Signaling together apart

After being cleaved apart, two halves of a split personality receptor protein are free to wander far away from each other, say Kirill Volynski, Yuri Ushkaryov, and colleagues (Imperial College, London, UK). But when signaling is needed the two halves reunite.

The receptor, called latrophilin, is known only as a binding site for the black widow poison latrotoxin. Although no endogenous ligand for latrophilin is known, a varied family of receptors exists with a similar organization. Each family member has two domains: an NH₂-terminal fragment (NTF) that interacts with other cell surface or possibly extracellular matrix proteins, and a COOH-terminal fragment (CTF) that resembles a G-protein–coupled receptor (GPCR). The two domains were known to be cleaved, but the persistence of the NTF on the cell surface led previous workers to assume...