AN INTRAMOLECULAR ASSOCIATION BETWEEN THE HEAD AND TAIL DOMAINS OF VINCULIN MODULATES TALIN BINDING

Three independent lines of evidence demonstrate an interaction between the head and tail domains of vinculin. First, both the purified 30-kD a tail fragment and a fusion protein containing tail domain, vinculin residues 884-1066, protect purified 95-kDa head domain from cleavage b y protease V8 in a specific, dose dependent manner. Second, direct bin ding studies between the 95-kDa head and the V884-1066 fusion protein and carboxyl-terminal truncations of the fusion protein indicate a tig ht interaction (K-d similar to 50 nM) that requires vinculin residues 1013-1043. Finally, cross-linking of vinculin demonstrates cross-linka ble head tail complexes in the intact protein, which are almost exclus ively intramolecular. Talin and the tail domain compete for binding to the vinculin head domain. Therefore, we propose that the loss of the intramolecular interaction of head and tail accounts for the increased affinity for talin of the head domain compared with intact vinculin. The observation that a head-tail interaction in the molecule affects t he ability of vinculin to interact with another adherens junction comp onent suggests that modulation of head-tail binding is a way to contro l recruitment of vinculin into an adherens junction.