Plexin A1 is a 200 kDa type I transmembrane member of the Plexin family of Semaphorin signal transducers. It consists of a 1218 amino acid (aa) extracellular domain with one Sema domain, a spacer, and four tandem IPT/TIG domains, a 21 aa transmembrane segment, and a 631 aa cytoplasmic domain. Plexin A1 binds the transmembrane Semaphorin 6D directly and binds the Class 3 secreted Semaphorins indirectly via Neuropilin-1 and -2. It mediates cytoskeletal remodeling that results in cell migration and axon repulsion. Within aa 964 - 1152 (in the IPT/TIG region), human Plexin A1 shares 93% aa sequence identity with mouse and rat Plexin A1.