Quasi-Laue neu iron-diffraction study of the water arrangement in crystalsof triclinic hen egg-white lysozyme

Triclinic crystals of lysozyme, hydrogen-deuterium exchanged in deuterated solvent, have been studied using neutron quasi-Laue techniques and a newly developed cylinder image-plate detector. The wavelength range employed was from 2.7 to 3.5 Angstrom, which gave 9426 significant reflections [F greate r than or equal to 2 sigma(F)] to a resolution limit of 1.7 Angstrom. The d euteration states of the H atoms in the protein molecule were identified, f ollowed by an extensive analysis of the water structure surrounding the pro tein. The final R factor was 20.4% (R-free = 22.1%). In total, the 244 obse rved water molecules form approximately one layer of water around the prote in with far fewer water molecules located further away. Water molecules cov ering the apolar patches make tangential layers at 4-5 Angstrom from the su rface or form C-H ... O contacts, and several water-molecule sites can be i dentified in the apolar cavities. Many of the water molecules are apparentl y orientationally disordered, and only 115 out of the 244 water molecules s it in mean single orientations. Comparison of these results with quasi-elas tic neutron scattering observations of the water dynamics leads to a pictur e of the water molecules forming an extended constantly fluctuating network covering the protein surface.