title: Probing polymerization forces by using actin-propelled lipid vesicles.
abstract: Actin polymerization provides a powerful propulsion force for numerous types of cell motility. Although tremendous progress has been made in identifying the biochemical components necessary for actin-based motility, the precise biophysical mechanisms of force generation remain unclear. To probe the polymerization forces quantitatively, we introduce an experimental system in which lipid vesicles coated with the Listeria monocytogenes virulence factor ActA are propelled by actin polymerization. The polymerization forces cause significant deformations of the vesicle. We have used these deformations to obtain a spatially resolved measure of the forces exerted on the membrane using a model based on the competition between osmotic pressure and membrane stretching. Our results indicate that actin exerts retractile or propulsive forces depending on the local membrane curvature and that the membrane is strongly bound to the actin gel. These results are consistent with the observed dynamics. After a slow elongation of the vesicle from a spherical shape, the strong bonds between the actin gel and the membrane rupture if the retractile forces exceed a critical value, leading to a rapid release of the vesicle's trailing edge.
authors.affiliation: Department of Physics, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
authors.forename: Arpita
authors.initials: A
authors.lastname: Upadhyaya
authors.forename: Jeffrey R
authors.initials: JR
authors.lastname: Chabot
authors.forename: Albina
authors.initials: A
authors.lastname: Andreeva
authors.forename: Azadeh
authors.initials: A
authors.lastname: Samadani
authors.forename: Alexander
authors.initials: A
authors.lastname: van Oudenaarden
mesh_terms: D000199:Actins / Q000737:chemistry* / Q000502:physiology*; D000818:Animals; D001426:Bacterial Proteins / Q000502:physiology; D055592:Biophysical Phenomena; D001703:Biophysics; D001704:Biopolymers / Q000737:chemistry* / Q000502:physiology*; D002417:Cattle; D005782:Gels; D066298:In Vitro Techniques; D008081:Liposomes; D008089:Listeria monocytogenes / Q000502:physiology; D008565:Membrane Proteins / Q000502:physiology; D008954:Models, Biological; D020409:Molecular Motor Proteins / Q000502:physiology; D009068:Movement
chemical_list: D000199:Actins; D001426:Bacterial Proteins; D001704:Biopolymers; D005782:Gels; D008081:Liposomes; D008565:Membrane Proteins; D020409:Molecular Motor Proteins; C072980:actA protein, Listeria monocytogenes