title: Cholesterol modulation of membrane resistance to Triton X-100 explored by atomic force microscopy.
abstract: Biomembranes are not homogeneous, they present a lateral segregation of lipids and proteins which leads to the formation of detergent-resistant domains, also called "rafts". These rafts are particularly enriched in sphingolipids and cholesterol. Despite the huge body of literature on raft insolubility in non-ionic detergents, the mechanisms governing their resistance at the nanometer scale still remain poorly documented. Herein, we report a real-time atomic force microscopy (AFM) study of model lipid bilayers exposed to Triton X-100 (TX-100) at different concentrations. Different kinds of supported bilayers were prepared with dioleoylphosphatidylcholine (DOPC), sphingomyelin (SM) and cholesterol (Chol). The DOPC/SM 1:1 (mol/mol) membrane served as the non-resistant control, and DOPC/SM/Chol 2:1:1 (mol/mol/mol) corresponded to the raft-mimicking composition. For all the lipid compositions tested, AFM imaging revealed that TX-100 immediately solubilized the DOPC fluid phase leaving resistant patches of membrane. For the DOPC/SM bilayers, the remaining SM-enriched patches were slowly perforated leaving crumbled features reminiscent of the initial domains. For the raft model mixture, no holes appeared in the remaining SM/Chol patches and some erosion occurred. This work provides new, nanoscale information on the biomembranes' resistance to the TX-100-mediated solubilization, and especially about the influence of Chol.
authors.affiliation: Laboratoire de Biomécanique et Génie Biomédical, UMR-CNRS 6600, Université de Technologie de Compiègne, BP 20529, 60205 Compiègne Cedex, France.
authors.forename: Karim
authors.initials: K
authors.lastname: El Kirat
authors.forename: Sandrine
authors.initials: S
authors.lastname: Morandat
mesh_terms: D002784:Cholesterol / Q000737:chemistry*; D004351:Drug Resistance; D008051:Lipid Bilayers / Q000737:chemistry*; D008560:Membrane Fluidity; D021962:Membrane Microdomains / Q000737:chemistry* / Q000648:ultrastructure*; D018625:Microscopy, Atomic Force; D017830:Octoxynol / Q000737:chemistry*
chemical_list: D008051:Lipid Bilayers; D017830:Octoxynol; D002784:Cholesterol