Surface-Induced Polymerization of Actin

Abstract

Living cells contain a very large amount of membrane surface area, which potentially influences the direction, the kinetics, and the localization of biochemical reactions. This paper quantitatively evaluates the possibility that a lipid monolayer can adsorb actin from a nonpolymerizing solution, induce its polymerization, and form a 2D network of individual actin filaments, in conditions that forbid bulk polymerization. G- and F-actin solutions were studied beneath saturated Langmuir monolayers containing phosphatidylcholine (PC, neutral) and stearylamine (SA, a positively charged surfactant) at PC:SA = 3:1 molar ratio. Ellipsometry, tensiometry, shear elastic measurements, electron microscopy, and dark-field light microscopy were used to characterize the adsorption kinetics and the interfacial polymerization of actin. In all cases studied, actin follows a monoexponential reaction-limited adsorption with similar time constants (approximately 10(3) s). At a longer time scale the shear elasticity of the monomeric actin adsorbate increases only in the presence of lipids, to a 2D shear elastic modulus of mu approximately 30 mN/m, indicating the formation of a structure coupled to the monolayer. Electron microscopy shows the formation of a 2D network of actin filaments at the PC:SA surface, and several arguments strongly suggest that this network is indeed causing the observed elasticity. Adsorption of F-actin to PC:SA leads more quickly to a slightly more rigid interface with a modulus of mu approximately 50 mN/m.

Spectroscopic studies of self-assembled TPPS4nanostructures in aqueous solutions: The role of serum albumin and pH

“…We suggest that during the interaction proteins act as centres of condensation for monomeric (H + ) 2 TPPS 4 species, thus facilitating the formation of J-aggregates on the surface of protein moiety. Similar surface-induced polymerization processes were reported for monomeric actin on a positively charged lipid monolayer [18]. High concentration of BSA disrupts these aggregates forming the protein-porphyrin complex absorbing at 421 nm.…”

The role of lipid–protein interactions in amyloid-type protein fibril formation

“…This was demonstrated for the lipid-induced polymerization of actin (Renault et al, 1999). More specifically, it was found that chemically identical lipid surfaces behave differently when present as monolayers or liposomal bilayers.…”

“…The mechanisms of surface-induced fibrillization may be fundamentally different from that occuring in bulk solution because of the restrictions imposed by the dimensionality of the system and the physicochemical and dynamic properties of the surface (Zhu et al, 2002(Zhu et al, , 2004Renault et al, 1999). This was demonstrated for the lipid-induced polymerization of actin (Renault et al, 1999).…”

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

“…Actin is an anionic protein that has been shown to interact with charged lipids, in both the monomeric (G-actin) and polymeric (F-actin) forms (53). Additionally, liposomes have been shown to induce G-actin to form F-actin, a process that is charge-dependent (54).…”