Circular dichroism spectroscopic and small-angle neutron scattering analysis of alpha-synuclein and bacteriorhodopsin in bicontinuous microemulsions

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 m...