The EVH2 Domain of the Vasodilator-stimulated Phosphoprotein Mediates Tetramerization, F-actin Binding, and Actin Bundle Formation

Vasodilator-stimulated phosphoprotein (VASP) is a member of the Ena/VASP family of proteins that are implicated in regulation of the actin cytoskeleton. All family members share a tripartite structural organization, comprising an N-terminal Ena/VASP homology (EVH) 1 domain, a more divergent proline-rich central part, and a common C-terminal EVH2 region of about 160-190 amino acids. Using chemical cross-linking, sucrose gradient sedimentation, and gel filtration analyses of different truncated VASP constructs, we demonstrate that the VASP EVH2 region is both necessary and sufficient for tetramerization. Moreover, co-sedimentation and fluorescent phalloidin staining showed that the EVH2 region binds and bundles F-actin in vitro and localizes to stress fibers in transfected cells. Analysis of the functional contribution of highly conserved blocks within this region indicated that residues 259-276 of human VASP are essential for the interaction with F-actin, whereas residues 343-380 are required for tetramerization, probably via coiled-coil formation. Interactions with F-actin are enhanced by VASP tetramerization. The results demonstrate that the C-terminal EVH2 segment is not only conserved in sequence but also forms a distinct functional entity. The data suggest that the EVH2 segment represents a novel oligomerization and F-actin binding domain.