Authors: Y. Kaizuka and J.T. Groves
Affilation: University of California, Berkeley, United States
Pages: 428 - 430
Keywords: supported membrane, thermal fluctuation, interferometry, FRET
We have recently introduced a supported membrane junction system. The junction consists of a conventional supported bilayer membrane, on top of which a second bilayer membrane is deposited by rupture of a giant vesicle. This second (upper) membrane is stably associated with the lower supported membrane and the solid support. By incorporating fluorescently labeled lipid molecules in the membranes, two fluorescence imaging methods are enabled : intermembrane fluorescence resonance energy transfer (FRET) and optical standing wave interferometry. These reveal nanometer-scale topography of the membrane junction. We observed two distinct structures, a tight junction, in which two apposing membranes are closely associated(within 2nm), and a flexible junction, in which the two bilayers are rather loosely associated with each other (50nm separation). In the flexible junction the upper membrane exhibits thermal fluctuations with amplitudes of 5nm. We examine differences in the flexibility and fluidity of these structures by employing a phase separating mixture of phospholipids, cholesterol, and sphingolipids as a test system. The test composition was chosen because it resembles that of natural cell membranes. Results of there physical characterizations will be discussed.