Macromolecular crystallography

X-ray crystallography is used to determine the three-dimensional atomic-resolution structure of a molecule by measuring how an ordered crystal diffracts X-rays. It remains the highest-resolution, most established method for visualizing exactly how atoms are arranged — including precisely how ligands and drugs bind. The path from purified protein to deposited structure runs through several distinct stages, each with its own requirements.

Sample Requirements

• General: Highly pure (>95%), homogeneous, monodisperse protein, usually concentrated to 5 – 20 mg/mL. Milligram quantities are typically needed to complete screening and optimization.
• Crystallization screening: Few hundreds of microliters of a macromolecular solution (as above) to set up hundreds of conditions in nanoliter drops.
• Co-crystallization / soaking: Ligand at high purity and solubility, ideally in aqueous solution, but some organic solvents can be tolerated; for soaking, pre-grown apo crystals plus concentrated ligand stock.
• Buffer constraints: As minimal as possible. Low amounts of buffers with low-ionic-strength (limited salt) are often preferred. Remove glycerol and additives if possible.