3.3<r<3.9 A. These changes correspond to a distortion of the hydrogen-bonded network at the level of the first and second neighbors, and water does not crystallize when the temperature is lowered. (C) 2002 American Institute of Physics.