Practical Physics Behind Growing Crystals of Biological Macromolecules

The aim of this review is to provide biocrystallographers who intend to tackle protein-crystallization with the- ory and practical examples. Crystallization involves two separate processes, nucleation and growth, which are rarely com- pletely unconnected. Here we give theoretical background and concrete examples illustrating protein crystallization. We describe the nucleation of a new phase, solid or liquid, and the growth and transformation of existing crystals obtained by primary or secondary nucleation or by seeding. Above all, we believe that a thorough knowledge of the phase diagram is vital to the selection of starting position and path for any crystallization experiment.