Structure and dynamics of crystalline protein layers bound to supported lipid bilayers.
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.
Horton
Margaret R
MR
Department für Physik, Ludwig-Maximilians-Universität, Geschwister-Scholl-Platz 1, 80539 München, Germany. mhorton@mit.edu
Reich
Christian
C
Gast
Alice P
AP
Rädler
Joachim O
JO
Nickel
Bert
B
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
D005456:Fluorescent Dyes; D008051:Lipid Bilayers; D046911:Macromolecular Substances; D011506:Proteins; D013113:Spin Labels; D014867:Water; D001360:Avidin; D019809:Streptavidin