Biochemical and structural definition of the l-afadin- and actin-binding sites of alpha-catenin.
alpha-Catenin is an integral component of adherens junctions, where it links cadherins to the actin cytoskeleton. alpha-Catenin is also required for the colocalization of the nectin/afadin/ponsin adhesion system to adherens junctions, and it specifically associates with the nectin-binding protein afadin. A proteolytic fragment of alpha-catenin, residues 385-651, contains the afadin-binding site. The three-dimensional structure of this fragment comprises two side-by-side four-helix bundles, both of which are required for afadin binding. The alpha-catenin fragment 385-651 binds afadin more strongly than the full-length protein, suggesting that the full-length protein harbors a cryptic binding site for afadin. Comparison of the alpha-catenin 385-651 structure with the recently solved structure of the alpha-catenin M-fragment (Yang, J., Dokurno, P., Tonks, N. K., and Barford, D. (2001) EMBO J. 20, 3645-3656) reveals a surprising flexibility in the orientation of the two four-helix bundles. alpha-Catenin and the actin-binding protein vinculin share sequence and most likely structural similarity within their actin-binding domains. Despite this homology, actin binding requires additional sequences adjacent to this region.
Pokutta
Sabine
S
Department of Structural Biology, Stanford University School of Medicine, Stanford, California 94305, USA.
Drees
Frauke
F
Takai
Yoshimi
Y
Nelson
W James
WJ
Weis
William I
WI
D000199:Actins / Q000378:metabolism*; D000818:Animals; D001665:Binding Sites; D001704:Biopolymers; D002460:Cell Line; D003598:Cytoskeletal Proteins / Q000737:chemistry / Q000378:metabolism*; D004285:Dogs; D008840:Microfilament Proteins / Q000378:metabolism*; D008958:Models, Molecular; D011487:Protein Conformation; D016596:Vinculin / Q000378:metabolism; D051178:alpha Catenin
D000199:Actins; D001704:Biopolymers; D003598:Cytoskeletal Proteins; D008840:Microfilament Proteins; C108835:afadin; D051178:alpha Catenin; D016596:Vinculin