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J Cell Biol. 2010 Nov 1;191(3):571-84. doi: 10.1083/jcb.201003014.

VASP is a processive actin polymerase that requires monomeric actin for barbed end association.

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1
Department of Cellular and Molecular Pharmacology, University of California, San Francisco School of Medicine, San Francisco, CA 94158, USA.

Abstract

Ena/VASP proteins regulate the actin cytoskeleton during cell migration and morphogenesis and promote assembly of both filopodial and lamellipodial actin networks. To understand the molecular mechanisms underlying their cellular functions we used total internal reflection fluorescence microscopy to visualize VASP tetramers interacting with static and growing actin filaments in vitro. We observed multiple filament binding modes: (1) static side binding, (2) side binding with one-dimensional diffusion, and (3) processive barbed end tracking. Actin monomers antagonize side binding but promote high affinity (K(d) = 9 nM) barbed end attachment. In low ionic strength buffers, VASP tetramers are weakly processive (K(off) = 0.69 s(-1)) polymerases that deliver multiple actin monomers per barbed end-binding event and effectively antagonize filament capping. In higher ionic strength buffers, VASP requires profilin for effective polymerase and anti-capping activity. Based on our observations, we propose a mechanism that accounts for all three binding modes and provides a model for how VASP promotes actin filament assembly.

PMID:
21041447
PMCID:
PMC3003327
DOI:
10.1083/jcb.201003014
[Indexed for MEDLINE]
Free PMC Article
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