Crystallizing Membrane Proteins for Structure Determination: Use of Lipidic Mesophases

The principal route to determine the structure and the function and interactions of membrane proteins is via macromolecular crystallography. For macromolecular crystallography to be successful, structure-quality crystals of the target protein must be forthcoming, and crystallogenesis represents a major challenge. Several techniques are employed to crystallize membrane proteins, and the bulk of these techniques make direct use of solubilized protein-surfactant complexes by the more traditional, so-called in surfo methods. An alternative in meso approach, which employs a bicontinuous lipidic mesophase, has emerged as a method with considerable promise in part because it involves reconstitution of the solubilized protein back into a stabilizing and organizing lipid bilayer reservoir as a prelude to crystallogenesis. A hypothesis for how the method works at the molecular level and experimental evidence in support of the proposal are reviewed here. The latest advances, successes, and challenges associated with the method are described.