2. Purification of biological macromolecules

Obtaining quality crystals usually requires several milligrams of the macromolecule of interest in a soluble state and of very high purity. The first three-dimensional structures of macromolecules corresponded to molecules that could easily be obtained in large quantities and crystallized relatively easily. Today, the crystallographic study of a macromolecule is used to solve a specific biological problem. The target macromolecule may be available in small quantities, or even be practically insoluble. Nevertheless, the significant growth in the number of three-dimensional structures solved is due to the use of molecular biology techniques. Once the gene corresponding to the protein under investigation has been identified, it can be cloned into an expression vector and expressed in a prokaryotic or eukaryotic host cell. The overexpression systems most commonly used for structural studies...