title: Imaging of reconstituted purple membranes by atomic force microscopy.
abstract: The organization of bacteriorhodopsin (bR) within reconstituted purple membranes (RPM) was examined using atomic force microscopy (AFM). Five reconstituted species were examined: RPM 3 (bR/native polar lipids/dimyristoylphosphatidylcholine (DMPC) in a 1:9:14 molar ratio), RPM 4 (bR/native polar lipids in a 1:7 molar ratio), RPM 5 (bR/native polar lipids/1,2-di-O-phytanyl-sn-glycerol in a 1:3.5:6.1 molar ratio), RPM 6 (bR/native polar lipids/1,2-di-O-phytanyl-sn-glycero-3-phosphocholine in a 1:3.5:4.9 molar ratio), and RPM 7 (bR/native polar lipids/1,2-diphytanoyl-sn-glycero-3-[phospho-L-serine] in a 1:3.5:4.6 molar ratio). RPM 3 patches adsorbed onto mica exhibit domains of crystallized bR trimers arranged in a hexagonal packing structure, similar to those found in native purple membrane (NPM). These domains are enclosed by DMPC-rich regions. RPM 4 patches were observed to have larger domains of crystallized bR, with trimer orientation 30 degrees different from that found in NPM. The bR-rich domains are enclosed by a large, protein-free, lipid-rich region. The topography of RPM 5 was difficult to resolve as the surface had no discernable patterns or structure. The topographies of RPM 6 and 7 were similar to that found in RPM 3 in that higher domains were formed within the patch adsorbed onto mica. They may contain protein-rich regions, but clear images of protein arrangement could not be obtained using AFM. This may be a result of imaging limitations or of the lack of organization of bR within these domains.
authors.affiliation: Department of Chemical Engineering, University of California, 201 Gilman Hall, Berkeley, CA 94720-1462, USA.
authors.forename: David T
authors.initials: DT
authors.lastname: Kim
authors.forename: Harvey W
authors.initials: HW
authors.lastname: Blanch
authors.forename: Clayton J
authors.initials: CJ
authors.lastname: Radke
mesh_terms: D000327:Adsorption; D001436:Bacteriorhodopsins / Q000737:chemistry* / Q000648:ultrastructure; D004134:Dimyristoylphosphatidylcholine / Q000737:chemistry; D008055:Lipids / Q000737:chemistry; D008081:Liposomes / Q000737:chemistry*; D018625:Microscopy, Atomic Force / Q000379:methods; D010715:Phosphatidylglycerols / Q000737:chemistry; D011506:Proteins / Q000737:chemistry; D018717:Purple Membrane / Q000737:chemistry* / Q000145:classification / Q000648:ultrastructure
chemical_list: D008055:Lipids; D008081:Liposomes; D010715:Phosphatidylglycerols; D011506:Proteins; D001436:Bacteriorhodopsins; D004134:Dimyristoylphosphatidylcholine