Lipidic cubic phase (LCP) is one of many liquid crystalline phases that form spontaneously upon mixing lipids with water at proper conditions (Fig 1). Structuraly LCP consists of a single lipid bilayer that follows an infinite periodic minimal surface (IPMS) dividing the space into two non-intersecting networks of water channels. There are three common types of bicontinuous LCPs with different space group symmetry (Fig. 2). LCP possesses many unique properties (Box 1), making it an attractive tool for a number of applications (Box 2). Crystallization of membrane proteins in LCP was introduced in 1996 by Landau & Rosenbusch (1). This technique has proven to be crucial for elucidating structural mechanisms of action of several microbial rhodopsins, as well as provided the first high-resolution details of human G protein-coupled receptors (GPCR) bound to diffusible ligands. Success of using LCP for growing highly ordered crystals of challenging human membrane proteins can be attributed to at least two factors. LCP provides a more native-like membrane environment for proteins as opposed to a rather harsh environment associated with detergent micelles. Crystals grown in LCP have type I packing with protein molecules making contacts not only through hydrophilic but also through hydrophobic portions resulting in lower solvent content and better crystal ordering (Fig. 3). Click here >> to see the stats on membrane protein structures crystallized in LCP.
1. Landau, E.M., and J.P. Rosenbusch. (1996) Lipidic cubic phases: a novel concept for the crystallization of membrane proteins. Proc. Natl. Acad. Sci. U S A 93: 14532-14535. >>
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