title: Direct inhibition of caspase 3 is dispensable for the anti-apoptotic activity of XIAP.
abstract: XIAP is a mammalian inhibitor of apoptosis protein (IAP). To determine residues within the second baculoviral IAP repeat (BIR2) required for inhibition of caspase 3, we screened a library of BIR2 mutants for loss of the ability to inhibit caspase 3 toxicity in the yeast Schizosaccharomyces pombe. Four of the mutations, not predicted to affect the structure of the BIR fold, clustered together on the N-terminal region that flanks BIR2, suggesting that this is a site of interaction with caspase 3. Introduction of these mutations into full-length XIAP reduced caspase 3 inhibitory activity up to 500-fold, but did not affect its ability to inhibit caspase 9 or interact with the IAP antagonist DIABLO. Furthermore, these mutants retained full ability to inhibit apoptosis in transfected cells, demonstrating that although XIAP is able to inhibit caspase 3, this activity is dispensable for inhibition of apoptosis by XIAP in vivo.
authors.affiliation: The Walter and Eliza Hall Institute of Medical Research, Post Office Royal Melbourne Hospital, VIC 3050. silke@wehi.edu.au
authors.forename: J
authors.initials: J
authors.lastname: Silke
authors.forename: P G
authors.initials: PG
authors.lastname: Ekert
authors.forename: C L
authors.initials: CL
authors.lastname: Day
authors.forename: C J
authors.initials: CJ
authors.lastname: Hawkins
authors.forename: M
authors.initials: M
authors.lastname: Baca
authors.forename: J
authors.initials: J
authors.lastname: Chew
authors.forename: M
authors.initials: M
authors.lastname: Pakusch
authors.forename: A M
authors.initials: AM
authors.lastname: Verhagen
authors.forename: D L
authors.initials: DL
authors.lastname: Vaux
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D017209:Apoptosis; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D053453:Caspase 9; D061945:Caspase Inhibitors; D020169:Caspases / Q000235:genetics / Q000378:metabolism; D004789:Enzyme Activation; D015870:Gene Expression; D051034:Inhibitor of Apoptosis Proteins; D024101:Mitochondrial Proteins; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011506:Proteins / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D012568:Schizosaccharomyces; D014466:Ultraviolet Rays; D014764:Viral Proteins / Q000235:genetics; D051636:X-Linked Inhibitor of Apoptosis Protein
chemical_list: D002352:Carrier Proteins; D061945:Caspase Inhibitors; D051034:Inhibitor of Apoptosis Proteins; D024101:Mitochondrial Proteins; D011506:Proteins; D014764:Viral Proteins; D051636:X-Linked Inhibitor of Apoptosis Protein; C086430:inhibitor of apoptosis, Nucleopolyhedrovirus; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases