Abstract
The initial stage of crystallization, often called nucleation, is critically important for the eventual size, property and perfection of crystals. For protein crystals used in structure determination by X-ray crystallography, the understanding and control of nucleation are particularly required. Based on the large ratio of the molecular size of proteins and the distance over which the attractive interaction is extended, liquid-liquid metastable coexistence curve can be situated near the solution-crystalline solubility curve. By use of the liquid-liquid phase separation, nucleation can be promoted or controlled. Three papers (ten Wolde and Frenkel, Costa et al., and Drenth and Haas) are introduced and explained. Experimental works of the author's group using transmission electron microscopy and dynamic light scattering are then explained. The former detected formation of spherical structures (15 nm in diameter) in solutions of 10, 15, and 30 mg/ml hen egg-white lysozyme at 10, 4 and 2 h after supersaturation, respectively, at 20℃, 5% (w/v) NaCl and pH 4.6. The latter showed the advantages of using polyethylene glycol as a crystallizing agent in controlling the position of the liquid-liquid coexistence curve in relation to the solution-crystalline solubility curve.
