title: The effect of diffusion, depolymerization and nucleation promoting factors on actin gel growth.
abstract: In eukaryotic cells, localized actin polymerization is able to deform the plasma membrane and push the cell forward. Depolymerization of actin filaments and diffusion of actin monomers ensure the availability of monomers at sites of polymerization, and therefore these processes must play an active role in cellular actin dynamics. Here we reveal experimental evidence that actin gel growth can be limited by monomer diffusion, consistent with theoretical predictions. We study actin gels formed on beads coated with ActA (and ActA fragments), the bacterial factor responsible for actin-based movement of Listeria monocytogenes. We observe a saturation of gel thickness with increasing bead radius, the signature of diffusion control. Data analysis using an elastic model of actin gel growth gives an estimate of 2x10(-8) cm(-2) s(-1) for the diffusion coefficient of actin monomers through the gel, ten times less than in buffer, and in agreement with literature values in bulk cytoskeleton, providing corroboration of our model. The depolymerization rate of actin filaments and the elastic modulus of the gel are also evaluated. Furthermore, we qualitatively examine the different actin gels produced when ActA fragments interact with either VASP or the Arp2/3 complex.
authors.affiliation: Laboratoire Physicochimie Curie, UMR168 Institut Curie/CNRS, Paris, France.
authors.forename: Julie
authors.initials: J
authors.lastname: Plastino
authors.forename: Ioannis
authors.initials: I
authors.lastname: Lelidis
authors.forename: Jacques
authors.initials: J
authors.lastname: Prost
authors.forename: Cécile
authors.initials: C
authors.lastname: Sykes
mesh_terms: D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins / Q000737:chemistry* / Q000648:ultrastructure*; D001426:Bacterial Proteins / Q000737:chemistry*; D015815:Cell Adhesion Molecules / Q000737:chemistry*; D002457:Cell Extracts / Q000737:chemistry; D020099:Coated Materials, Biocompatible / Q000737:chemistry; D003198:Computer Simulation; D003460:Crystallization / Q000379:methods*; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000648:ultrastructure; D004058:Diffusion; D019281:Dimerization; D004548:Elasticity; D005782:Gels / Q000737:chemistry; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000737:chemistry*; D008840:Microfilament Proteins; D008956:Models, Chemical; D008958:Models, Molecular; D046912:Multiprotein Complexes / Q000737:chemistry / Q000648:ultrastructure; D010750:Phosphoproteins / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry; D011485:Protein Binding; D011487:Protein Conformation; D000098662:Vasodilator-Stimulated Phosphoprotein
chemical_list: C495926:ACTR2 protein, human; C495928:ACTR3 protein, human; D051377:Actin-Related Protein 2; D051378:Actin-Related Protein 3; D000199:Actins; D001426:Bacterial Proteins; D015815:Cell Adhesion Molecules; D002457:Cell Extracts; D020099:Coated Materials, Biocompatible; D003598:Cytoskeletal Proteins; D005782:Gels; D008565:Membrane Proteins; D008840:Microfilament Proteins; D046912:Multiprotein Complexes; D010750:Phosphoproteins; D011108:Polymers; D000098662:Vasodilator-Stimulated Phosphoprotein; C072980:actA protein, Listeria monocytogenes