Solubilization of supported lipid membranes by octyl glucoside observed by time-lapse atomic force microscopy

Detergents are very useful for the purification of membrane proteins. A good detergent for protein extraction has to prevent denaturation by unfolding, and to avoid aggregation. Therefore, gaining access to the mechanism of biomembranes' solubilization by detergents is crucial in biochemical research. Among the wide range of detergents used to purify membrane proteins, n-octyl beta-D-glucopyranoside (OG) is one of the most important as it can be easily removed from final protein extracts. Here, we used real-time atomic force microscopy (AFM) imaging to visualize the behavior of a model supported lipid bilayer in the presence of OG. Two kinds of supported model membranes were prepared by fusion of unilamellar vesicles: with an equimolar mixing of dioleoylphosphatidylcholine/dipalmitoylphosphatidylcholine (DOPC/DPPC) or with DPPC alone. Time-lapse AFM experiments evidenced that below its critical micelle concentration (CMC), OG was not able to solubilize the bilayer but the gel DPPC domains were instantly dissolved into the DOPC matrix. This result was interpreted as a disorganization of the DPPC molecular packing induced by OG. When membranes were incubated with OG at concentrations higher than CMC, the detergent immediately provoked the complete and immediate desorption of the whole bilayer for both compositions: DPPC and DOPC/DPPC. After a while, some patches appeared onto the bare mica surface. This redeposition activity, together with fusion events, progressively led to the recovery of a continuous bilayer. These results provide a new insight on the unique properties of OG employed in membrane reconstitution protocols.