sentences:  Ephrin ligands are divided into two subclasses of ephrin-A and ephrin-B based on their structure and linkage to the cell membrane.Ephrin-As are anchored to the membrane by a glycosylphosphatidylinositol (GPI) linkage and lack a cytoplasmic domain, while ephrin-Bs are attached to the membrane by a single transmembrane domain that contains a short cytoplasmic PDZ-binding motif.The genes that encode the ephrin-A and ephrin-B proteins are designated as "EFNA" and "EFNB" respectively.