Zeng Lei, Yap Kyoko L, Ivanov Alexey V, Wang Xueqi, Mujtaba Shiraz, Plotnikova Olga, Rauscher Frank J, Zhou Ming-Ming
Department of Structural and Chemical Biology, Mount Sinai School of Medicine, New York University, 1425 Madison Avenue, New York, New York 10029, USA.
Nat Struct Mol Biol. 2008 Jun;15(6):626-33. doi: 10.1038/nsmb.1416. Epub 2008 May 18.
The tandem PHD finger-bromodomain, found in many chromatin-associated proteins, has an important role in gene silencing by the human co-repressor KRAB-associated protein 1 (KAP1). Here we report the three-dimensional solution structure of the tandem PHD finger-bromodomain of KAP1. The structure reveals a distinct scaffold unifying the two protein modules, in which the first helix, alpha(Z), of an atypical bromodomain forms the central hydrophobic core that anchors the other three helices of the bromodomain on one side and the zinc binding PHD finger on the other. A comprehensive mutation-based structure-function analysis correlating transcriptional repression, ubiquitin-conjugating enzyme 9 (UBC9) binding and SUMOylation shows that the PHD finger and the bromodomain of KAP1 cooperate as one functional unit to facilitate lysine SUMOylation, which is required for KAP1 co-repressor activity in gene silencing. These results demonstrate a previously unknown unified function for the tandem PHD finger-bromodomain as an intramolecular small ubiquitin-like modifier (SUMO) E3 ligase for transcriptional silencing.
在许多与染色质相关的蛋白质中发现的串联植物同源结构域（PHD）-溴结构域，在人类共抑制因子KRAB相关蛋白1（KAP1）介导的基因沉默中发挥重要作用。在此，我们报道了KAP1串联PHD-溴结构域的三维溶液结构。该结构揭示了一种独特的支架结构，将两个蛋白质模块统一起来，其中非典型溴结构域的第一个螺旋α(Z)形成了中央疏水核心，该核心在一侧锚定溴结构域的其他三个螺旋，在另一侧锚定锌结合PHD结构域。基于全面的基于突变的结构-功能分析，将转录抑制、泛素结合酶9（UBC9）结合和小泛素样修饰（SUMO）化相关联，结果表明KAP1的PHD结构域和溴结构域作为一个功能单元协同作用，促进赖氨酸SUMO化作用，这是KAP1在基因沉默中发挥共抑制活性所必需的。这些结果证明了串联PHD-溴结构域作为一种用于转录沉默的分子内小泛素样修饰（SUMO）E3连接酶，具有此前未知的统一功能。
