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Soft Matter and Biological Physics

Eur. Phys. J. E 2, 125-136

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

B. Demé1 - D. Hess1 - M. Tristl1 - Lay-Theng Lee2 - E. Sackmann1

1 Technische Universität München, Physik Department, Lehrstuhl für Biophysik E22, James-Franck-Str., D-85747 Garching, Germany
2 Laboratoire Léon Brillouin, CEA-CNRS, Centre d'Études de Saclay, F-91191 Gif sur Yvette, France
deme@ill.fr

Received 11 August 1999

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 (F-actin) and the lipid monolayer is mediated through a cationic lipid (1,2-dimyristoyl-3-trimethylammonium-propane, DMTAP). The adsorbed F-actin forms a monolayer with an average thickness of 69 to 84 Å, 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 binding-unbinding 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.

PACS
61.12.Ha Neutron reflectometry - 68.55.Jk Structure and morphology; thickness

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