Cysteine 230 is essential for the structure and activity of the cytotoxic ligand TRAIL

Unlike other tumor necrosis factor family members, the cytotoxic ligand tum or necrosis factor-related apoptosis-inducing ligand (TRAIL)/Apo-2L contain s an unpaired cysteine residue (Cys(230)) in its receptor-binding domain. H ere we show that the biological activity of both soluble recombinant TRAIL and cell-associated, full-length TRAIL is critically dependent on the prese nce of Cys(230). Mutation of Cys(230) to alanine or serine strongly affecte d its ability to kill target cells. Binding to its receptors was decreased by at least 200-fold, and the stability of its trimeric structure was reduc ed. In recombinant TRAIL, Cys(230) was found engaged either in interchain d isulfide bridge formation, resulting in poorly active TRAIL, or in the chel ation of one zinc atom per TRAIL trimer in the active, pro-apoptotic form o f TRAIL.