Eph - Ephrin interaction

Ephrin and Ephrin receptor (Eph) are both membrane proteins for cell-cell interaction. In the nervous system, they work for axonal guidance and usually Eph activation is a signal for repulsion. Both EphA and EphB have a cytoplasmic tyrosine kinase domain. Ephrin A is tethered to the plasma membrane by a GPI anchor, while Ephrin B has a transmembrane region and interacts with some scaffolding proteins at the cytoplasm. They interact with each other to form a 2:2 heterotetramer. The whole ectodomain structure of EphA suggests that the dimeric interaction of the cytoplasmic kinase domains between a pair of Eph in the 2:2 complex is unlikely, because the ectodomain swings out from each other significantly around the transmembrane region.