Proteins, fragment cocrystallization

Generating suitable protein is often the most labor intensive step on the way to 3D structures. Enough protein to create hundreds of crystals is needed and therefore care needs to be taken with expression and purification procedures. High yield expression and simple and effective purification protocols are beneficial. Optimized protein constructs for crystallization often lack glycosylation sites and carry affinity tags for purification. All standard structural biology protein expression systems are used to produce the proteins for fragment cocrystallization, i.e., E. coli, Baculo virus insect cell systems or mammalian cell lines. 

In addition to the influence of the detergent on crystallization, the introduction of additional protein components has proven to be successful. In several cases, an antibody fragment was cocrystallized with the membrane protein to provide essential crystal contacts for crystallization (55-57). The protein itself can be engineered with an insertion to provide crystal contacts as demonstrated by the recent success of human 32 adrenergic G-protein-coupled receptor stmcture, in which a lysozyme molecule was engineered into one of the loops (58). 

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