title: αE-catenin is an autoinhibited molecule that coactivates vinculin.
abstract: 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-actin-binding 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.
authors.affiliation: Department of Structural Biology, Stanford University School of Medicine, 299 Campus Drive, Stanford, CA 94305, USA.
authors.forename: Hee-Jung
authors.initials: HJ
authors.lastname: Choi
authors.forename: Sabine
authors.initials: S
authors.lastname: Pokutta
authors.forename: Gregory W
authors.initials: GW
authors.lastname: Cadwell
authors.forename: Andrey A
authors.initials: AA
authors.lastname: Bobkov
authors.forename: Laurie A
authors.initials: LA
authors.lastname: Bankston
authors.forename: Robert C
authors.initials: RC
authors.lastname: Liddington
authors.forename: William I
authors.initials: WI
authors.lastname: Weis
mesh_terms: D000199:Actins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites / Q000235:genetics; D015820:Cadherins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D002151:Calorimetry / Q000379:methods; D002645:Chickens; D002942:Circular Dichroism; D018360:Crystallography, X-Ray; D051379:Mice; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009154:Mutation; D011485:Protein Binding; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011993:Recombinant Fusion Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D016596:Vinculin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051178:alpha Catenin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D051176:beta Catenin / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D015820:Cadherins; D011993:Recombinant Fusion Proteins; D051178:alpha Catenin; D051176:beta Catenin; D016596:Vinculin