Plexin B1 is a 300kD member of the B subfamily, plexin family of semaphorin receptors. Mature human Plexin B1 is a 2116aa type I transmembrane (TM) glycoprotein that contains a 1471aa extracellular domain (ECD) and a 612aa cytoplasmic region. The ECD contains one semaphorin domain, two PSI domains, and three IPT repeats. The ECD is cleaved into two subunits, a 200kD A-chain (aa20-1305) and a 100kD TM B-chain. The subunits are nondisulfide-linked and generate a high-affinity receptor. Plexin B1 is a receptor for CD100/Sema4D. It forms a receptor complex with neuropilins, MET, and EGFR2. Multiple splice variants are known. One shows a deletion of aa689-871. A second shows a 53aa substitution for aa677-2135. And a third shows a 53aa substitution for the 53aa between aa677-729. Over aa35-150, human Plexin B1 is 90% and 97% aa identical to dog and mouse Plexin B1, respectively.