title: X-linked inhibitor of apoptosis protein (XIAP) inhibits caspase-3 and -7 in distinct modes.
abstract: The inhibitor of apoptosis proteins (IAP) regulates cell death by inhibiting caspases. The region of X-linked (X) IAP containing the second baculovirus IAP repeat domain (BIR2) is sufficient for inhibiting caspase-3 and -7. In this study, we found that the modes of inhibition of these two caspases were different: caspase-3 is inhibited in a competitive manner whereas caspase-7 inhibition occurs through a mixed competitive and noncompetitive mechanism. Binding assays revealed that the inhibition of caspase-3 by XIAP was totally dependent on the interaction between the active site of caspase-3 and the linker region between the BIR1 and BIR2 domains of XIAP. In contrast, the active site and the NH(2)-terminal region of caspase-7 bound to the linker region and the BIR2, respectively. Moreover the BIR2 with a mutated linker region, which inhibited caspase-3 very weakly, still bound to and inhibited caspase-7. Furthermore, a chimeric caspase-7/3 comprising the NH(2)-terminal portion of caspase-7 and COOH-terminal portion of caspase-3 was inhibited by XIAP by a mixed competitive and noncompetitive mechanism. Our results suggest that the linker region between BIR1 and BIR2 domains is responsible for active site-directed, competitive inhibition of both caspase-3 and -7, whereas the BIR2 itself is involved in noncompetitive inhibition of caspase-7.
authors.affiliation: Laboratory for Motor System Neurodegeneration, RIKEN-Brain Science Institute, Wako City, Saitama 351-0198, Japan.
authors.forename: Y
authors.initials: Y
authors.lastname: Suzuki
authors.forename: Y
authors.initials: Y
authors.lastname: Nakabayashi
authors.forename: K
authors.initials: K
authors.lastname: Nakata
authors.forename: J C
authors.initials: JC
authors.lastname: Reed
authors.forename: R
authors.initials: R
authors.lastname: Takahashi
mesh_terms: D001483:Base Sequence; D001665:Binding Sites; D053148:Caspase 3; D053179:Caspase 7; D061945:Caspase Inhibitors; D017931:DNA Primers; D008040:Genetic Linkage; D011506:Proteins / Q000502:physiology*; D014960:X Chromosome; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D061945:Caspase Inhibitors; D017931:DNA Primers; D011506:Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; D053148:Caspase 3; D053179:Caspase 7