This rapid progress can be attributed in part to the growing number of tools available to structural biologists: crystallization robots, a wide range of commercially available detergents, and protein from recombinant sources ( Drew et al. The last 10 years have seen a dramatic increase in the number of high-resolution membrane protein structures ( Berman et al. The implications of our results for membrane protein crystallization prescreening are discussed. Here we use the UDS method in the identification of suitable detergents and buffer compositions for the crystallization of three recombinant prokaryotic membrane proteins. In addition, the UDS method allows rapid screening of detergents for membrane protein crystallization in a fraction of the time required by SEC. The results from the UDS method correlate very well with established methods like size-exclusion chromatography (SEC), while consuming considerably less protein. Here we describe a novel ultracentrifugation dispersity sedimentation (UDS) assay in which ultracentrifugation of very small (5 μL) volumes of purified, soluble membrane protein is combined with SDS-PAGE analysis to rapidly assess the degree of protein aggregation. The optimization of these parameters is often a time- and protein-consuming process. Critical buffer components affecting the aggregation of membrane proteins include detergent choice, salt concentration, and presence of glycerol. This nonspecific aggregation of the molecules reduces the likelihood of the regular association of the protein molecules essential for crystal lattice formation.
Because of their hydrophobic nature, membrane proteins are particularly prone to forming insoluble aggregates over time. One key to successful crystallization of membrane proteins is the identification of detergents that maintain the protein in a soluble, monodispersed state.
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