The recruitment of 53BP1 to chromatin, mediated by its recognition of histone H4 dimethylated at lysine 20 (H4K20me2), is important for DNA double-strand break repair. Using a series of small molecule antagonists, we demonstrate a conformational equilibrium between an open and a pre-existing lowly populated closed state of 53BP1 in which the H4K20me2 binding surface is buried at the interface between two interacting 53BP1 molecules. In cells, these antagonists inhibit the chromatin recruitment of wild type 53BP1, but do not affect 53BP1 variants unable to access the closed conformation despite preservation of the H4K20me2 binding site. Thus, this inhibition operates by shifting the conformational equilibrium toward the closed state. Our work therefore identifies an auto-associated form of 53BP1—autoinhibited for chromatin binding—that can be stabilized by small molecule ligands encapsulated between two 53BP1 protomers. Such ligands are valuable research tools to study the function of 53BP1 and have the potential to facilitate the development of new drugs for cancer therapy.

53BP1 通过识别 20 位赖氨酸二甲基化的组蛋白 H4 (H4K20me2) 介导向染色质的募集，对于 DNA 双链断裂修复非常重要。使用一系列小分子拮抗剂，我们证明了 53BP1 的开放状态和预先存在的低密度闭合状态之间的构象平衡，其中 H4K20me2 结合表面埋在两个相互作用的 53BP1 分子之间的界面处。在细胞中，这些拮抗剂抑制野生型 53BP1 的染色质募集，但不影响尽管保留了 H4K20me2 结合位点但无法进入闭合构象的 53BP1 变体。因此，这种抑制作用是通过将构象平衡移向闭合状态来实现的。因此，我们的工作确定了 53BP1 的自动关联形式（染色质结合自动抑制），可以通过封装在两个 53BP1 原聚体之间的小分子配体来稳定。此类配体是研究 53BP1 功能的有价值的研究工具，并有可能促进癌症治疗新药的开发。