title: Structure and dynamics of crystalline protein layers bound to supported lipid bilayers.
abstract: We study proteins at the surface of bilayer membranes using streptavidin and avidin bound to biotinylated lipids in a supported lipid bilayer (SLB) at the solid-liquid interface. Using X-ray reflectivity and simultaneous fluorescence microscopy, we characterize the structure and fluidity of protein layers with varied relative surface coverages of crystalline and noncrystalline protein. With continuous bleaching, we measure a 10-15% decrease in the fluidity of the SLB after the full protein layer is formed. We propose that this reduction in lipid mobility is due to a small fraction (0.04) of immobilized lipids bound to the protein layer that create obstacles to membrane diffusion. Our X-ray reflectivity data show a 40 A thick layer of protein, and we resolve an 8 A layer separating the protein layer from the bilayer. We suggest that the separation provided by this water layer allows the underlying lipid bilayer to retain its fluidity and stability.
authors.affiliation: Department für Physik, Ludwig-Maximilians-Universität, Geschwister-Scholl-Platz 1, 80539 München, Germany. mhorton@mit.edu
authors.forename: Margaret R
authors.initials: MR
authors.lastname: Horton
authors.forename: Christian
authors.initials: C
authors.lastname: Reich
authors.forename: Alice P
authors.initials: AP
authors.lastname: Gast
authors.forename: Joachim O
authors.initials: JO
authors.lastname: Rädler
authors.forename: Bert
authors.initials: B
authors.lastname: Nickel
mesh_terms: D000818:Animals; D001360:Avidin / Q000737:chemistry; D003460:Crystallization; D004058:Diffusion; D005456:Fluorescent Dyes; D066298:In Vitro Techniques; D008051:Lipid Bilayers / Q000737:chemistry*; D046911:Macromolecular Substances / Q000737:chemistry; D008560:Membrane Fluidity; D008856:Microscopy, Fluorescence; D008958:Models, Molecular; D011506:Proteins / Q000737:chemistry*; D013113:Spin Labels; D055672:Static Electricity; D019809:Streptavidin / Q000737:chemistry; D014867:Water / Q000737:chemistry
chemical_list: D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D011506:Proteins; D013113:Spin Labels; D014867:Water; D001360:Avidin; D019809:Streptavidin