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[alpha]E-catenin binds the cell--cell adhesion complex of [alpha]E-cadherin and [beta]-catenin ([beta]-cat) regulates filamentous actin (F-actin) dynamics. In vitro, binding of [alpha]E-catenin to the E-cadherin-[beta]-cat complex lowers [alpha]E-catenin affinity for F-actin, and [alpha]E-catenin alone can bind F-actin and inhibit Arp2/3 complex--mediated actin polymerization. In cells, to test whether [alpha]E-catenin regulates actin dynamics independently of the cadherin complex, the cytosolic [alpha]E-catenin pool was sequestered to mitochondria without affecting overall levels of [alpha]E-catenin or the cadherin--catenin complex. Sequestering cytosolic [alpha]E-catenin to mitochondria alters lamellipodia architecture and increases membrane dynamics and cell migration without affecting cell--cell adhesion. In contrast, sequestration of cytosolic [alpha]E-catenin to the plasma membrane reduces membrane dynamics. These results demonstrate that the cytosolic pool of [alpha]E-catenin regulates actin dynamics independently of cell--cell adhesion. doi/10.1083/jcb.200910041

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2005.09.020 Byline: Soichiro Yamada (1), Sabine Pokutta (1)(2), Frauke Drees (1), William I. Weis (1)(2), W. James Nelson (1) Abstract: Spatial and functional organization of cells in tissues is determined by cell-cell adhesion, thought to be initiated through trans-interactions between extracellular domains of the cadherin family of adhesion proteins, and strengthened by linkage to the actin cytoskeleton. Prevailing dogma is that cadherins are linked to the actin cytoskeleton through [beta]-catenin and [alpha]-catenin, although the quaternary complex has never been demonstrated. We test this hypothesis and find that [alpha]-catenin does not interact with actin filaments and the E-cadherin-[beta]-catenin complex simultaneously, even in the presence of the actin binding proteins vinculin and [alpha]-actinin, either in solution or on isolated cadherin-containing membranes. Direct analysis in polarized cells shows that mobilities of E-cadherin, [beta]-catenin, and [alpha]-catenin are similar, regardless of the dynamic state of actin assembly, whereas actin and several actin binding proteins have higher mobilities. These results suggest that the linkage between the cadherin-catenin complex and actin filaments is more dynamic than previously appreciated. Author Affiliation: (1) Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA (2) Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA Article History: Received 1 April 2005; Revised 28 July 2005; Accepted 12 September 2005 Article Note: (miscellaneous) Published: December 1, 2005

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.cell.2005.09.021 Byline: Frauke Drees (1), Sabine Pokutta (1)(2), Soichiro Yamada (1), W. James Nelson (1), William I. Weis (1)(2) Abstract: Epithelial cell-cell junctions, organized by adhesion proteins and the underlying actin cytoskeleton, are considered to be stable structures maintaining the structural integrity of tissues. Contrary to the idea that [alpha]-catenin links the adhesion protein E-cadherin through [beta]-catenin to the actin cytoskeleton, in the accompanying paper we report that [alpha]-catenin does not bind simultaneously to both E-cadherin-[beta]-catenin and actin filaments. Here we demonstrate that [alpha]-catenin exists as a monomer or a homodimer with different binding properties. Monomeric [alpha]-catenin binds more strongly to E-cadherin-[beta]-catenin, whereas the dimer preferentially binds actin filaments. Different molecular conformations are associated with these different binding states, indicating that [alpha]-catenin is an allosteric protein. Significantly, [alpha]-catenin directly regulates actin-filament organization by suppressing Arp2/3-mediated actin polymerization, likely by competing with the Arp2/3 complex for binding to actin filaments. These results indicate a new role for [alpha]-catenin in local regulation of actin assembly and organization at sites of cadherin-mediated cell-cell adhesion. Author Affiliation: (1) Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, CA 94305, USA (2) Department of Structural Biology, Stanford University School of Medicine, Stanford, CA 94305, USA Article History: Received 31 March 2005; Revised 28 July 2005; Accepted 12 September 2005 Article Note: (miscellaneous) Published: December 1, 2005

The mechanisms of calcium induced regulation were evaluated by measuring direct calcium binding to individual domains and calcium-dependent homoassociation. Results reveal that high local concentration were necessary for binding because of the cadherin molecule cluster on the cell surface. This suggests that the calcium binding pocket between domains is necessary for the interaction with alphaEbeta7.

Mutations at two sites of the EF-hand calcium binding sites are used to analyze the individual calcium-binding features of kinase from Plasmodium falciparum. Mutation at site I decreases the Ca2+ activity and at site II eliminates the kinase function. The kinase consists of an N-terminal linked to a C-terminal.

Cell-cell and cell-matrix junctions transmit mechanical forces during tissue morphogenesis and homeostasis. α-Catenin links cell-cell adhesion complexes to the actin cytoskeleton, and mechanical load strengthens its binding to F-actin in a direction-sensitive manner. Specifically, optical trap experiments revealed that force promotes a transition between weak and strong actin-bound states. Here, we describe the cryo-electron microscopy structure of the F-actinbound αE-catenin actin-binding domain, which in solution forms a five-helix bundle. In the actinbound structure, the first helix of the bundle dissociates and the remaining four helices and connecting loops rearrange to form the interface with actin. Deletion of the first helix produces strong actin binding in the absence of force, suggesting that the actin-bound structure corresponds to the strong state. Our analysis explains how mechanical force applied to aE-catenin or its homolog vinculin favors the strongly bound state, and the dependence of catch bond strength on the direction of applied force. [ABSTRACT FROM AUTHOR]

αE-catenin, an essential component of the adherens junction, interacts with the classical cadherin-β-catenin complex and with F-actin, but its precise role is unknown. αE-catenin also binds to the F-actinbinding protein vinculin, which also appears to be important in junction assembly. Vinculin and αE-catenin are homologs that contain a series of helical bundle domains, D1-D5. We mapped the vinculin-binding site to a sequence in D3a comprising the central two helices of a four-helix bundle. The crystal structure of this peptide motif bound to vinculin D1 shows that the two helices adopt a parallel, colinear arrangement suggesting that the αE-catenin D3a bundle must unfold in order to bind vinculin. We show that αE-catenin D3 binds strongly to vinculin, whereas larger fragments and full-length αE-catenin bind approximately 1,000-fold more weakly. Thus, intramolecular interactions within αE-catenin inhibit binding to vinculin. The actin-binding activity of vinculin is inhibited by an intramolecular interaction between the head (D1-D4) and the actin-binding D5 tail. In the absence of F-actin, there is no detectable binding of αE-catenin D3 to full-length vinculin; however, αE-catenin D3 promotes binding of vinculin to F-actin whereas full-length αE-catenin does not. These findings support the combinatorial or "coincidence" model of activation in which binding of high-affinity proteins to the vinculin head and tail is required to shift the conformational equilibrium of vinculin from a closed, autoinhibited state to an open, stable F-actin-binding state. The data also imply that αE-catenin must be activated in order to bind to vinculin. [ABSTRACT FROM AUTHOR]

Cadherins are transmembrane adhesion molecules that mediate homotypic cell-cell contact. In adherens junctions, the cytoplasmic domain of cadherins is functionally linked to the actin cytoskeleton through a series of proteins known as catenins. E-cadherin binds to beta-catenin, which in turn binds to alpha-catenin to form a ternary complex. alpha-Catenin also binds to actin, and it was assumed previously that alpha-catenin links the cadherin-catenin complex to actin. However, biochemical, structural and live-cell imaging studies of the cadherin-catenin complex and its interaction with actin show that binding of beta-catenin to alpha-catenin prevents the latter from binding to actin. Biochemical and structural data indicate that alpha-catenin acts as an allosteric protein whose conformation and activity changes depending on whether or not it is bound to beta-catenin. Initial contacts between cells occur on dynamic lamellipodia formed by polymerization of branched actin networks, a process controlled by the Arp2/3 (actin-related protein 2/3) complex. alpha-Catenin can suppress the activity of Arp2/3 by competing for actin filaments. These findings lead to a model for adherens junction formation in which clustering of the cadherin-beta-catenin complex recruits high levels of alpha-catenin that can suppress the Arp2/3 complex, leading to cessation of lamellipodial movement and formation of a stable contact. Thus alpha-catenin appears to play a central role in cell-cell contact formation.