(A) Binding of Vt to RRM1-3 (ΔH, -10.5±0.2 kcal/mol; ΔS, -12.9 cal/mol) as determined by ITC. Representative analyses are shown. The K_d of the interactions is provided in the lower inset. N represents the stoichiometry of the binding reactions.
(B) Binding of Vt to RRM1 (ΔH, -15.1±0.5 kcal/mol; ΔS, -29.7 cal/mol).
(C) Binding of Vt to RRM2-RRM3.
(D), (E) Mutations of raver1 predicted to disrupt electrostatic interactions with vinculin. Glu120Lys (D) or Arg121Glu (E) substitution mutations abolish binding to Vt. Binding of raver1 mutant E120K was also not detected by size exclusion chromatography (data not shown).

HeLa cells were transfected with p3xFLAG-CMV-7.1 alone (Vector) or with this vector expressing raver1 RRM1-3 or RRM1-3 (E120K). After 48 hours, cells were stained with anti-Flag antibody (green, left) and anti-vinculin antibody (red, center). The co-localization of vinculin and raver1 RRM1-3 (white arrows) is seen as yellow (right) from superposition of green and red channels. By contrast, raver1 RRM1-3 (E120K) is predominately nuclear and does not co-localize with endogenous vinculin.

While raver1 does not bind F-actin, the Vt:raver1 complex co-sediments with F-actin. After F-actin co-sedimentation, supernatants (S) were removed and pellets (P, having polymerized F-actin) were washed twice.

Domain Organization of human Vinculin (top) and human Raver1 (bottom). Vinculin domains Vh1, Vh2, Vh3, and Vt2 together comprise the vinculin head domain VH. NES, nuclear export sequence; NLS, nuclear localization signal.

(A) The Vt:RRM1-3 complex structure is shown in ribbon representation with the five α-helices (H1-H5) of the tail domain of human vinculin in green, the N-terminal helix of raver1 in gray, RRM1 in blue, RRM2 in yellow, and RRM3 in red. Left, head-on view, and right, rotated by 90°, showing the interaction of the loops connecting the β3-β2, β1-α1, and β4-β5 strands of raver1 with H2 and H3 α-helices of vinculin's tail domain.
(B) The Vt:RRM1 structure showing the β-sheets and α-helices of RRM1 in purple and light blue, respectively. Residues involved in the Vt-RRM1 interaction are shown on the right panel. The intermolecular hydrogen-bonding network is indicated by dotted lines. The side chain atoms, NE and NH2 of raver1-Arg121 engage in electrostatic interactions with vinculin-Glu932 atoms OE1 and OE2, respectively, while raver1-Arg121 (NH1) is held in place through interactions with the main chain oxygen of raver1-Arg119 as well as OD2 of vinculin-Asp953. An additional electrostatic interaction was also found between side chains of raver1-Glu120 and vinculin-Arg945, which spatially orients the side chain of vinculin-Arg945 such that it is parallel to the side chain of raver1-Arg117 and provides a stable surface for hydrophobic interaction.

(A) Superposition of the Vt:RRM1-3 complex (color coding is the same as in Figure 3) with full-length, inactive human vinculin (shown in pink). The raver1 binding site is occluded by the 882-890 loop region of inactive vinculin. Asp882 of Vt in its raver1 bound state is indicated as well as Pro877 of inactive vinculin (dashed arrows).
(B) Interaction with vinculin alters the structure of the binding loops of raver1. Superposition of the native mouse RRM1 domain (PDBID 1WI6, yellow) onto human RRM1 (blue) when bound to vinculin (green). Upon binding to vinculin, β-strand β4 moves as indicated by red arrows. In the unbound raver1 structure, only two interactions are found between the β-hairpin and the loop region situated between strand β1 and helix α1 (Arg127 and Asp77 as well as Arg129 and Leu74; not shown for clarity). However, in the Vt:raver1 complex the side chain of Arg121 interacts with main chain oxygen of Arg119; the side chain of Arg119 engages in electrostatic interactions with the side chains of Asp69 and Glu74; and the side chain of Arg117 is in contact with the main chain oxygen of Glu120. The hydrophobic cavity observed on the surface near the β-hairpin is rather large in the unbound conformation, which almost completely disappears in the complex.

The activation of vinculin (blue), by talin and perhaps other signals (Izard et al., 2004; Weis, 2004; del Rio et al., 2009), following the engagement of integrin receptors (α and β subunits) provokes alterations in the structure of its head (VH) domain that disrupt the head-tail interaction that holds vinculin in its inactive conformation. Activated vinculin then binds to the RRM1 domain of raver1 (red) through the agency of its tail (Vt) domain. This interaction is permissive for the interactions of the three tandem RRM domains of raver1 with their mRNA cargo (combs), which might include vinculin mRNA and transcripts encoding other components of adhesion complexes. The vinculin-raver1 interaction is also permissive for binding to actin filaments (white spheres). This feed-forward delivery system would ensure rapid and coordinated production of components of adhesion complexes by the translational machinery at these adhesion microcompartments, as seen in vivo (Chicurel et al., 1998; Rodriguez et al., 2006).