title: Kinetic overshoot in actin network assembly induced jointly by branching and capping proteins.
abstract: We report an experimental study of the kinetics of actin assembly mediated by branching and capping proteins. Our findings confirm the recent prediction of a "branching explosion" occurring during polymerization. Fluorescence imaging shows a number of actin filaments with branches within a few minutes of polymerization, induced by the activated branching protein complex Arp2/3, but the number of visible branches decreases over time. The light-scattering intensity displays an overshoot as a function of time, which we attribute to the formation of highly branched clusters early in polymerization. Furthermore, the overshoot occurs over a limited range of the ratio of concentrations of branching and capping proteins, also consistent with the theoretical model. These results establish a natural link between the kinetic theory of actin assembly in vitro and the cytoskeletal structure and actin dynamics in motile cells.
authors.affiliation: Physics Department, Brown University, Providence, Rhode Island 02912, USA.
authors.forename: Hyeran
authors.initials: H
authors.lastname: Kang
authors.forename: Anders E
authors.initials: AE
authors.lastname: Carlsson
authors.forename: Jay X
authors.initials: JX
authors.lastname: Tang
mesh_terms: D051376:Actin-Related Protein 2-3 Complex / Q000494:pharmacology*; D000199:Actins / Q000737:chemistry* / Q000378:metabolism*; D000818:Animals; D018260:Gelsolin / Q000494:pharmacology*; D006801:Humans; D007700:Kinetics; D008027:Light; D008856:Microscopy, Fluorescence; D055503:Protein Multimerization / Q000187:drug effects*; D020836:Protein Structure, Quaternary; D011817:Rabbits; D012542:Scattering, Radiation
chemical_list: D051376:Actin-Related Protein 2-3 Complex; D000199:Actins; D018260:Gelsolin