Neuronal apoptosis-inhibitory protein does not interact with Smac and requires ATP to bind caspase-9.
The neuronal apoptosis-inhibitory protein (NAIP) is the founding member of the mammalian family of inhibitor of apoptosis (IAP) proteins (also known as BIRC proteins) and has been shown to be antiapoptotic both in vivo and in vitro. The 160-kDa NAIP contains three distinct regions: an amino-terminal cluster of three baculoviral inhibitory repeat (BIR) domains, a central nucleotide binding oligomerization domain (NOD), and a carboxyl-terminal leucine-rich repeat (LRR) domain. The presence of the NOD and LRR domains renders NAIP unique among the IAPs and suggests that NAIP activity is regulated in a manner distinct from that of other members of the family. In this report, we examined the interaction of various regions of NAIP with caspase-9 and Smac. Recombinant NAIPs with truncations of the carboxyl-terminal LRR or NOD-LRR regions bound to caspase-9. In contrast, the full-length protein did not, suggesting some form of structural autoregulation. However, the association of the wild type full-length protein with caspase-9 was observed when interaction analysis was performed in the presence of ATP. Furthermore, mutation of the NAIP ATP binding pocket allowed full-length protein to interact with caspase-9. Thus, we conclude that NAIP binds to caspase-9 with a structural requirement for ATP and that in the absence of ATP the LRR domain negatively regulates the caspase-9-inhibiting activity of the BIR domains. Interestingly, and in contrast to the X-chromosome-linked inhibitor of apoptosis protein (XIAP), NAIP-mediated inhibition of caspase-9 was not countered by a peptide containing an amino-terminal IAP binding motif (IBM). Consistent with this observation was the failure of Smac protein to interact with the NAIP BIR domains. These results demonstrate that NAIP is distinct from the other IAPs, both in demonstrating a ligand-dependent caspase-9 interaction and in demonstrating a distinct mechanism of inhibition.
Solange Gauthier Karsh Laboratory, Children's Hospital of Eastern Ontario Research Institute, Ottawa, Ontario K1H 8L1, Canada. jamshid@mgcheo.med.uottawa.ca
Jamshid
J
Davoodi
Lily
L
Lin
John
J
Kelly
Peter
P
Liston
Alexander E
AE
MacKenzie
D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism*; D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D017209:Apoptosis; D051017:Apoptosis Regulatory Proteins; D015153:Blotting, Western; D002352:Carrier Proteins / Q000737:chemistry; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism*; D002845:Chromatography; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004926:Escherichia coli / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D007930:Leucine / Q000737:chemistry; D008024:Ligands; D024101:Mitochondrial Proteins / Q000737:chemistry; D008957:Models, Genetic; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D009419:Nerve Tissue Proteins / Q000502:physiology*; D051616:Neuronal Apoptosis-Inhibitory Protein; D009474:Neurons / Q000378:metabolism*; D010957:Plasmids / Q000378:metabolism; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011506:Proteins / Q000737:chemistry; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D013997:Time Factors; D014162:Transfection; D051636:X-Linked Inhibitor of Apoptosis Protein
D051017:Apoptosis Regulatory Proteins; D002352:Carrier Proteins; C412403:DIABLO protein, human; D018076:DNA, Complementary; D047908:Intracellular Signaling Peptides and Proteins; D008024:Ligands; D024101:Mitochondrial Proteins; C496800:NAIP protein, human; D009419:Nerve Tissue Proteins; D051616:Neuronal Apoptosis-Inhibitory Protein; D011506:Proteins; D011994:Recombinant Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D000255:Adenosine Triphosphate; C506433:CASP9 protein, human; D053453:Caspase 9; D020169:Caspases; D007930:Leucine