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The lipidic cubic phase (LCP) has been widely recognized as a promising membrane-mimicking matrix for biophysical studies of membrane proteins and their crystallization in a lipidic environment. Application of this material to a wide variety of membrane proteins, however, is hindered due to a limited number of available host lipids, mostly monoacylglycerols (MAGs). Here, we designed, synthesized, and characterized a series of chemically stable lipids resistant to hydrolysis, with properties complementary to the widely used MAGs. In order to assess their potential to serve as host lipids for crystallization, we characterized the phase properties and lattice parameters of mesophases made of two most promising lipids at a variety of different conditions by polarized light microscopy and small-angle X-ray scattering. Both lipids showed remarkable chemical stability and an extended LCP region in the phase diagram covering a wide range of temperatures down to 4 °C. One of these lipids has been used for crystallization and structure determination of a prototypical membrane protein bacteriorhodopsin at 4 and 20 °C. [ABSTRACT FROM AUTHOR]

Since the introduction of in meso crystallization of membrane proteins in lipidic cubic phase (LCP) by Landau and Rosenbusch in 1996, numerous studies attempted to elucidate the mechanism of in meso crystal nucleation and growth. Here we present a fluorescence microscopy study of the crystallization process of the light-driven proton pump bacteriorhodopsin. The crystallization starts with formation of microcrystals, followed by growth of a dominating crystal at the expense of smaller ones and formation of a depletion zone around it. These observations suggest an Ostwald ripening mechanism of the in meso crystal growth. Analysis of the microcrystal spatial distribution suggests that microcrystal nucleation occurs predominately at the LCP domain boundaries. [ABSTRACT FROM AUTHOR]