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

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