Regensburg 2007 – scientific programme

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BP: Fachverband Biologische Physik

BP 3: Membranes and Interfaces

BP 3.7: Talk

Monday, March 26, 2007, 15:45–16:00, H43

Structure and dynamics of crystalline protein layers peripherally bound to supported lipid bilayers — •Christian Reich, Margaret Horton, Joachim Rädler, and Bert Nickel — Department für Physik, Ludwig-Maximilians-Universität, D-80539 München

We model peripheral membrane proteins at the surface of cell 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 a protein layer containing two-dimensional streptavidin crystals bound to a SLB. A single lipid bilayer provides a biologically-relevant environment for in-situ investigation of membrane-associated proteins interacting with lipids. Using continuous bleaching, we measure a 10-15% decrease in the fluidity of the SLB after protein layer formation. We propose that this reduction in lipid mobility is due to a small fraction ca. 0.04 of immobilized lipids bound to the protein layer that create obstacles to membrane diffusion. Fits to our X-ray reflectivity data show a ca. 40 Å thick layer of protein and we resolve the ca. 8 Å 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. Finally, we show how complementary information can be obtained in neutron experiments at REFSANS (FRM2).