Kinetics of Membrane Adhesion Mediated by Ligand–Receptor Interaction Studied with a Biomimetic System

Abstract

We report the first measurement of the kinetics of adhesion of a single giant vesicle controlled by the competition between membrane-substrate interaction mediated by ligand-receptor interaction, gravitation, and Helfrich repulsion. To model the cell-tissue interaction, we doped the vesicles with lipid-coupled polymers (mimicking the glycocalix) and the reconstituted ligands selectively recognized by alpha(IIb)beta(3) integrin-mediating specific attraction forces. The integrin was grafted on glass substrates to act as a target cell. The adhesion of the vesicle membrane to the integrin-covered surface starts with the spontaneous formation of a small (approximately 200 nm) domain of tight adhesion, which then gradually grows until the whole adhesion area is in the state of tight adhesion. The time of adhesion varies from few tens of seconds to about one hour depending on the ligand and lipopolymer concentration. At small ligand concentrations, we observed the displacement xi of the front of tight adhesion following the square root law xi approximately t(1/2), whereas, at high concentrations, we found a linear law xi approximately t. We show both experimentally and theoretically that the t(1/2)-regime is dominated by diffusion of ligands, and the xi approximately t-regime by the kinetics of ligands-receptors association.

Depletion versus Deflection: How Membrane Bending Can Influence Adhesion

“…Figure 3 If one fixes r n at a reasonable value for initial contact, then an estimate for the line tension follows from known depletion attractions. For the flexible membranes, Table I indicates 2:5 Â 10 À4 < E bend = r n 2 < 0:009 mN=m, so that for r n $ 1 m, 30 < b =r c < 1100 kT= m. These seemingly high line tensions are actually moderate (as they allow flexible membrane spreading), and agree with previous order 100 kT= m estimates [13]. With line tensions in the range 30-1000 kT= m, the measured value of b ¼ 9:6 kT suggests the radius of curvature at the contact line is on 10-300 nm.…”

“…In Table I, the resistance to adhesive spreading and the lag time seen for the stiff vesicles is similar to previous reports for bioadhesion between lightly functionalized vesicles [12,13]. The current lag time is eliminated by increasing membrane flexibility or depletion forces.…”

“…They predict arrested partial engulfment [9], prevention of spreading [10], instabilities [11], and snapping behavior [11]. Experimentally, a lag time for membrane deformation, followed by sudden spreading (suggestive of instability) has been reported in our [12] and another lab [13]. For instability-related lag times in avidin-biotindriven membrane adhesion, we formulated a competition between biomolecular adhesive energy and the bendingrelated line tension, b =r c , with r c equal to the radius of curvature of the bent region of the membrane [12].…”

“…Large line tensions are revealed, suggesting sharp membrane curvature at the contact line when an adhesive membrane engulfs a target. The study also provides examples of lag-time and snapping behaviors that differ from the phase separation-type instabilities reported for ligand-receptor binding at low membrane tensions [2,13].…”

Specific adhesion of membranes simultaneously supports dual heterogeneities in lipids and proteins

“…11,14 We have previously shown that non-specific membrane adhesion can promote the formation of an ordered lipid phase. 11 Traditionally, specific adhesion of membranes via protein-like binders [15][16][17][18][19] has been studied separately from lipid phase separation. Specific adhesion can produce heterogeneities in binding-protein distribution via equilibrium and kinetic mechanisms.…”