Membrane protein crystallization in lipidic mesophases with tailored bilayers.

Monoacylglycerols have been used as bilayered hosts for growing crystals of membrane proteins. To date, the lipids used have had chains 16 and 18 carbon atoms long. We hypothesized that a shorter-chained lipid producing a thinner bilayer would facilitate the so-called in meso crystallization process. A 14 carbon monoacylglycerol was chosen as the lipid with which to test the proposal. To be compatible with the in meso method, a cis olefinic bond was placed in its acyl chain at a location arrived at by rational design. The target lipid was synthesized and was shown to form the requisite mesophase at room temperature. In support of the hypothesis, it produced crystals of bacteriorhodopsin and the outer membrane transporter, BtuB. The latter is the first beta barrel protein to be crystallized by the in meso method. Protein stability in the short-chain lipid and how this relates to crystallogenesis are discussed.