Cadherins are calcium-dependent cell adhesion proteins that play an important role in normal development. This family of glycoproteins is responsible for cell-cell adhesion. They preferentially interact with themselves in a homophilic manner to connect cells, thus, they act as both the receptor and the ligand. Structurally, cadherins usually consist of 5 tandemly repeated extracellular domains, 1 membrane-spanning region, and a cytoplasmic region. The N-terminal extracellular domains regulate cell-cell contact. These proteins require calcium in order to function. Lack of calcium deters their adhesive activity and makes cadherins vulnerable to proteases.
This particular epithelial type of cadherin, or E-cadherin, is found in non-neural epithelial tissues. The two N-terminal repeats of the 5 domain extracellular region are shown here. It exists as a dimer, with each monomer consisting of 226 amino acid residues. Each monomer binds 3 calcium (Ca2+) ions (green) and 1 mercury (Hg2+) ion (blue). The binding of the calcium ions not only linearizes and rigidifies the molecule, it also induces the dimerization process.