DYNAMICS OF PROTEIN PRECRYSTALLIZATION CLUSTER FORMATION

In the initial stages of crystallization of hen egg-white lysozyme, monomers aggregate rapidly and form large precrystallization fractal clusters, as shown by photon correlation spectroscopy (PCS). The growth of these clusters resembles closely that of inorganic colloids taking place either in the reaction limited (RLCA), crossover (XOVER), or diffusion limited (DLCA) cluster aggregation regimes [see Lin et al., Colloid Interface Sci. 137 (1990) 263; Phys. Condensed Matter 2 (1990) 3093; and citations therein]. Under supersaturation conditions low quality crystals appear after long incubation periods in the XOVER regime, whereas large, strongly X-ray diffracting crystals are obtained after a few hours from clusters growing in the DLCA regime. We propose that, via observation of parameters such as the growth regime, the limiting size of the clusters and the resulting growth exponents, the fate of a protein solution undergoing crystallization can be predicted and optimized in its very early stages.