Single Amino Acid Substitutions in Proteins of the armadillo Gene Family Abolish Their Binding to -Catenin

Abstract Analysis of the calcium-dependent cell adhesion molecule E-cadherin has led to the identification of catenins, which are necessary for cadherin function. Growing evidence that cadherins and catenins are subjected to genetic alterations in carcinogenesis makes it especially important to understand protein-protein interactions within the cadherin-catenin complex. Here we report the identification and analysis of the α-catenin binding site in plakoglobin (-catenin). Using N- and C-terminal truncations of plakoglobin, we identified a domain of 29 amino acids necessary and sufficient for binding α-catenin. The α-catenin binding site is fully encoded within exon 3 of plakoglobin but only partially represented in Armadillo repeat 1. This suggests that exons rather than individual Arm repeats encode functional domains of plakoglobin. Site-directed mutagenesis identified residues in the α-catenin binding site indispensable for binding in vitro. Analogous mutations in β-catenin and Armadillo had identical effects. Our results indicate that single amino acid mutations in the α-catenin binding site of homologs of Armadillo could prevent a stable association with α-catenin, thus affecting cadherin-mediated adhesion.