ABSTRACT
There is one report about the crystallization of a membrane-anchored protein. However, the crystals of the hydrophilic domain alone, which could also be obtained, are of a much better quality. This chapter discusses purity, homogeneity, and stability of membrane proteins are the most important prerequisites for their crystallization. The most suited starting materials for membrane protein isolation are specialized biological membranes, where certain membrane proteins are considerably enriched. One of the worst obstacles in membrane protein crystallization is the detergent's tendency to form a separate, viscous detergent phase. This detergent phase is formed upon the addition of precipitants and/or temperature shifts and contains the membrane proteins. Normally membrane proteins are isolated using a rather mild, inexpensive detergent like Triton X-100 which is not suited for the crystallization. The membrane protein is then eluted with the new detergent by increasing the ionic strength or by changing the pH. During crystallization attempts the membrane protein can undergo several competing reactions.
