Ai, X. and Caffrey, M.

OSBP and Department of Chemistry

Because of their mild nature, the alkyl glycosides have found extensive use in solubilizing membrane proteins for subsequent structure characterization, reconstitution and crystallization studies. Dodecyl maltoside (DM) has been used in such applications and is currently being evaluated for its effects on the system used to induce crystallization of membrane proteins in cubo. The latter method uses a multicomponent system where hydrated monoolein in the cubic mesophase figures prominently. While the exact role of the cubic phase in the crystallization process is still a mystery, it exists as the major phase prior to and subsequent to protein crystal formation. Accordingly, adventitious materials, have the potential for destabilizing the host cubic phase. We have used low-angle x-ray diffraction to characterize the phases formed when hydrated monoolein in the cubic phase is combined with DM. Interestingly, the cubic phase tolerates high concentrations of the detergent but eventually destabilizes in favor of the lamellar phase. The transformation makes good sense given the complementary shapes of the detergent and monoolein molecules. The T-dependence of the DM-induced cubic-cubic and cubic-lamellar transitions determined under both equilibrium and metastable conditions shows that the cubic phase can be accessed and worked with down to 0° C with a DM concn. up to ca. 0.1M.