Without E-cadherins, tumor cells will have much easier time invading into other tissues. Structure E-CAD1 contains seven beta sheets and two very short alpha helices. The two regions are 20 A apart from each other. Metal-binding pocket is composed of DAD sequence, where the glutamate residues provide the negative charge for binding positively charged calcium ions. Homophilic specificity-conferring surface is made up of HAV motif starting at residue number 79.
Additional residues seem to participate in the homophilic specificity as well.
However, there are enough differences to keep them as a separate family. First, the disulfide bond commonly found in Ig family is not found in E-cad. Second, E-CAD1 forms many hydrogen bonds between beta sheets to form a beta barrel, where as Ig family does not. Third, the metal binding pocket of E-CAD1 is not present in Ig family. Ikura M. Solution structure of the epithelial cadherin domain reponsible for selective cell adhesion.