Structure of the UNC5H2 death domain

UNC5Hs ( UNC5H1-4) are netrin 1 receptors that are involved in axonal guidance and neuronal migration. They are dependence receptors that mediate apoptosis in the absence of netrin 1. UNC5H2-induced apoptosis depends on the interaction of the death domain at the C-terminus with the DAP-kinase death domain and caspase cleavage near the transmembrane region. Here, the crystal structure of the mouse UNC5H2 death domain has been determined at 2.1 angstrom resolution. The domain adopts a six-helix bundle fold, which is similar to those of the other members of the death-domain superfamily. The UNC5H2 death domain is a dimer in the crystal and in solution. This homodimerized structure may represent the structure of the death domain when netrin 1 binds to the UNC5H2 receptor. Homodimerization of UNC5H2 may block the access of caspase to the cleavage site. In the death-domain dimer, residues in alpha 3 and the 3(10)-helix preceding alpha 3 and the residues in alpha 4 make significant contacts, mainly by hydrophobic and van der Waals interactions.