Abstract
High-quality crystals are expected to grow in microgravity environment. A protein depletion zone (PDZ) and an impurity depletion zone (IDZ) around a growing crystal are formed in microgravity environment because of the suppressions of convection flow. These depletion zones decrease concentrations of protein and impurities on the surface of the crystal, resulting in high quality crystal growth. Previously, we developed an easy method to estimate the effects of PDZ and IDZ in a steady state by using the combination of the diffusion coefficient and the kinetic constant of the protein molecule and the radius of the crystal, and have successfully applied it to increase microgravity effects on growing high-quality crystals. From this method, we learned that high-quality crystals could grow in microgravity if the crystals were larger, the protein sample was highly purified, and the crystallization solution was viscous. Recently, we introduced a numerical analysis of these depletion zones in a non-steady state and suggested that all the sections of the crystal are surrounded by different supersaturation levels of protein and different concentrations of impurity. Especially for the crystals grown on the ground, the concentration of impurity was higher in the center of the crystals. Our recent experimental results suggested that the cell dimensions of ground-grown crystals of lysozyme with some impurity were not uniform in a crystal. We speculated that it was because the disorder in the center of the crystal grown on the ground affected to the crystal lattice of the outer layer of the crystal. In this review, technical background of protein crystallization in space is reviewed.
