Protein crystallization

Protein crystallization is the process of formation of a protein crystal. While some protein crystals have been observed in nature, protein crystallization is predominantly used for scientific or industrial purposes, most notably for study by X-ray crystallography. Like many other types of molecules, proteins can be prompted to form crystals when the solution in which they are dissolved becomes supersaturated. Under these conditions, individual protein molecules can pack in a repeating array, held together by noncovalent interactions. These crystals can then be used in structural biology to study the molecular structure of the protein, or for various industrial or biotechnological purposes.

Proteins are biological macromolecules and function in an aqueous environment, so protein crystallization is predominantly carried out in water. Protein crystallization is generally considered challenging due to the restrictions of the aqueous environment, difficulties in obtaining high-quality protein samples, as well as sensitivity of protein samples to temperature, pH, ionic strength, and other factors. Proteins vary greatly in their physicochemical characteristics, and so crystallization of a particular protein is rarely predictable. Determination of appropriate crystallization conditions for a given protein often requires empirical testing of many conditions before a successful crystallization condition is found.

Crystallization of protein molecules has been known for over 150 years.

In 1934, John Desmond Bernal and his student Dorothy Hodgkin discovered that protein crystals surrounded by their mother liquor gave better diffraction patterns than dried crystals. Using pepsin, they were the first to discern the diffraction pattern of a wet, globular protein. Prior to Bernal and Hodgkin, protein crystallography had only been performed in dry conditions with inconsistent and unreliable results.

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