Binding of actin filaments to charged lipid monolayers: Film balance experiments combined with neutron reflectivity

Abstract

The binding of polymerised actin-a prototype of semi-flexible macromolecule-to lipid monolayers is studied by neutron reflectivity to deduce the average thickness, the interfacial roughness and the polymer volume fraction of the adsorbed film. Electrostatic interaction between actin filaments (Factin) and the lipid monolayer is mediated through a cationic lipid (1,2-dimyristoyl-3-trimethylammoniumpropane, DMTAP). The adsorbed F-actin forms a monolayer with an average thickness of 69 to 84Å, depending on the ionic strength of the buffer and surface charge density of the monolayer. The volume fraction of F-actin in the adsorbed layer can be as high as 0.29. The thickness and high volume fraction of the actin layer suggest that actin filaments lie flat on the surface and form nematic ordering. The bindingunbinding equilibrium of F-actin is controlled by the ionic strength and exhibits a strong hysteresis. In contrast to the results obtained for filamentous actin, monomeric actin (G-actin) shows no detectable binding to the positively charged lipid layers.

Comparison of Actin- and Glass-Supported Phospholipid Bilayer Diffusion Coefficients

“…The diffusion coefficients for the glass-supported membranes (Fig. 3, triangles) also increased with temperature, but over a more narrow range (22)(23)(24)(25)(26)(27)(28)(29)(30) C). The main-phase transition temperature for each model membrane was determined via …”

“…As such, a planar membrane system with the inner leaflet supported by an actin cushion and the outer leaflet exposed to an aqueous environment would provide a highly physiologically relevant system for investigating membrane biophysics. Previous work (reviewed by Vogel and Schwille (25)) has investigated actin interactions with lipid monolayers (26), biofunctionalized monolayers (27), and bilayers (28). Actin has been encapsulated inside giant unilamellar vesicles for the study of membrane organization (29) and the mechanical influence on the hybrid membrane system (30).…”

“…Actin has been encapsulated inside giant unilamellar vesicles for the study of membrane organization (29) and the mechanical influence on the hybrid membrane system (30). Additionally, F-actin has been investigated as an inducer of single ionic channels (31) and separately, the binding affinity of actin to phospholipid monolayers has been studied (26,27).…”

Design of Biofunctional Assemblies on Solids through Recombinant Spherical Bacterial Protein Lumazine Synthase

“…In contrast, the binding/unbinding transition by electrostatic forces is associated with a very large hysteresis. [25] Surface-grafted actin filaments (which are separated from the protein-damaging glass surfaces) could serve as trails for the local transport of cargo-loaded vesicles on biofunctional surfaces through actin ± myosin motors.…”

Biomimetic Liposome Model Systems to Study Cell Shape Control by the Cytoskeleton

“…The high surface charges of the lipid head groups probably shield the charge on the actin monomers and thus facilitate monomer-monomer contact [183]. The electrostatic interaction of actin filaments and positively charged (DMTAP) or zwitterionic (PC) lipids is reversible through addition of a high ionic strength buffer (>65 mM KCl) [88,184,185]. Surprisingly, actin filaments can also adsorb to negatively charged lipids, such as phosphatidylserine (PS), provided that the divalent cation concentration is raised to 6-12 mM Mg 2+ [186].…”