Baba Daichi, Maita Nobuo, Jee Jun-Goo, Uchimura Yasuhiro, Saitoh Hisato, Sugasawa Kaoru, Hanaoka Fumio, Tochio Hidehito, Hiroaki Hidekazu, Shirakawa Masahiro
Graduate School of Integrated Science, Yokohama City University, Yokohama 230-0045, Japan.
Nature. 2005 Jun 16;435(7044):979-82. doi: 10.1038/nature03634.
Members of the small ubiquitin-like modifier (SUMO) family can be covalently attached to the lysine residue of a target protein through an enzymatic pathway similar to that used in ubiquitin conjugation, and are involved in various cellular events that do not rely on degradative signalling via the proteasome or lysosome. However, little is known about the molecular mechanisms of SUMO-modification-induced protein functional transfer. During DNA mismatch repair, SUMO conjugation of the uracil/thymine DNA glycosylase TDG promotes the release of TDG from the abasic (AP) site created after base excision, and coordinates its transfer to AP endonuclease 1, which catalyses the next step in the repair pathway. Here we report the crystal structure of the central region of human TDG conjugated to SUMO-1 at 2.1 A resolution. The structure reveals a helix protruding from the protein surface, which presumably interferes with the product DNA and thus promotes the dissociation of TDG from the DNA molecule. This helix is formed by covalent and non-covalent contacts between TDG and SUMO-1. The non-covalent contacts are also essential for release from the product DNA, as verified by mutagenesis.
小泛素样修饰物（SUMO）家族的成员可以通过一种类似于泛素缀合过程中使用的酶促途径，共价连接到靶蛋白的赖氨酸残基上，并参与各种不依赖蛋白酶体或溶酶体降解信号的细胞事件。然而，关于SUMO修饰诱导的蛋白质功能转移的分子机制，人们了解甚少。在DNA错配修复过程中，尿嘧啶/胸腺嘧啶DNA糖基化酶TDG的SUMO缀合促进了TDG从碱基切除后产生的无碱基（AP）位点的释放，并协调其转移至AP核酸内切酶1，后者催化修复途径的下一步。在此，我们报告了与SUMO-1缀合的人TDG中心区域在2.1埃分辨率下的晶体结构。该结构揭示了一个从蛋白质表面突出的螺旋，它可能会干扰产物DNA，从而促进TDG从DNA分子上解离。这个螺旋是由TDG和SUMO-1之间的共价和非共价接触形成的。通过诱变验证，非共价接触对于从产物DNA释放也是必不可少的。
