Abstract
Membrane-mediated interactions and aggregation of colloidal particles adsorbed to responsive elastic membranes are challenging problems relevant for understanding the microscopic organization and dynamics of biological membranes. We experimentally study the behavior of rodlike semiflexible fd virus particles electrostatically adsorbed to freestanding cationic lipid membranes and find that their behavior can be controlled by tuning the membrane charge and ionic strength of the surrounding medium. Three distinct interaction regimes of rodlike virus particles with responsive elastic membranes can be observed. (i) A weakly charged freestanding cationic lipid bilayer in a low ionic strength medium represents a gentle quasi-2D substrate preserving the integrity, structure, and mechanical properties of the membrane-bound semiflexible fd virus, which under these conditions is characterized by a monomer length of 884 ± 4 nm and a persistence length of 2.5 ± 0.2 μm, in perfect agreement with its properties in bulk media. (ii) An increase in the membrane charge leads to the membrane-driven collapse of fd virus particles on freestanding lipid bilayers and lipid nanotubes into compact globules. (iii) When the membrane charge is low, and the mutual electrostatic repulsion of membrane-bound virus particles is screened to a considerable degree, membrane-driven self-organization of membrane-bound fd virus particles into long linear tip-to-tip aggregates showing dynamic self-assembly/disassembly and quasi-semiflexible behavior takes place. These observations are in perfect agreement with the results of recent theoretical and simulation studies predicting that membrane-mediated interactions can control the behavior of colloidal particles adsorbed on responsive elastic membranes.
Highlights
As we have previously found in our experiments with DNA macromolecules adsorbed on freestanding cationic lipid bilayers,[29,30] semiflexible chains bound to a responsive elastic membrane undergo membrane-driven collapse
Scope and structure of the paper In the present paper, we experimentally study the interaction of monomer and polyphage fd virus particles with freestanding cationic lipid membranes mimicked by supergiant unilamellar vesicles[75] and cationic lipid nanotubes
(iii) When the electrostatic repulsion between fd virus particles bound to weakly charged freestanding cationic lipid membranes is screened by a surrounding medium with an ionic strength of B1 mM (Debye screening length B10 nm), membrane-mediated self-organization of virus particles takes place: membrane-bound rodlike particles form long tip-to-tip chain aggregates, which behave as semiflexible chains showing dynamic assembly– disassembly, conformational fluctuations, branching, and transient cyclization (Section 5)
Summary
Membrane-mediated interactions of macromolecules and colloids bound to elastic responsive lipid membranes have attracted a lot of attention because they represent a challenging problem of soft-matter physics,[1,2,3,4] and because of their biological significance.[5,6,7] Theoretical studies have demonstrated that local deformations of elastic membranes induced by the binding of colloids or macromolecules can result in attractive interactions capable of driving their clustering and self-organization.[8,9,10,11,12,13,14,15] These ideas have been beautifully. Local membrane deformations are expected to lead to a non-trivial behavior of a flexible polymer chain on an elastic lipid nanotube.[28] Further, semiflexible chains bound to deformable elastic membranes may undergo membrane-driven collapse into compact globules, which has been demonstrated experimentally[29,30] and explained theoretically.[13] On the other hand, rigid rodlike particles are predicted[31,32,33,34,35,36,37,38,39] to show membrane-driven self-organization controlled by the tension and curvature of the underlying membrane, which is believed to be relevant for understanding the biologically important issues of membrane budding and tubulation.[33,35,36] Interestingly, qualitatively similar modes of behavior and self-organization have recently been observed for colloids at liquid–liquid or liquid–air.
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