The linker region preceding BIR2 of XIAP is responsible for the inhibition of caspase-3 and -7, which is further stabilized by interaction with the BIR2 domain itself (Scott et al. 2005). Binding of a dimeric SMAC (DIABLO) N-terminal peptide with the BIR2 domain of XIAP effectively antagonized inhibition of caspase-7 by XIAP (Wu G et al. 2000; Chai J et al. 2000). As DIABLO has a higher affinity for the BIR2 domain than caspase-7, DIABLO (SMAC) binding to XIAP results in the liberation of caspase-7 (Huang et al. 2001).