E-Cadherin Functions As A Desmoglein Transporter That Facilitates Assembly Of Nascent Desmosomes

Desmosomes are robust adhesive junctions found in tissues that resist mechanical stress. Their intercellular region is composed of densely packed desmocollin (Dsc) and desmoglein (Dsg) adhesive proteins. Previous studies demonstrated that E-cadherin (Ecad), an essential cell-cell adhesion protein, is required for the initial assembly of desmosomes. However, the mechanistic role of Ecad in desmosome formation is unknown. Here, we use single molecule force measurements with an atomic force microscope (AFM), super resolution imaging, and protein docking computations, to resolve the roles of Ecad and isoform 2 of Dsc and Dsg in the desmosome assembly process. AFM force measurements reveal that Ecad forms short-lived interactions with Dsg2 but does not bind to Dsc2. Force measurements with Ecad mutants and protein docking demonstrate that Ecad and Dsg2 bind in a novel trans-conformation mediated by the conserved Leu 175 on the Ecad ectodomain. Single molecule AFM measurements also show that Dsc2 forms long-lived bonds with Dsg2, but interacts only weakly with Dsc2. Taken together, this data suggests that while Ecad and Dsg2 from opposing cells interact and facilitate desmosome assembly, Dsg2 subsequently dissociates from Ecad and binds to Dsc2 to mediate robust adhesion in mature desmosomes. We confirm this using super resolution imaging of desmosomes in human keratinocytes and show that while Ecad is localized to nascent desmosomes, it is excluded as the desmosomes mature.