Bio-Beads: an efficient strategy for two-dimensional crystallization of membrane proteins.

This work establishes the potential of Bio-Beads as a simple alternative to conventional dialysis for removing detergent and for obtaining 2D crystals of integral membrane proteins useful for structure analysis by electron crystallography. Kinetic and equilibrium aspects of removal of different detergents by adsorption onto hydrophobic Bio-Beads SM2 have been systematically investigated and extended to 2D crystallization of different prototypic membrane proteins, including: (a) Ca2+ ATPase from sarcoplasmic reticulum; (b) melibiose permease from Escherichia coli; (c) cytochrome b6f from Chlamydomonas reinhardtii. Different crystals could be produced from all protein preparations, with optical diffraction down to 20-25 A in negative stain.