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

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