MOLECULAR-ORGANIZATION OF THE DESMOGLEIN-PLAKOGLOBIN COMPLEX

Different epithelial intercellular junctions contain distinct complexe s incorporating plakoglobin, In adherens junctions, plakoglohin intera cts with two molecules, the transmembrane adhesion protein of the cadh erin family (e.g. E-cadherin) and alpha-catenin, The latter is thought to anchor the cadherin-plakoglobin complex to the cortical actin cyto skeleton, In desmosomes, plakoglobin forms a complex with desmosomal c adherins, either desmoglein (Dsg) or desmocollin (Dsc), but not with a lpha-catenin, To further understand the structure and assembly of the plakoglobin-cadherin complexes we analyzed amino acid residues involve d in plakoglobin-Dsg interactions using alanine scanning mutagenesis. Previously, we have shown that plakoglobin interacts with a 72 amino a cid-long cytoplasmic domain (C-domain) that is conserved among desmoso mal and classic cadherins, In this paper, we show that a row of the la rge hydrophobic residues located at the C-terminal portion of the Dsg C-domain is indispensable for interaction with plakoglobin. To study a reciprocal site we expressed plakoglobin (MPg) or its mutants tagged by 6 myc epitope in epithelial A-431 cells, Using sucrose gradient cen trifugation and subsequent coimmunoprecipitation, MPg was found to be efficiently incorporated into the same type of complexes as endogenous plakoglobin, A major pool of Dsg-plakoglobin complexes sedimented at 8S and exhibited a 1:1 stoichiometry, Using alanine scanning mutagenes is and the co-immunoprecipitation assay we identified nine hydrophobic amino acids within the arm repeats 1-3 of plakoglobin, that are requi red for binding to Dsg and Dsc, Eight of these amino acids also partic ipate in the interaction with a-catenin, No mutations were found to re duce the affinity of plakoglobin binding to E-cadherin, These data pro vide direct evidence that the same hydrophobic plakoglobin surface is essential for mutually exclusive interaction with distinct proteins su ch as alpha-catenin and desmosomal cadherins.