A mathematical model of alpha-catenin dimerization at adherens junctions in polarized epithelial cells.

The protein alpha-catenin is found as a monomer or homodimer. As a monomer, alpha-catenin can bind to beta-catenin, which localizes to the plasma membrane at the site of adherens junctions (AJs) in polarized epithelial cells. As a dimer, alpha-catenin can bind to actin filaments, affecting the organization of the actin cytoskeleton. At usual cytoplasmic concentrations, alpha-catenin is found predominantly in monomeric form. It is currently thought that alpha-catenin cannot simultaneously bind beta-catenin and homodimerize, and that the dynamics of binding and unbinding from beta-catenin, possibly coupled with lower diffusion near an AJ, are sufficient to locally accumulate alpha-catenin monomers and homodimers. Using a mathematical model of alpha-catenin dynamics, I show that alpha-catenin must transiently homodimerize while bound to beta-catenin in order for homodimers to form, even in the presence of a spatial diffusion gradient.