Neuropilin

Neuropilin is a protein receptor active in neurons.

Overview
There are two forms of Neuropilins, NRP-1 and NRP-2. They are transmembrane glycoproteins, and predominantly co-receptors for another class of proteins known as Semaphorins. Of the Semaphorins, NRP-1 and NRP-2 are specically receptors for Class-3 Semaphorins, which, amongst many things, are responsible for axon guidance during the development of the nervous system in vertebrates.

Neuropilins work as co-receptors as they have a very small cytoplasmic domain and thus rely upon other molecules to transduce their signals across a cell membrane, normally Plexins. Neuropilins generally work as dimers and different combinations have different affinities for molecules. For example, NRP-1 homodimers have high affinity for Sema-3A, whilst NRP-2 homodimers have high affinity for Sema-3F.

Another ligand for neuropilins is VEGF, a growth hormone involved in the regulation of angiogenesis.