title: Supported planar bilayers from hexagonal phases.
abstract: In this work the presence of inverted hexagonal phases H(II) of 1-palmitoy-2-oleoyl-sn-glycero-3-phosphoethanolamine (POPE) and cardiolipin (CL) (0.8:0.2, mol/mol) in the presence of Ca(2+) were observed via (31)P-NMR spectroscopy. When suspensions of the same composition were extended onto mica, H(II) phases transformed into structures which features are those of supported planar bilayers (SPBs). When characterized by atomic force microscopy (AFM), the SPBs revealed the existence of two laterally segregated domains (the interdomain height being approximately 1 nm). Cytochrome c (cyt c), which binds preferentially to acidic phospholipids like CL, was used to demonstrate the nature of the domains. We used 1-anilinonaphtalen-8-sulfonate (ANS) to demonstrate that in the presence of cyt c, the fluorescence of ANS decreased significantly in lamellar phases. Conversely, the ANS binding to H(II) phases was negligible. When cyt c was injected into AFM fluid imaging cells, where SPBs of POPE:CL had previously formed poorly defined structures, protein aggregates ( approximately 100 nm diameter) were ostensibly observed only on the upper domains, which suggests not only that they are mainly formed by CL, but also provides evidence of bilayer formation from H(II) phases. Furthermore, a model for the nanostructure of the SPBs is herein proposed.
authors.affiliation: Departament de Química-Física, Facultat de Química, Spain.
authors.forename: Oscar
authors.initials: O
authors.lastname: Domènech
authors.forename: Antoni
authors.initials: A
authors.lastname: Morros
authors.forename: Miquel E
authors.initials: ME
authors.lastname: Cabañas
authors.forename: M
authors.initials: M
authors.lastname: Teresa Montero
authors.forename: Jordi
authors.initials: J
authors.lastname: Hernández-Borrell
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry; D000817:Anilino Naphthalenesulfonates; D002118:Calcium / Q000737:chemistry; D002308:Cardiolipins / Q000737:chemistry* / Q000378:metabolism; D045304:Cytochromes c / Q000737:chemistry* / Q000378:metabolism; D005456:Fluorescent Dyes; D008051:Lipid Bilayers / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D018625:Microscopy, Atomic Force; D008958:Models, Molecular; D008968:Molecular Conformation; D049329:Nanostructures; D010714:Phosphatidylethanolamines / Q000737:chemistry* / Q000378:metabolism; D011485:Protein Binding
chemical_list: D000538:Aluminum Silicates; D000817:Anilino Naphthalenesulfonates; D002308:Cardiolipins; D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D010714:Phosphatidylethanolamines; C057561:1-palmitoyl-2-oleoylphosphatidylethanolamine; C027132:1-anilino-8-naphthalenesulfonate; D045304:Cytochromes c; D002118:Calcium; C011934:mica