Identification of Omi/HtrA2 as a mitochondrial apoptotic serine protease that disrupts inhibitor of apoptosis protein-caspase interaction.
To identify human proteins that bind to the Smac and caspase-9 binding pocket on the baculoviral inhibitor of apoptosis protein (IAP) repeat 3 (BIR3) domain of human XIAP, we used BIR3 as an affinity reagent, followed by elution with the BIR3 binding peptide AVPIA, microsequencing, and mass spectrometry. The mature serine protease Omi (also known as HtrA2) was identified as a mitochondrial direct BIR3-binding protein and a caspase activator. Like mature Smac (also known as Diablo), mature Omi contains a conserved IAP-binding motif (AVPS) at its N terminus, which is exposed after processing of its N-terminal mitochondrial targeting sequence upon import into the mitochondria. Mature Omi is released together with mature Smac from the mitochondria into the cytosol upon disruption of the outer mitochondrial membrane during apoptosis. Finally, mature Omi can induce apoptosis in human cells in a caspase-independent manner through its protease activity and in a caspase-dependent manner via its ability to disrupt caspase-IAP interaction. Our results provide clear evidence for the involvement of a mitochondrial serine protease in the apoptotic pathway, emphasizing the critical role of the mitochondria in cell death.
Hegde
Ramesh
R
Center for Apoptosis Research and the Department of Microbiology and Immunology, Kimmel Cancer Institute, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Srinivasula
Srinivasa M
SM
Zhang
ZhiJia
Z
Wassell
Richard
R
Mukattash
Rula
R
Cilenti
Lucia
L
DuBois
Garrett
G
Lazebnik
Yuri
Y
Zervos
Antonis S
AS
Fernandes-Alnemri
Teresa
T
Alnemri
Emad S
ES
D000595:Amino Acid Sequence; D017209:Apoptosis; D020169:Caspases / Q000378:metabolism*; D000074923:High-Temperature Requirement A Serine Peptidase 2; D006801:Humans; D051034:Inhibitor of Apoptosis Proteins; D019476:Insect Proteins / Q000378:metabolism*; D008928:Mitochondria / Q000201:enzymology*; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D011506:Proteins; D012697:Serine Endopeptidases / Q000502:physiology*
D051034:Inhibitor of Apoptosis Proteins; D019476:Insect Proteins; D024101:Mitochondrial Proteins; D011506:Proteins; D012697:Serine Endopeptidases; C000615914:HTRA2 protein, human; D000074923:High-Temperature Requirement A Serine Peptidase 2; D020169:Caspases