Crystallization of Proteins

Protein crystals are needed for solving their three dimensional structure. Proteins can be crystallized using vapor diffusion, where crystals grow from a supersaturated protein-containing drop. The protein concentration is slowly increased by equilibration against a reservoir containing a precipitating agent. It can be a time consuming task to obtain crystals of a quality that diffract the X-ray well enough to obtain a crystal structure

Hanging-drop crystallization: protein-containing
drops equilibrate against a reservoir

Due to high diversity among different proteins the optimal crystallization conditions are very different.  Searching the optimal conditions many factors (e.g. temperature, pH and concentrations) are varied using the trial-and-error principle.

Examples of drops with protein crystals: D14C [4Fe-4S]
Pyrococcus furiosus Ferredoxin