The membrane proteins (MPs) alpha-synuclein (ASYN) and bacteriorhodopsin (BR) were readily incorporated into bicontinuous microemulsions (BMEs) formed by two microemulsion systems: water/heptane/Aerosol-OT (AOT)/CK-2,13 and water/dodecane/sodium dodecyl sulfate (SDS)/1-pentanol. (CK-2,13 is an alkyl ethoxylate possessing two alkyl tail groups of carbon chain length 2 and 13 and an average degree of ethoxylation of 5.6.) MPs were encapsulated in BMEs through preparation of Winsor-III systems at optimal salinity, with the anionic surfactants AOT and SDS providing the driving force for extraction. Dissolution of ASYN in BMEs greatly increased the former’s alpha-helicity, similar to ASYN’s behavior in the presence of biomembranes, while BME- and vesicle-encapsulated BR possessed similar secondary structure. Small-angle neutron scattering (SANS) results clearly demonstrated the direct interaction of MPs with the surfactants, resulting in a decrease of surface area per volume for surfactant monolayers due to decreased surfactant efficiency. The SANS signal for ASYN was isolated through the use of neutron contrast matching for the surfactants through partial deuteration of water and oil, one of the first reports of contrast matching for BMEs in the literature. The SANS results of the contrast matched sample reflected similar aggregation for ASYN in BMEs as was reported previously for vesicles and SDS solution. This study demonstrates the potential use of BMEs as MP host systems for conducting biochemical reactions such as the conversion of sunlight into adenosine triphosphate (ATP) by BR and studying fundamental behavior of MPs, such as the role of ASYN dysfunction in Parkinson’s disease, as well as for isolation and purification of MPs via Winsor-III -based extraction.

Circular dichroism spectroscopic data reported herein was obtained directly from the instrument. The CONTIN program was used to fit the spectroscopic data, to obtain an estimate of the distribution of secondary structure for the proteins. Small-angle neutron scattering (SANS) data provided herein was obtained from the Bio-SANS instrument at Oak Ridge National Laboratory (Oak Ridge, TN, USA), and reduced and processed in a standard fashion. Microsoft Excel was employed to obtain linear fits to SANS data, as described in the spreadsheets and readme file.