Polymerization and Depolymerization of Actin Filaments

    Actin is one of the most abundant and highly conserved proteins in eukaryotic cells. The globular protein (G-actin) assembles into long filaments (F-actin), which form a variety of different networks within the cytoskeleton. Actin filaments grow and shrink by attachment and detachment of G-actin monomers at the two filament ends. These processes, which can be studied by Brownian Dynamics simulations [1], are coupled to nucleotide hydrolysis, a two-step process consisting of ATP cleavage and phosphate release. In principle, both processes could be cooperative, i.e., could depend on the local neighborhood of the subunit or protomer in the filament [2]. Such a doubly-cooperative process has been originally envisaged to explain the biphasic or intermittent behavior of filament depolymerization as observed experimentally.

    Recent single filament experiments provide strong evidence, however, that phosphate release represents a random, non-cooperative process. [3, 4]. In addition, a systematic theoretical analysis of the experimental data revealed that intermittent depolymerization of actin filaments is caused by photo-induced dimerization of actin protomers [5]. The stochastic dimerization process is triggered by random transitions of single, fluorescently labeled protomers. Each interruption of depolymerization represents the delayed dissociation of a single actin dimer, a single molecule event that can be directly observed in the optical microscope.


  • A. Jégou, T. Niedermayer, R. Lipowsky, M.-F. Carlier, and G. Romet-Lemonne
    On phosphate release in actin filaments.
     Biophys. J. 104, 2778-2779 (2013).

  • T, Niedermayer, A. Jégou, L. Chièze, B. Guichard, E. Helfer, G. Romet-Lemonne, M.-F. Carlier, and R. Lipowsky
    Intermittent depolymerization of actin filaments is caused by photo-induced dimerization of actin protomers.
     Intermittent depolymerization of actin ... - Supporting Information.
     PNAS 109, 10769-10774 (2012).

  • A. Jégou, T. Niedermayer, J. Orbán, D. Didry, R. Lipowsky, M.-F. Carlier, and G. Romet-Lemonne
    Individual actin filaments in a microfluidic flow reveal the mechanism of ATP hydrolysis and give Insight into the properties of profilin.
     Individual actin filaments ... - Supporting Information.
     PLoS Biology 9, e1001161 (2011).

  • Kunkun Guo, J. C. Shillcock, and R. Lipowsky
    Treadmilling of actin filaments via Brownian dynamics simulations.
     J. Chem. Phys. 133, 155105 (2010).

  • Xin Li, R. Lipowsky, and J. Kierfeld
    Coupling of actin hydrolysis and polymerization: Reduced description with two nucleotide states.
     EPL 89, 38010 (2010).

  • X. Li, J. Kierfeld, and R. Lipowsky
    Actin polymerization and depolymerization coupled to cooperative hydrolysis.
    Actin polymerization and depolymerization ... - EPAPS appendices.
     Phys. Rev. Lett. 103, 048102 (2009).

  • K. Guo, J. C. Shillcock, and R. Lipowsky
    Self-assembly of actin monomers into long filaments: Brownian dynamics simulations.
    J. Chem. Phys. 131, 015102 (2009).