英国牛津大学Paul R. Elliott课题组揭示巨型泛素连接酶BIRC6介导Smac拮抗caspase抑制的结构基础
据研究人员介绍，某些细胞凋亡抑制子（IAP）家族成员是通过抑制半胱天冬酶来防止细胞过早死亡的哨兵蛋白。包括第二线粒体来源的半胱天冬酶激活剂（SMAC）在内的拮抗剂调节IAP，进而驱动细胞死亡。杆状病毒IAP重复蛋白6（BIRC6）是一种具有E2/E3双泛素连接酶活性的巨型IAP，通过未知机制调控程序性细胞死亡。
研究人员发现BIRC6直接限制caspases-3和-7，泛素化caspases-3， -7和-9只与非标准E1, UBA6起作用。重要的是，该课题组人员发现SMAC抑制了这两种机制。BIRC6单独和与SMAC复合物的冷冻电子显微镜结构显示BIRC6是一种反平行的二聚体，将底物结合模块与催化结构域并列。
此外，该研究团队发现SMAC与BIRC6的多位点结合导致亚纳摩尔亲和相互作用，使SMAC能够竞争性地取代caspases，从而拮抗BIRC6的抗caspase功能。
附：英文原文
Title: Structural basis for SMAC-mediated antagonism of caspase inhibition by the giant ubiquitin ligase BIRC6
Author: Larissa Dietz, Cara J. Ellison, Carlos Riechmann, C. Keith Cassidy, F. Daniel Felfoldi, Adán Pinto-Fernández, Benedikt M. Kessler, Paul R. Elliott
Issue&Volume: 2023-02-09
Abstract: Certain Inhibitors of apoptosis (IAP) family members are sentinel proteins preventing untimely cell death by inhibiting caspases. Antagonists including second mitochondria-derived activator of caspase (SMAC) regulate IAPs, driving cell death. Baculoviral IAP repeat-containing protein 6 (BIRC6), a giant IAP with dual E2/E3 ubiquitin ligase activity, regulates programmed cell death through unknown mechanisms. We show BIRC6 directly restricts executioner caspases-3 and -7, and ubiquitinates caspases-3, -7 and -9 working exclusively with non-canonical E1, UBA6. Importantly, we show SMAC suppresses both mechanisms. Cryo-electron microscopy structures of BIRC6 alone and in complex with SMAC reveals BIRC6 is an anti-parallel dimer juxtaposing the substrate-binding module against the catalytic domain. Furthermore, we discover SMAC multi-site binding to BIRC6 results in a sub-nanomolar affinity interaction, enabling SMAC to competitively displace caspases thus antagonizing BIRC6 anti-caspase function.
DOI: ade8840
Source: https://www.science.org/doi/10.1126/science.ade8840