@article{faa01c31dee04e93b95a600bf54cd1cf,
title = "Effects of detergent β-octylglucoside and phosphate salt solutions on phase behavior of monoolein mesophases",
abstract = "Using small-angle x-ray scattering (SAXS), we investigated the phase behavior of mesophases of monoolein (MO) mixed with additives commonly used for the crystallization of membrane proteins from lipidic mesophases. In particular, we examined the effect of sodium and potassium phosphate salts and the detergent β-octylglucoside (βOG) over a wide range of compositions relevant for the crystallization of membrane proteins in lipidic mesophases. We studied two types of systems: 1), ternary mixtures of MO with salt solutions above the hydration boundary; and 2), quaternary mixtures of MO with βOG and salt solutions over a wide range of hydration conditions. All quaternary mixtures showed highly regular lyotropic phase behavior with the same sequence of phases (Lα, Ia3d, and Pn3m) as MO/water mixtures at similar temperatures. The effects of additives in quaternary systems agreed qualitatively with those found in ternary mixtures in which only one additive is present. However, quantitative differences in the effects of additives on the lattice parameters of fully hydrated mesophases were found between ternary and quaternary mixtures. We discuss the implications of these findings for mechanistic investigations of membrane protein crystallization in lipidic mesophases and for studies of the suitability of precipitants for mesophase-based crystallization methods.",
author = "Khvostichenko, {Daria S.} and Ng, {Johnathan J.D.} and Perry, {Sarah L.} and Monisha Menon and Kenis, {Paul J.A.}",
note = "Funding Information: We investigated the phase behavior of MO mesophases mixed with the detergent β OG and sodium or potassium phosphate salts that are frequently used for crystallization of membrane proteins from lipidic mesophases The compositions of mixtures were selected to closely resemble conditions for membrane protein crystallization in lipidic mesophases in meso: β OG/MO and salt/water ratios were kept constant, and the hydration level (the weight fraction of the salt solution in the mixture) in the mixture was varied. We also studied MO mixtures with salt solutions without detergent under conditions of excess aqueous phase. The quaternary MO/ β OG/water/phosphate salt mesophases studied here exhibited a remarkably regular behavior, with a sequence of phases matching that for MO/water mesophases as a function of aqueous solution content. The location of phase boundaries and the values for lattice parameters both above and below the hydration boundary shifted in agreement with previously established effects for detergents and phosphate salts on the microstructure of MO mesophases. The apparent quantitative dependences of lattice parameters of fully hydrated mesophases on the concentration of additives in the quaternary systems differed from estimates based on data for ternary MO/water/additive systems. Hence, it is difficult, if not impossible, to make a priori quantitative predictions of lattice parameters in crystallization mixtures based on simple correlations. Additionally, we found evidence for a redistribution of additives between the mesophase and the aqueous solution, potentially causing significant changes in the compositional makeup of the mesophase, such as the β OG/MO ratio and the salt concentration in the aqueous channels within the mesophase. In summary, our findings strongly suggest that the compatibility of precipitants with the formation of the cubic phase necessary for protein crystallogenesis in lipidic mesophases must be probed under conditions that are directly relevant to crystallization trials, i.e., with detergent present in the mixture and with a large amount of precipitant. The exact amount of precipitant in the mixture may be of particular importance for precipitants containing small molecules that may partition between both the aqueous and lipidic environments. The multitude of detergents and precipitants available, as well as the lack of fine control over the detergent concentrations in protein solutions used for crystallization, make the parameter space enormous. Recent developments ( 62,63 ) in high-throughput SAXS analysis of lipidic mesophases may greatly facilitate such studies. We thank Dr. Elena Kondrashkina, Dr. Keith Brister, and Mr. Jay Von Osinski for the development of the SAXS setup at the APS and assistance in data collection. The assistance of Dr. Danielle Gray and Dr. Amy Fuller was invaluable throughout SAXS data collection and analysis at the X-Ray Diffraction Laboratory, University of Illinois at Urbana-Champaign. Dr. Sudipto Guha and Dr. Ashtamurthy Pawate provided help in SAXS data collection at the APS. We thank Prof. Alexey Victorov for insightful comments on the manuscript. This work was funded by the NIH (R01 GM086727). Use of the Advanced Photon Source was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract No. DE-AC02-06CH11357. Use of the LS-CAT Sector 21 was supported by the Michigan Economic Development Corporation as well as the University of Illinois. ",
year = "2013",
month = oct,
day = "15",
doi = "10.1016/j.bpj.2013.09.009",
language = "English (US)",
volume = "105",
pages = "1848--1859",
journal = "Biophysical journal",
issn = "0006-3495",
publisher = "Elsevier B.V.",
number = "8",
}