Figure 1.

Structure of neuropilin-1 and neuropilin-2. These proteins contain five extracellular domains, a single-pass TMD domain, and a short cytosolic tail that lacks tyrosine kinase activity. SEMA3s bind to the a1/a2/b1 segment, and Vascular endothelial growth factors (VEGFs) bind to b1/b2. The binding sites of other growth factors are not well characterized, but HGF, B-FGF, TGF-β1 were recently reported to bind both NRPs. The c domain contributes to receptor dimerization with the transmembrane domain.