Ephrin-B1, also named EFL-3, ELK ligand, EPH-related receptor tyrosine kinase ligand 2, is a single-pass type I membrane protein. It contains 1 ephrin RBD (ephrin receptor-binding) domain and belongs to the ephrin family. Ephrins are divided into the ephrin-A (EFNA) class, which are anchored to the membrane by a glycosylphosphatidylinositol linkage, and the ephrin-B (EFNB) class, which are transmembrane proteins. All ephrins share a conserved extracellular sequence, which most likely corresponds to the receptor-binding domain. Ephrin-B1 has been shown to bind EphA3, EphB1, EphB2, EphB3, and EphB4. The extracellular domains of human and mouse ephrin-B1 share 94% amino acid identity.