Eph receptors are the largest family of receptor tyrosine kinases (RTKs). EphA receptors (EphA1-10) bind ephrinA ligands which are GPI-linked proteins and EphB receptors (EphB1-6) bind ephrinB ligands which are membrane protein with one transmembrane domain. Within each subfamily, interactions between receptor and ligand are promiscuous. In addition, Eph receptors can also bind ephrins from the other class. Forward and reverse signaling through Eph receptors is a unique characteristic to this RTK since ephrins are physically linked to the plasma membrane.