Isoprenoid-chained lipid β-XylOC16+4—A novel molecule for in meso membrane protein crystallization

Here we report a successful use of a recently developed isoprenoid-chained lipid family for in meso crystallization of membrane proteins. The isoprenoid-chained lipid 1-O-(3,7,11,15-tetramethylhexadecyl)-β–d-xyloside (β-XylOC16+4) used as a host lipid for in meso crystallization provided high quality bacteriorhodopsin (bR) crystals (P63 space group) diffracting to high resolution and characterized by low twinning ratio. β-XylOC16+4 has an isoprenoid chain with methyl branches at each 4th position and a xylose group in the water-soluble part. These peculiarities make the lipid clearly distinguishable in the bR crystalline lattice and provides a unique opportunity to study the role of the host lipid in the in meso crystallization. We conclude that β-XylOC16+4 may have a general application for in meso crystallization for a wide range of membrane proteins. The cubic phase of β-XylOC16+4 is present over a wide range of temperatures and is stable at low temperature (down to about 8 °C). This opens up the possibility of using temperature as a tool for the optimization of in meso crystallization with additional advantages for the crystallization of membrane proteins at lower temperatures where the proteins of interest may be more stable.