Ephrin Receptor - Subclasses

Subclasses

Ephs can be divided into two subclasses, EphAs and EphBs (encoded by the genetic loci designated EPHA and EPHB respectively), based on sequence similarity and on their binding affinity for either the glycosylphosphatidylinositol-linked ephrin-A ligands or the transmembrane-bound ephrin-B ligands. Of the 16 Eph receptors (see above) that have been identified in animals, humans are known to express nine EphAs (EphA1-8 and EphA10) and five EphBs (EphB1-4 and EphB6). In general, Ephs of a particular subclass bind preferentially to all ephrins of the corresponding sublcass, but have little to no cross-binding to ephrins of the opposing subclass. It has recently been proposed that the intrasubclass specificity of Eph/ephrin binding could be partially attributed to the different binding mechanisms used by EphAs and EphBs. There are exceptions to the intrasubclass binding specificity observed in Ephs, however, as it has recently been shown that ephrin-B3 can bind to and activate EphA4 and that ephrin-A5 can bind to and activate EphB2. EphA/ephrinA interaction typically occur with higher affinity than EphB/ephrin-B interactions which can partially be attributed to the fact that ephrin-As bind via a "lock-and-key" mechanism that requires little conformational change of the EphAs in contrast to EphBs which utilize an "induced fit" mechanism that requires a greater amount of energy to alter the conformation of EphBs to bind to ephrin-Bs.

16 Ephs have been identified in animals and are listed below:

• EPHA1, EPHA2, EPHA3, EPHA4, EPHA5, EPHA6, EPHA7, EPHA8, EPHA9, EPHA10
• EPHB1, EPHB2, EPHB3, EPHB4, EPHB5, EPHB6