ASSEMBLY OF THE CADHERIN CATENIN COMPLEX IN-VITRO WITH RECOMBINANT PROTEINS

The cytoplasmic domain of classical cadherins is tightly associated wi th three proteins termed alpha-, beta- and gamma-catenin. These access ory proteins are of central importance for the adhesive properties of this class of cell adhesion molecules. In order to examine the molecul ar architecture of the cadherin-catenin complex in more detail we have expressed the catenins and the cytoplasmic domain of E-cadherin as fu sion proteins in Escherichia coli, and analyzed the interaction of pur ified recombinant cadherin and catenins in combinatorial protein-prote in interaction experiments. The cytoplasmic domain of E-cadherin canno t directly associate with alpha-catenin but interacts with high affini ty with beta-catenin, whereas the binding of gamma-catenin (plakoglo-b in) to E-cadherin is less efficient, alpha- and beta-catenin assemble into a 1:1 heterodimeric complex. The analysis of various truncated be ta-catenins revealed that an alpha-catenin binding site in beta-cateni n is localized between amino acid positions 120 and 151. The central r ole of beta-catenin for the assembly of the heterotrimeric E-cadherin/ alpha-catenin/beta-catenin complex in mixing experiments with all comp onents was demonstrated. The reconstitution in vitro of the cadherin-c atenin complex should allow the study of the interaction with signalli ng molecules and with the actin-based cytoskeleton.