Spatiotemporal development of soaked protein crystal

Crystal soaking is widely performed in biological crystallography. This paper reports time-resolved X-ray crystallographic and microtomographic analyses of tetragonal crystals of chicken egg-white lysozyme soaked in mother liquor containing potassium hexachloroplatinate. The microtomographic analysis showed that X-ray attenuation spread from the superficial layer of the crystal and then to the crystal core. The crystallographic analyses indicated that platinum sites can be classified into two groups from the temporal development of the electron densities. A soaking process consisting of binding-rate-driven and equilibrium-driven layers is proposed to describe these results. This study suggests that the composition of chemical and structural species resulting from the soaking process varies depending on the position in the crystal.