A conserved XIAP-interaction motif in caspase-9 and Smac/DIABLO regulates caspase activity and apoptosis

Srinivasa M. Srinivasula, Ramesh Hegde, Ayman Saleh, Pinaki Datta, Eric Shiozaki, Jijie Chai, Ryung-Ah Lee, Paul D. Robbins, Teresa Fernandes-Alnemri, Yigong Shi and Emad S. Alnemri ()
Additional contact information
Srinivasa M. Srinivasula: Kimmel Cancer Institute, Thomas Jefferson University
Ramesh Hegde: Kimmel Cancer Institute, Thomas Jefferson University
Ayman Saleh: University of Pittsburgh
Pinaki Datta: Kimmel Cancer Institute, Thomas Jefferson University
Eric Shiozaki: Lewis Thomas Laboratory, Princeton University
Jijie Chai: Lewis Thomas Laboratory, Princeton University
Ryung-Ah Lee: Kimmel Cancer Institute, Thomas Jefferson University
Paul D. Robbins: University of Pittsburgh
Teresa Fernandes-Alnemri: Kimmel Cancer Institute, Thomas Jefferson University
Yigong Shi: Lewis Thomas Laboratory, Princeton University
Emad S. Alnemri: Kimmel Cancer Institute, Thomas Jefferson University

Nature, 2001, vol. 410, issue 6824, 112-116

Abstract: Abstract X-linked inhibitor-of-apoptosis protein (XIAP) interacts with caspase-9 and inhibits its activity1,2,3, whereas Smac (also known as DIABLO) relieves this inhibition through interaction with XIAP4,5,6,7. Here we show that XIAP associates with the active caspase-9–Apaf-1 holoenzyme complex through binding to the amino terminus of the linker peptide on the small subunit of caspase-9, which becomes exposed after proteolytic processing of procaspase-9 at Asp 315. Supporting this observation, point mutations that abrogate the proteolytic processing but not the catalytic activity of caspase-9, or deletion of the linker peptide, prevented caspase-9 association with XIAP and its concomitant inhibition. We note that the N-terminal four residues of caspase-9 linker peptide share significant homology with the N-terminal tetra-peptide in mature Smac and in the Drosophila proteins Hid/Grim/Reaper8,9, defining a conserved class of IAP-binding motifs. Consistent with this finding, binding of the caspase-9 linker peptide and Smac to the BIR3 domain of XIAP is mutually exclusive, suggesting that Smac potentiates caspase-9 activity by disrupting the interaction of the linker peptide of caspase-9 with BIR3. Our studies reveal a mechanism in which binding to the BIR3 domain by two conserved peptides, one from Smac and the other one from caspase-9, has opposing effects on caspase activity and apoptosis.

Date: 2001
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DOI: 10.1038/35065125

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