9.8 MAG: A New Host Lipid for In Meso (Lipid Cubic Phase) Crystallization of Integral Membrane Proteins

Monoolein, also referred to as 9.9 MAG, is the most commonly used monoacylglycerol for crystallizing membrane proteins by the in meso method. However, 9.9 MAG does not work for all proteins. Therefore, having available a suite of monoacylglycerols, the members of which differ in acyl chain characteristics such as chain length and position along the chain of the cis-olefinic bond, is an important screening feature. Several monoacylglycerols of this type are available and have proven their worth in enabling the structure determination of high-profile targets, including the β₂-adrenoreceptor-Gs protein and the rhodopsin-arrestin complexes, and cytochrome caa₃ oxidase. Here a new monoacylglycerol, 9.8 MAG, is introduced. Since the performance in crystallogenesis depends critically on the phase properties of the host lipid, the thermotropic and lyotropic mesophase behavior and microstructure of hydrated 9.8 MAG have been quantified by small-angle X-ray diffraction. The lipid is shown to be compatible with cholesterol at levels typically used in crystallization trials. Further, 9.8 MAG supports the crystallization and structure determination of two benchmark proteins: the α-helical lipoprotein N-acyltransferase, Lnt, and the β-barrel alginate transporter, AlgE. 9.8 MAG can now be included in host lipid screens to optimize the structure determination of a broader range of membrane proteins, many of which are scientifically and medically important.