Force-dependent allostery of the α-catenin actin-binding domain controls adherens junction dynamics and functions

Abstract

α-catenin is a key mechanosensor that forms force-dependent interactions with F-actin, thereby coupling the cadherin-catenin complex to the actin cytoskeleton at adherens junctions (AJs). However, the molecular mechanisms by which α-catenin engages F-actin under tension remained elusive. Here we show that the α1-helix of the α-catenin actin-binding domain (αcat-ABD) is a mechanosensing motif that regulates tension-dependent F-actin binding and bundling. αcat-ABD containing an α1-helix-unfolding mutation (H1) shows enhanced binding to F-actin in vitro. Although full-length α-catenin-H1 can generate epithelial monolayers that resist mechanical disruption, it fails to support normal AJ regulation in vivo. Structural and simulation analyses suggest that α1-helix allosterically controls the actin-binding residue V796 dynamics. Crystal structures of αcat-ABD-H1 homodimer suggest that α-catenin can facilitate actin bundling while it remains bound to E-cadherin. We propose that force-dependent allosteric regulation of αcat-ABD promotes dynamic interactions with F-actin involved in actin bundling, cadherin clustering, and AJ remodeling during tissue morphogenesis.

In vivo optochemical control of cell contractility at single‐cell resolution

“…One expects that a contracting cell applies a force on the junctional complexes linking it to its neighbors within the epithelium (Fig A). To assess this action, we employed a reporter for tension across adherens junctions, based on the force‐dependent conformational state of α‐Catenin . α‐Catenin exhibits a force‐dependent switch between two stable conformations.…”

“…Firstly, we applied a Vinculin‐derived reporter, which preferentially binds to the open conformation of α‐Catenin. α‐Catenin undergoes a force‐dependent conformational change, which opens a Vinculin binding site under mechanical pull . Secondly, we directly assayed junctional tension in neighboring cells by measuring the initial recoil velocity after ablation.…”

Role of α-Catenin and its mechanosensing properties in the regulation of Hippo/YAP-dependent tissue growth

“…We took advantage of the Yki-dependent increase in adult wing size upon α-Cat overexpression to assess the function of different α-Cat domains in tissue growth. For these tests we used constructs we published previously [Sarpal et al, 2012;Desai et al, 2013;Ishiyama et al, 2018] and a new set of constructs that were rendered resistant to α-Cat-RNAi(1) and α-Cat-RNAi(2) and will be designated as α-CatR-XX. Both α-Cat and α-CatR encode wildtype proteins.…”

“…α-catenin can also act as a mechanosensor. Biochemical responses to mechanosensing are thought to have multiple consequences [Pinhero and Bellaiche, 2018;Charras and Yap, 2018;Yap et al, 2018], including a strengthening of F-actin binding to enhance cell adhesion [Yonemura et al, 2010;Buckley et al, 2014;Ishiyama et al, 2013;2018], reorganization of actin at cell junctions [Ishiyama et al, 2018], and modulation of cell signalling that regulates tissue growth through the Hippo/YAP pathway [Rauskolb et al, 2014]. However, in vivo evidence for specific functions of α-catenin-mediated mechanosensing remains very limited.…”

“…The α-catenin protein comprises three evolutionary conserved regions: a N-terminal region that binds to β-catenin, a central Mregion, and a C-terminal actin-binding domain (ABD). The activity of cytoplasmic myosin II applies tension to α-catenin when bound to β-catenin and F-actin, causing at least two conformational changes: First, the N-terminal α-helix within the ABD (α1-helix) is pulled away from ABD revealing an enhanced F-actin binding interface and facilitating dimerization of ABD to promote actin bundling [Ishiyama et al, 2018]. This mechanosensory property of α-catenin ABD explains its catch bond behavior, the ability of a chemical bond to strengthen as a result of force application [Buckley et al, 2014].…”