The E3 ubiquitin ligase adaptor cereblon targets the C-terminal cyclic imide degron

The E3 ligase factor cereblon (CRBN) is a target of thalidomide and lenalidomide, which are therapeutic agents used in the treatment of hematopoietic malignancies and as ligands for targeted protein degradation. These agents are proposed to mimic a naturally occurring degron; however, the structural motif recognized by the thalidomide-binding domain of CRBN is unknown. Here, we report that C-terminal cyclic imides, post-translational modifications that arise from intramolecular cyclization of glutamine or asparagine residues, are degrons for CRBN. Dipeptides bearing the cyclic imide degron are substitutes for thalidomide when embedded within bifunctional small molecule degraders. Installation of the degron to the C-terminus of proteins induces CRBN-dependent ubiquitylation and degradation in vitro and in cells. C-Terminal cyclic imides are previously underappreciated post-translational modifications found throughout the human proteome that are endogenously recognized and removed by CRBN. The discovery of the cyclic imide degron defines a novel regulatory process controlled by these modifications, which may impact the development of therapeutic agents that engage CRBN.

E3泛素连接酶因子cereblon（CRBN）是沙利度胺（thalidomide）与来那度胺（lenalidomide）的作用靶点；这两种药物既是治疗造血系统恶性肿瘤的临床治疗剂，也可作为靶向蛋白质降解技术的配体。现有研究推测此类药物可模拟天然存在的降解基序（degron），但CRBN的沙利度胺结合结构域所识别的结构基序至今仍未明确。本研究发现，C端环酰亚胺（C-terminal cyclic imides）——一种由谷氨酰胺（glutamine）或天冬酰胺（asparagine）残基经分子内环化形成的翻译后修饰——可作为CRBN的降解基序。将携带环酰亚胺降解基序的二肽嵌入双功能小分子降解剂中时，其可替代沙利度胺发挥作用。将该降解基序引入蛋白质C端后，可在体外及细胞内诱导CRBN依赖的泛素化与蛋白质降解过程。C端环酰亚胺是一类此前未受重视的翻译后修饰，广泛存在于人类蛋白质组（human proteome）中，且可被CRBN内源识别并清除。环酰亚胺降解基序的发现，确立了一类由此类修饰调控的全新生物学过程，该发现或将影响靶向CRBN的治疗药物开发。