Poly(ADP-ribose) glycohydrolase (PARG) regulates cellular poly(ADP-ribose) (PAR) levels by rapidly cleaving glycosidic bonds between ADP-ribose units. PARG interacts with proliferating cell nuclear antigen (PCNA) and is strongly recruited to DNA damage sites in a PAR- and PCNA-dependent fashion. Here we identified PARG acetylation site K409 that is essential for its interaction with PCNA, its localization within replication foci and its recruitment to DNA damage sites. We found K409 to be part of a non-canonical PIP-box within the PARG disordered regulatory region. The previously identified putative N-terminal PIP-box does not bind PCNA directly but contributes to PARG localization within replication foci. X-ray structure and MD simulations reveal that the PARG non-canonical PIP-box binds PCNA in a manner similar to other canonical PIP-boxes and may represent a new type of PIP-box. While the binding of previously described PIP-boxes is based on hydrophobic interactions, PARG PIP-box binds PCNA via both stabilizing hydrophobic and fine-tuning electrostatic interactions. Our data explain the mechanism of PARG–PCNA interaction through a new PARG PIP-box that exhibits non-canonical sequence properties but a canonical mode of PCNA binding.

中文翻译：

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一种新颖的非经典PIP盒介导PARG与PCNA的相互作用

聚（ADP-核糖）糖水解酶（PARG）通过快速切割ADP-核糖单元之间的糖苷键来调节细胞的聚（ADP-核糖）（PAR）水平。PARG与增殖细胞核抗原（PCNA）相互作用，并以PAR和PCNA依赖性方式强烈募集到DNA损伤位点。在这里，我们确定了PARG乙酰化位点K409，这对于其与PCNA的相互作用，其在复制灶内的定位以及其对DNA损伤位点的募集都是必不可少的。我们发现K409是PARG无序调节区域内非经典PIP盒的一部分。先前确定的推定的N末端PIP盒不直接结合PCNA，但有助于复制灶内的PARG定位。X射线结构和MD模拟显示，PARG非规范PIP盒以类似于其他规范PIP盒的方式绑定PCNA，可能代表了一种新型的PIP盒。尽管先前描述的PIP盒的结合是基于疏水相互作用，但PARG PIP盒通过稳定疏水和微调静电相互作用来结合PCNA。我们的数据通过一个新的PARG PIP盒解释了PARG-PCNA相互作用的机制，该盒具有非规范的序列特性，但具有PCNA结合的规范模式。