BIOMIMETIC MEMBRANES SOLUBILIZATION BY DETERGENTS WITH DIFFERENT PHYSICOCHEMICAL CHARACTERISTICS

Detergents are amphiphilic molecules used in biological membranes solubilization, allowing the extraction of membrane components. There is a wide range of detergents available, which have different physicochemical characteristics and act in different ways in the solubilization of biomembranes. Cell membranes are also diverse, as they are made up of different types of lipids and may have different properties, such as more fluid characteristic, as in the liquid-disordered (Ld) phase, or a more ordered character, similar to the liquid-ordered (Lo) phase, which can occur in transient microdomains called lipid rafts. The present work investigates the detergents TX-100, Triton X-165, C10E5, Dodecyl Maltoside (DDM), Octyl Glycoside (OG) (non-ionic), SDS (anionic), CHAPS (zwitterionic) and CTAB (cationic). The membranes compositions subjected to solubilization were pure POPC (Ld phase), SM:Col, 7:3 (Lo phase) and the biomimetic ternary mixture (POPC:SM:Col, 2:1:2). Turbidity measurements of were used to follow the solubilization profile of large unilamellar vesicles (LUVs) along the titration with detergents and optical microscopy of giant unilamellar vesicles (GUVs) allowed direct visualization of the impact of the detergents on the different membrane compositions. The results show that only pure POPC is completely solubilized by most of the detergents and that the presence of cholesterol leads to partially or fully insoluble membranes. The non-ionic detergents TX-100, TX-165 and C10E5 could clearly flip-flop across POPC membranes, causing an increase in vesicle size, whereas the detergents with bulky or charged headgroups could insert only into the outer leaflet and caused vesicle burst. All detergents, except DDM and SDS, were able to rearrange the ternary mixture and promote macroscopic Ld/Lo phase separation with preferential solubilization of the Ld phase. We conclude that the character and size of the polar head modulate the ability of the detergent to perform flip-flop during the incorporation stage and are important to an efficient solubilization of POPC. The presence of cholesterol decreases considerably the membrane solubility for all detergents but most detergents are able to insert in the biomimetic composition and cause lateral phase separation.