Figure 1:

Metavinculin tail (MVt) domain exhibits similar F-actin binding affinity but dramatically reduced bundling (crosslinking) of the filaments relative to the vinculin tail (Vt) domain. (A) Schematic representation of Vt and MVt constructs used in this study. Vt consists of five α-helices (H1–H5) flanked by an N-terminal strap (NtS) and a C-terminal hairpin (CtHP). MVt contains a 68-residue insert between helices H1 and H2 that replaces the original H1 and NtS by H1’ and NtS’. MVtp includes the 21-residue proline-rich linker preceding the NtS of MVt. Mutations within the metavinculin insert region, namely A934V, ΔL954 and R975W, have been identified in cardiomyopathies. (B) X-ray crystal structures of Vt (PDB ID 1TR2) and MVt (PDB ID 3MYI) as well as the cryo-EM reconstruction of Vt-actin (EMD-6446) and MVt-actin (EMD-6447) interfaces. Vt and MVt are comprised of a highly similar 5-helix bundle fold in the absence of actin, where H1’ of MVt swaps with H1 of Vt. Upon actin engagement, regions N-terminal of H2 are not detectable in the cryo-EM reconstructions. (C) Negative stain EM images of actin filaments. Micrographs are acquired at the same magnification (scale bar = 500 nm, shown in the left panel). Crosslinking or bundling of actin filaments by Vt generates thick fibers. In contrast, MVt and MVtp do not promote actin filament bundling.