SINGLE AMINO-ACID SUBSTITUTIONS IN PROTEINS OF THE ARMADILLO GENE FAMILY ABOLISH THEIR BINDING TO ALPHA-CATENIN

Analysis of the calcium-dependent cell adhesion molecule E-cadherin ha s led to the identification of catenins, which are necessary for cadhe rin function. Growing evidence that cadherins and catenins are subject ed to genetic alterations in carcinogenesis makes it especially import ant to understand protein-protein interactions within the cadherin-cat enin complex, Here we report the identification and analysis of the al pha-catenin binding site in plakoglobin (gamma-catenin). Using N- and C-terminal truncations of plakoglobin, we identified a domain of 29 am ino acids necessary and sufficient for binding alpha-catenin. The alph a-catenin binding site is fully encoded within exon 3 of plakoglobin b ut only partially represented in Armadillo repeat 1. This suggests tha t exons rather than individual Arm repeats encode functional domains o f plakoglobin. Site-directed mutagene sis identified residues in the a lpha-catenin binding site indispensable for binding in vitro, Analogou s mutations in beta-catenin and Armadillo had identical effects, Our r e suits indicate that single amino acid mutations in the alpha-catenin binding site of homologs of Armadillo could prevent a stable associat ion with alpha-catenin, thus affecting cadherin-mediated adhesion.