title: Ripples and the formation of anisotropic lipid domains: imaging two-component supported double bilayers by atomic force microscopy.
abstract: Direct visualization of the fluid-phase/ordered-phase domain structure in mica-supported bilayers composed of 1,2-dimyristoyl-sn-glycero-3-phosphocholine/1,2-distearoyl-sn-glycero-3-phosphocholine mixtures is performed with atomic force microscopy. The system studied is a double bilayer supported on a mica surface in which the top bilayer (which is not in direct contact with the mica) is visualized as a function of temperature. Because the top bilayer is not as restricted by the interactions with the surface as single supported bilayers, its behavior is more similar to a free-standing bilayer. Intriguing straight-edged anisotropic fluid-phase domains were observed in the fluid-phase/ordered-phase coexistence temperature range, which resemble the fluid-phase/ordered-phase domain patterns observed in giant unilamellar vesicles composed of such phospholipid mixtures. With the high resolution provided by atomic force microscopy, we investigated the origin of these anisotropic lipid domain patterns, and found that ripple phase formation is directly responsible for the anisotropic nature of these domains. The nucleation and growth of fluid-phase domains are found to be directed by the presence of ripples. In particular, the fluid-phase domains elongate parallel to the ripples. The results show that ripple phase formation may have implications for domain formation in biological systems.
authors.affiliation: Section of Molecular and Cellular Biology, University of California-Davis, One Shields Avenue, Davis, CA 95616, USA. ckidy@kemi.dtu.dk
authors.forename: Chad
authors.initials: C
authors.lastname: Leidy
authors.forename: Thomas
authors.initials: T
authors.lastname: Kaasgaard
authors.forename: John H
authors.initials: JH
authors.lastname: Crowe
authors.forename: Ole G
authors.initials: OG
authors.lastname: Mouritsen
authors.forename: Kent
authors.initials: K
authors.lastname: Jørgensen
mesh_terms: D016880:Anisotropy; D055592:Biophysical Phenomena; D001703:Biophysics; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry*; D008051:Lipid Bilayers / Q000737:chemistry*; D008055:Lipids / Q000737:chemistry*; D008567:Membranes, Artificial; D018625:Microscopy, Atomic Force; D010713:Phosphatidylcholines / Q000737:chemistry*; D013696:Temperature
chemical_list: D008051:Lipid Bilayers; D008055:Lipids; D008567:Membranes, Artificial; D010713:Phosphatidylcholines; D004134:Dimyristoylphosphatidylcholine