Importance of Hydration State around Proteins Required to Grow High-Quality Protein Crystals

The explosive increase in the normal growth rates for dislocation free tetragonal hen egg white (HEW) lysozyme crystals was observed from the point of (C - C_eq), corresponding to a high supersaturation ratio of 2.2. This suggests that the change in the growth mode, i.e., the normal growth rates, is dominated not by the surface free energy of the step edge, but by the dynamics of water around protein molecules under high supersaturation ratios. Focusing on the crystal quality at high supersaturation conditions, the quality improvement for protein crystals was also observed with an increase in water dynamics around protein molecules, despite the faster normal growth rate, as verified by the full width at half-maximum values (FWHMs) of X-ray diffraction (XRD) rocking curves. Moreover, the misorientation between subgrains reached the order of 10^-4° for tetragonal HEW lysozyme crystals grown with the NaCl concentration of 0.86 M, and thus bead-like contrasts of dislocation explained by the dynamical theory of diffraction were also observed using X-ray topography conducted with a beam of monochromatic synchrotron radiation. This indicates that the grown tetragonal HEW lysozyme crystal has near-perfect quality and changes the traditional concept that high-quality protein crystals are obtained by low normal crystal growth rates. Here we show the importance of the hydration state around protein molecules required to grow high-quality protein crystals.