Structure and Dynamics of Supported Intermembrane Junctions

Abstract

Supported intermembrane junctions, formed by rupture of giant unilamellar vesicles onto conventional supported lipid membranes, have recently emerged as model systems for the study of biochemical processes at membrane interfaces. Using intermembrane fluorescence resonance energy transfer and optical standing wave fluorescence interferometry, we characterize the nanometer-scale topography of supported intermembrane junctions and find two distinct association states. In one state, the two membranes adhere in close apposition, with intermembrane separations of a few nanometers. In the second state, large intermembrane spacings of approximately 50 nm are maintained by a balance between Helfrich (entropic) repulsion and occasional sites of tight adhesion that pin the two membranes together. Reversible transitions between these two states can be triggered with temperature changes. We further examine the physical properties of membranes in each state using a membrane mixture near its miscibility phase transition temperature. Thermodynamic characteristics of the phase transition and diffusive mobility of individual lipids are comparable. However, collective Brownian motion of phase-separated domains and compositional fluctuations are substantially modulated by intermembrane spacing. The scaling properties of diffusion coefficient with particle size are determined from detailed analysis of domain motion in the different junction types. The results provide experimental verification of a theoretical model for two-dimensional mobility in membranes, which includes frictional coupling across an interstitial water layer.

Efficient elusion of viable adhesive cells from a microfluidic system by air foam

“…Supported lipid bilayer (SLB), an artificial mimic of the natural cell membrane, which is compatible with protein incorporation and possesses sustained lateral mobility, [20][21][22][23][24][25][26] has been studied extensively as model system of biological membranes over past decades. Previously, many studies have demonstrated that this biomimetic multifunctional material has great bioinert property and lateral mobility, thus leading to effective resistance of non-specific proteins adsorption and cells adhesion.…”

Protein patterns at lipid bilayer junctions

“…Lipid bilayers can be readily interfaced with solid substrates while retaining their natural 2D fluidity (11)(12)(13); half of our junction consists of such a supported bilayer, assembled on SiO 2 . A single species of protein (an IgG antibody) is bound to the supported bilayer, and a ruptured giant lipid vesicle (14,15) provides the second lipid bilayer half of the intermembrane junction. The quasi-planar geometry allows us to image the intermembrane topography via several concurrent, complementary techniques: direct fluorescence microscopy, intermembrane fluorescence resonance energy transfer (FRET) microscopy (16)(17)(18)(19), and fluorescence interference contrast (FLIC) microscopy (14-18, 20, 21).…”

Nanorheology of viscoelastic shells: Applications to viral capsids

“…To allow any radial deformations of the impermeable bilayer, there must be some area change of the surface. One may imagine that the surface of a tensed GUV is essentially inextensible, however, even such tensed structures contain a reservoir of extra area hidden in the (small-scale) thermal undulations of the surface [13,40]. Thus the two-dimensional bulk modulus of the viscous shell is dominated by a large, but finite elastic component.…”