The Cryogenic Electron Microscopy Structure of the Cell Adhesion Regulator Metavinculin Reveals an Isoform-Specific Kinked Helix in Its Cytoskeleton Binding Domain

Abstract

Vinculin and its heart-specific splice variant metavinculin are key regulators of cell adhesion processes. These membrane-bound cytoskeletal proteins regulate the cell shape by binding to several other proteins at cell–cell and cell–matrix junctions. Vinculin and metavinculin link integrin adhesion molecules to the filamentous actin network. Loss of both proteins prevents cell adhesion and cell spreading and reduces the formation of stress fibers, focal adhesions, or lamellipodia extensions. The binding of talin at cell–matrix junctions or of α-catenin at cell–cell junctions activates vinculin and metavinculin by releasing their autoinhibitory head–tail interaction. Once activated, vinculin and metavinculin bind F-actin via their five-helix bundle tail domains. Unlike vinculin, metavinculin has a 68-amino-acid insertion before the second α-helix of this five-helix F-actin–binding domain. Here, we present the full-length cryogenic electron microscopy structure of metavinculin that captures the dynamics of its individual domains and unveiled a hallmark structural feature, namely a kinked isoform-specific α-helix in its F-actin-binding domain. Our identified conformational landscape of metavinculin suggests a structural priming mechanism that is consistent with the cell adhesion functions of metavinculin in response to mechanical and cellular cues. Our findings expand our understanding of metavinculin function in the heart with implications for the etiologies of cardiomyopathies.

Distinct inter-domain interactions of dimeric versus monomeric α-catenin link cell junctions to filaments

“…Superposition of the actin subunits of αcatenin bound and unbound actin displays a root mean square deviation of 0.7 Å for 2888 atoms. The smallest and most flexible of the four actin domains harbors the so-called D-loop, for DNase I binding loop (residues [40][41][42][43][44][45][46][47][48][49][50][51]. This loop changes its conformation upon adenosine triphosphate hydrolysis and mediates longitudinal actin-actin interactions 41,42 .…”

“…However, vinculin is monomeric and does not dimerize. In contrast to α-catenin, vinculin has its FABD buried and autoinhibited [46][47][48][49] . The nanomolar affinity of the vinculin FABD with the vinculin amino-terminal domain correlates with the large buried surface area of the vinculin FABD of about 1800 Å 2 .…”

Metavinculin mediates differentiation cues into myogenic gene expression

“…54 Several proteins activate vinculin by disrupting its auto-inhibitory head and tail interaction and metavinculin forms heterodimer with activated vinculin. 44,[54][55][56][57] Upon activation vinculin binds with actin filaments (F-actin), facilitating vinculin dimerization for its bundling. Conversely, metavinculin binding to F-actin inhibits vinculin dimerization, thereby preventing actin bundling.…”