Crystallizing membrane proteins for structure-function studies using lipidic mesophases

Abstract

The lipidic cubic mesophase or in meso method for crystallizing membrane proteins has posted some high profile successes recently. This is especially true in the area of G protein-coupled receptors with over a dozen new crystallographic structures emerging in the past 5years. Slowly, it is becoming an accepted method with a proven record and convincing generality. However, it is not a method that is used in every membrane structural biology laboratory and that is unfortunate. The reluctance in adopting it is attributable, in part, to the anticipated difficulties associated with handling the sticky, viscous cubic mesophase in which crystals grow. Harvesting and collecting diffraction data with the mesophase-grown crystals is also viewed with some trepidation. It is acknowledged that there are challenges associated with the method. However, over the years we have worked to make the method user-friendly. To this end, tools for handling the mesophase in the pico- to nanolitre volume range have been developed for efficient crystallization screening in manual and robotic modes. Glass crystallization plates have been built that provide unparalleled optical quality and sensitivity to nascent crystals. Lipid and precipitant screens have been implemented for a more rational approach to crystallogenesis such that the method can now be applied to a wide variety of membrane protein types and sizes. These assorted advances are outlined here along with a summary of the membrane proteins that have yielded to the method. The challenges that must be overcome to further develop the method are described. © 2013 Springer Science+Business Media Dordrecht.