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J. Cell Biol.,
Volume 144, Number 6, March 22, 1999 1245-1258




* Dynamique du Cytosquelette, Laboratoire d'Enzymologie et Biochimie Structurales, CNRS, 91198 Gif-sur-Yvette, France; § Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139; Intracellular propulsion of Listeria monocytogenes is the best understood form of motility dependent on actin polymerization. We have used in vitro
motility assays of Listeria in platelet and brain extracts
to elucidate the function of the focal adhesion proteins
of the Ena (Drosophila Enabled)/VASP (vasodilator-stimulated phosphoprotein) family in actin-based motility. Immunodepletion of VASP from platelet extracts
and of Evl (Ena/VASP-like protein) from brain extracts
of Mena knockout (
Cell Biology,
Zoological Institute, Technical University, 38092 Braunschweig, Germany; and
National Research Center for
Biotechnology, 38124 Braunschweig, Germany
/
) mice combined with add-back of recombinant (bacterial or eukaryotic) VASP
and Evl show that VASP, Mena, and Evl play interchangeable roles and are required to transform actin
polymerization into active movement and propulsive
force. The EVH1 (Ena/VASP homology 1) domain of VASP is in slow association-dissociation equilibrium
high-affinity binding to the zyxin-homologous, proline-rich region of ActA. VASP also interacts with F-actin
via its COOH-terminal EVH2 domain. Hence VASP/
Ena/Evl link the bacterium to the actin tail, which is required for movement. The affinity of VASP for F-actin
is controlled by phosphorylation of serine 157 by
cAMP-dependent protein kinase. Phospho-VASP binds
with high affinity (0.5 × 108 M
1); dephospho-VASP
binds 40-fold less tightly. We propose a molecular ratchet model for insertional polymerization of actin,
within which frequent attachment-detachment of
VASP to F-actin allows its sliding along the growing filament.
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