Mediates calcium-dependent cell-cell adhesion during the early stage of development. Associated with the ecto-surface of the plasma membrane. May be transported to the plasma membrane via contractile vacuoles and its cell surface association may be mediated by an integral membrane protein. Expressed soon after the initiation of development. Expression is controlled by rpkA. Cell binding activity is dependent on the N-terminal segment whereas the C-terminal domain tethers the protein to the cell membrane. The N-terminus is blocked. Belongs to the Dictyostelium CAD family.