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.