Download MendeleyStructural basis for SMAC-mediated antagonism of caspase inhibition by the giant ubiquitin ligase BIRC6.
Dietz, L., Ellison, C.J., Riechmann, C., Cassidy, C.K., Felfoldi, F.D., Pinto-Fernandez, A., Kessler, B.M., Elliott, P.R.(2023) Science 379: 1112-1117
- PubMed: 36758106
- DOI: https://doi.org/10.1126/science.ade8840
- Primary Citation of Related Structures:
8ATM, 8ATO - PubMed Abstract:
Certain inhibitor of apoptosis (IAP) family members are sentinel proteins that prevent untimely cell death by inhibiting caspases. Antagonists, including second mitochondria-derived activator of caspases (SMAC), regulate IAPs and drive cell death. Baculoviral IAP repeat-containing protein 6 (BIRC6), a giant IAP with dual E2 and E3 ubiquitin ligase activity, regulates programmed cell death through unknown mechanisms. We show that BIRC6 directly restricts executioner caspase-3 and -7 and ubiquitinates caspase-3, -7, and -9, working exclusively with noncanonical E1, UBA6. Notably, we show that SMAC suppresses both mechanisms. Cryo-electron microscopy structures of BIRC6 alone and in complex with SMAC reveal that BIRC6 is an antiparallel dimer juxtaposing the substrate-binding module against the catalytic domain. Furthermore, we discover that SMAC multisite binding to BIRC6 results in a subnanomolar affinity interaction, enabling SMAC to competitively displace caspases, thus antagonizing BIRC6 anticaspase function.
Organizational Affiliation:
Department of Biochemistry, University of Oxford, Oxford, OX1 3QU, UK.
