Structural basis of caspase inhibition by XIAP: differential roles of the linker versus the BIR domain.
The inhibitor of apoptosis proteins (IAPs) represent the only endogenous caspase inhibitors and are characterized by the presence of baculoviral IAP repeats (BIRs). Here, we report the crystal structure of the complex between human caspase-7 and XIAP (BIR2 and the proceeding linker). The structure surprisingly reveals that the linker is the only contacting element for the caspase, while the BIR2 domain is invisible in the crystal. The linker interacts with and blocks the substrate groove of the caspase in a backward fashion, distinct from substrate recognition. Structural analyses suggest that the linker is the energetic and specificity determinant of the interaction. Further biochemical characterizations clearly establish that the linker harbors the major energetic determinant, while the BIR2 domain serves as a regulatory element for caspase binding and Smac neutralization.
Huang
Y
Y
Program in Physiology, Biophysics and Molecular Medicine, Graduate School of Medical Sciences, of Cornell University, 1300 York Avenue, New York, NY 10021, USA.
Park
Y C
YC
Rich
R L
RL
Segal
D
D
Myszka
D G
DG
Wu
H
H
D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; D053179:Caspase 7; D020169:Caspases / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D020134:Catalytic Domain; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D017433:Protein Structure, Secondary; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013379:Substrate Specificity; D051636:X-Linked Inhibitor of Apoptosis Protein
D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; C412403:DIABLO protein, human; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D011506:Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; C505520:CASP7 protein, human; D053179:Caspase 7; D020169:Caspases