Usefulness of oils for cleaning the host matrix and for cryoprotection of lipidic cubic phase crystals

The lipidic cubic phase method is an effective approach for membrane protein crystallography. The in meso grown crystals are usually cryocooled directly without removing the host matrix from the harvested crystal surface. However, the host matrix often causes the appearance of scattering rings and an increase in background scattering during the data collection. Moreover, the frozen host matrix sometimes becomes opaque and it can hinder conventional crystal centering. In this study, several oils were examined for their ability to clean the host matrix and to provide cryoprotection for crystals grown in the lipidic cubic phase. Several of the tested oils appeared to be useful in terms of their effect on crystal stability and background scattering. This method should be of value for the collection of highly accurate data sets.