Diffusion of the disordered E-cadherin tail on β-catenin

Specific protein interactions typically require well-shaped binding interfaces. Here, we report a cunning exception. The disordered tail of the cell-adhesion protein E-cadherin dynamically samples a large surface area of the proto-oncogene {beta}-catenin. Single-molecule experiments and molecular simulations resolve these motions with high resolution in space and time. Contacts break and form within hundreds of microseconds without dissociation of the complex. A few persistent interactions provide specificity whereas unspecific contacts boost affinity. The energy landscape of this complex is rugged with many small barriers (3 - 4 kBT) and reconciles specificity, high affinity, and extreme disorder. Given the roles of {beta}-catenin in cell-adhesion, signalling, and cancer, this Velcro-like design has the potential to tune the stability of the complex without requiring dissociation.