Neuropilin-1 (Npn-1, previously known as neuropilin) and Neuropilin-2 (previously known as Npn-1-related molecule) are type I transmembrane proteins that bind distinct members of the class III secreted semaphorin subfamily that are implicated in repulsive axon guidance. Neuropilin extracellular domains contain two CUB (complement-binding) domains, two domains with homology to coagulation factors V and VIII, and a MAM (meprin) domain. In the absence of ligands, neuropilins can form homo- and hetero-oligomers via their MAM domains. Expression in developing neurons of the central and peripheral nervous systems is somewhat overlapping but distinct. Npn-1 and Npn-2 are also receptors for VEGF165 on endothelial and tumor cells.