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TRANSMEMBRANE PROTEIN CRYSTALLIZATION

One of the goals for the Center for High-Throughput Structural Biology is to develop crystallization screens specifically tailored to membrane proteins.  This class of proteins presents a greater challenge, since they require a detergent solubilization step to remove the protein from the lipid bilayer to form a stable, homogeneous protein-detergent complex (PDC)1.  Crystallization of the subsequent PDC requires the manipulation of the dual surface properties of the PDC in the presence of various precipitants.  As membrane proteins have been observed to form crystals close to the phase boundaries of the detergent used in the crystallization experiment, knowledge of these boundaries under different precipitant conditions can serve as the foundation for the design of optimal crystallization screens for membrane proteins1,2.  Our initial experiments consist of characterizing the phase separation boundaries of pure detergents in the presence of various crystallization precipitants using dye-partitioning experiments (Fig. 1).  Information obtained from these studies will be used as the basis for enhancing our screening solutions with the introduction of detergent-specific cocktails designed to approach the phase boundary of the particular detergent used in the PDC.  The TMPs, which are purified in several different detergents, can then be screened against a specific set of 384 cocktail solutions that have been formulated using a matrix of detergents, salts, and polyethylene glycols (Fig. 2). This intelligent crystallization screen for membrane proteins will be used in conjunction with the 1536-well plate high-throughput crystallization robots located at the Hauptman-Woodward Institute.

References

1Loll, P.J. (2003) Membrane protein structural biology: the high-throughput challenge.  J. Structural Biol. 142, 144-153.
[PubMed]

2Weiner, M.C. and Snook, C.F. (2001) The development of membrane protein crystallization screens based upon detergent solution properties.  J. Cryst. Growth 232, 426-431.