title: IAP-antagonists exhibit non-redundant modes of action through differential DIAP1 binding.
abstract: The Drosophila inhibitor of apoptosis protein DIAP1 ensures cell viability by directly inhibiting caspases. In cells destined to die this IAP-mediated inhibition of caspases is overcome by IAP-antagonists. Genetic evidence indicates that IAP-antagonists are non-equivalent and function synergistically to promote apoptosis. Here we provide biochemical evidence for the non-equivalent mode of action of Reaper, Grim, Hid and Jafrac2. We find that these IAP-antagonists display differential and selective binding to specific DIAP1 BIR domains. Consistently, we show that each DIAP1 BIR region associates with distinct caspases. The differential DIAP1 BIR interaction seen both between initiator and effector caspases and within IAP-antagonist family members suggests that different IAP-antagonists inhibit distinct caspases from interacting with DIAP1. Surprisingly, we also find that the caspase-binding residues of XIAP predicted to be strictly conserved in caspase-binding IAPs, are absent in DIAP1. In contrast to XIAP, residues C-terminal to the DIAP1 BIR1 domain are indispensable for caspase association. Our studies on DIAP1 and caspases expose significant differences between DIAP1 and XIAP suggesting that DIAP1 and XIAP inhibit caspases in different ways.
authors.affiliation: The Breakthrough Toby Robins Breast Cancer Research Centre, Institute of Cancer Research, Mary-Jean Mitchell Green Building, Chester Beatty Laboratories, Fulham Road, London SW3 6JB, UK.
authors.forename: Anna
authors.initials: A
authors.lastname: Zachariou
authors.forename: Tencho
authors.initials: T
authors.lastname: Tenev
authors.forename: Lakshmi
authors.initials: L
authors.lastname: Goyal
authors.forename: Julie
authors.initials: J
authors.lastname: Agapite
authors.forename: Hermann
authors.initials: H
authors.lastname: Steller
authors.forename: Pascal
authors.initials: P
authors.lastname: Meier
mesh_terms: D000818:Animals; D017209:Apoptosis; D001665:Binding Sites; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival; D029721:Drosophila Proteins / Q000037:antagonists & inhibitors / Q000737:chemistry / Q000378:metabolism*; D004331:Drosophila melanogaster; D051034:Inhibitor of Apoptosis Proteins; D011485:Protein Binding; D016335:Zinc Fingers
chemical_list: C111891:DIAP1 protein, Drosophila; D029721:Drosophila Proteins; D051034:Inhibitor of Apoptosis Proteins; D020169:Caspases