Capping Protein Increases the Rate of Actin-Based Motility by Promoting Filament Nucleation by the Arp2/3 Complex

Department of Cellular and Molecular Pharmacology, School of Medicine, University of California, San Francisco, San Francisco, CA 94143, USA.
Cell (Impact Factor: 32.24). 06/2008; 133(5):841-51. DOI: 10.1016/j.cell.2008.04.011
Source: PubMed


Capping protein (CP) is an integral component of Arp2/3-nucleated actin networks that drive amoeboid motility. Increasing the concentration of capping protein, which caps barbed ends of actin filaments and prevents elongation, increases the rate of actin-based motility in vivo and in vitro. We studied the synergy between CP and Arp2/3 using an in vitro actin-based motility system reconstituted from purified proteins. We find that capping protein increases the rate of motility by promoting more frequent filament nucleation by the Arp2/3 complex and not by increasing the rate of filament elongation as previously suggested. One consequence of this coupling between capping and nucleation is that, while the rate of motility depends strongly on the concentration of CP and Arp2/3, the net rate of actin assembly is insensitive to changes in either factor. By reorganizing their architecture, dendritic actin networks harness the same assembly kinetics to drive different rates of motility.

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Available from: R. Dyche Mullins, Jan 11, 2014
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    • "Capping protein (CP) is mandatory for symmetry breaking and motility (Iwasa & Mullins, 2007; Loisel et al., 1999). However, at the concentration used in motility assays (Achard et al., 2010; Akin & Mullins, 2008; Loisel et al., 1999; Reymann et al., 2011), which is usually 20–50 nM, CP activates spontaneous nucleation of actin monomers in solution . Indeed, CP nucleates actin by stabilizing the nuclei at their barbed end leaving them free to elongate from their pointed end (Schafer, Jennings, & Cooper, 1996). "
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    ABSTRACT: The actin cytoskeleton is a key component of the cellular architecture. However, understanding actin organization and dynamics in vivo is a complex challenge. Reconstitution of actin structures in vitro, in simplified media, allows one to pinpoint the cellular biochemical components and their molecular interactions underlying the architecture and dynamics of the actin network. Previously, little was known about the extent to which geometrical constraints influence the dynamic ultrastructure of these networks. Therefore, in order to study the balance between biochemical and geometrical control of complex actin organization, we used the innovative methodologies of UV and laser patterning to design a wide repertoire of nucleation geometries from which we assembled branched actin networks. Using these methods, we were able to reconstitute complex actin network organizations, closely related to cellular architecture, to precisely direct and control their 3D connections. This methodology mimics the actin networks encountered in cells and can serve in the fabrication of innovative bioinspired systems.
    Methods in enzymology 03/2014; 540:283-300. DOI:10.1016/B978-0-12-397924-7.00016-9 · 2.09 Impact Factor
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    • "The funneling hypothesis proposes that capping older filaments and inhibiting their growth increases the concentration of available actin monomers, leading to more rapid elongation of new uncapped filaments at the bacterial surface (Carlier et al., 1997). The monomer-gating hypothesis proposes that capping acts as a switch that gates actin monomers to the Arp2/3 complex, enhancing the rate of actin nucleation (Akin and Mullins, 2008). Resolving these hypotheses will await further experimentation. "
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    Cell host & microbe 09/2013; 14(3):242-55. DOI:10.1016/j.chom.2013.08.011 · 12.33 Impact Factor
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    • "Indeed, when capping activity is high, newly nucleated branched filaments become rapidly capped; this also causes a local increase in the concentration of available actin monomers, which further feeds Arp2/3 nucleation/ branching activity, ultimately promoting the generation of a dense and highly branched dendritic array of short actin filaments. Conversely, when capping activity is low, local monomer availability is reduced, as G-actin becomes incorporated into long and uncapped actin filaments (Mogilner and Rubinstein, 2005; Akin and Mullins, 2008; Korobova and Svitkina, 2008). "
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