Surface-induced polymerization of actin.
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.
Laboratoire de Spectrométrie Physique, Centre National de la Recherche Scientifique, UMR-5588, BP87, 38402 St Martin d'Heres, France.
A
A
Renault
P F
PF
Lenne
C
C
Zakri
A
A
Aradian
C
C
Vénien-Bryan
F
F
Amblard
D000199:Actins / Q000737:chemistry* / Q000378:metabolism / Q000648:ultrastructure; D000327:Adsorption; D000818:Animals; D055592:Biophysical Phenomena; D001703:Biophysics; D001704:Biopolymers / Q000737:chemistry / Q000378:metabolism; D002645:Chickens; D004548:Elasticity; D066298:In Vitro Techniques; D007700:Kinetics; D008563:Membrane Lipids / Q000737:chemistry / Q000378:metabolism; D008854:Microscopy, Electron; D013499:Surface Properties; D013500:Surface Tension
D000199:Actins; D001704:Biopolymers; D008563:Membrane Lipids