Pringa E, Martinez-Noel G, Muller U, Harbers K
Heinrich-Pette-Institut für Experimentelle Virologie und Immunologie an der Universität Hamburg, Martinistrasse 52, D-20251 Hamburg, Germany.
J Biol Chem. 2001 Jun 1;276(22):19617-23. doi: 10.1074/jbc.M100192200. Epub 2001 Mar 23.
The U-box domain has been suggested to be a modified RING finger motif where the metal-coordinating cysteines and histidines have been replaced with other amino acids. Known U-box-containing proteins have been implicated in the ubiquitin/proteasome system. In a search for proteins interacting with the ubiquitin-conjugating enzyme UbcM4/UbcH7, we have identified a novel U-box containing protein, termed UIP5, that is exclusively found in the nucleus as part of a nuclear dot-like structure. Interaction between UbcM4 and UIP5 was observed in vivo and in vitro with bacterially expressed proteins. In addition to UbcM4, several other ubiquitin-conjugating enzymes (E2s) that share the same sequence within the L1 loop bind to UIP5. Mutational analysis showed that the U-box, like the RING finger in other proteins, forms the physical basis for the interaction with E2 enzymes. Further support for the structural similarity between U-box and RING finger comes from the observation that, in both cases, the same regions within the UbcM4 molecule are required for interaction. Our results establish at the molecular level a link between the U-box and the ubiquitin conjugating system and strongly suggest that proteins containing U-box domains are functionally closely related to RING finger proteins.
U-box结构域被认为是一种经过修饰的RING指基序，其中与金属配位的半胱氨酸和组氨酸已被其他氨基酸取代。已知含U-box的蛋白质与泛素/蛋白酶体系统有关。在寻找与泛素结合酶UbcM4/UbcH7相互作用的蛋白质时，我们鉴定出一种新型的含U-box的蛋白质，称为UIP5，它仅作为核点状结构的一部分存在于细胞核中。在体内和体外均观察到细菌表达的蛋白质UbcM4与UIP5之间的相互作用。除了UbcM4之外，其他几种在L1环内具有相同序列的泛素结合酶（E2s）也与UIP5结合。突变分析表明，U-box与其他蛋白质中的RING指一样，构成了与E2酶相互作用的物理基础。U-box与RING指在结构上相似性的进一步证据来自于以下观察结果：在这两种情况下，UbcM4分子内相同的区域都是相互作用所必需的。我们的结果在分子水平上建立了U-box与泛素结合系统之间的联系，并强烈表明含U-box结构域的蛋白质在功能上与RING指蛋白密切相关。
