Analysis of shape, fluctuations, and dynamics in intermembrane junctions

Abstract

A dynamic-elastic model for weakly adhered intermembrane junctions is presented. Helfrich membrane energetics coupled to hydrodynamic modes of the surrounding solvent reproduce the average shape, fluctuations, and dynamics of these junctions as measured experimentally. Comparison between numerical results and experimental data provides the first direct measure of surface tension in these systems (0.01-0.06 dyn/cm). The measurements suggest bilayer-bilayer adhesion energetics as the dominant source of surface tension in the experimental systems.

FIGURE 1

(Top row) Average bilayer shape for a representative configuration of pinning sites in a Type-2 intermembrane junction. The left panel displays the predicted average membrane shape 〈h(r)〉 assuming physical constants detailed in Table 1. The middle panel displays the predicted average FLIC image 〈h_m(r)〉 corresponding to the same simulation. The right panel contains the experimental FLIC data (8). The triangle in the left image marks the location considered for dynamics as displayed in Fig. 2. (Bottom row) Analogous cases to the top row, but displaying fluctuations around the average and . In all panels, the z-axis is expanded relative to x, y to emphasize detail. In this and subsequent figures, the value κ = 7 × 10⁻¹² ergs is assumed.

FIGURE 2

Plot of a typical time-correlation functions , where , without the convolution over G(r) (dashed line) or , with the convolution over G(r) (solid line). This particular decay reflects measurement at the point indicated by the triangle in the upper-left plot in Fig. 1.

FIGURE 3

Plot of the average correlation function and variance in this average, assuming results are extracted from a finite data set of duration τ ∼ 17s, τ ∼ 88 s, and τ ∼ 176 s for the left, middle, and right panels, respectively. The results here reflect the time correlations at the point indicated in the upper-left plot in Fig. 1.