Rao-Naik C, delaCruz W, Laplaza J M, Tan S, Callis J, Fisher A J
Section of Molecular and Cellular Biology, University of California, Davis, California 95616, USA.
J Biol Chem. 1998 Dec 25;273(52):34976-82. doi: 10.1074/jbc.273.52.34976.
Several proteins with significant identity to ubiquitin have been characterized recently. In contrast to ubiquitin's main role in targeting proteins for degradation, a described function of one family of ubiquitin-related proteins, the Rub family, is to serve as a stable post-translational modification of a complex involved in the G1-to-S cell cycle transition. Rub proteins have been found in animals, plants, and fungi and consist of 76 residues with 52-63% identity to ubiquitin. In this study three different RUB proteins within the plant Arabidopsis are identified; two differ by only 1 amino acid, while the third is only 77.6% identical to the other two. Genes encoding all three are expressed in multiple organs. In addition, we report the crystal structure of higher plant RUB1 at 1.7-A resolution to help elucidate the functional differences between Rub and ubiquitin. RUB1 contains a single globular domain with a flexible COOH-terminal extension. The overall RUB1 structure is very similar to ubiquitin. The majority of the amino acid differences between RUB1 and ubiquitin map to the surface. These changes alter the electrostatic surface potential in two regions and likely confer specificity between ubiquitin and RUB1 and their ubiquitin-activating enzyme (E1) or E1-like activating enzymes.
最近已经鉴定出了几种与泛素具有显著同源性的蛋白质。与泛素在靶向蛋白质进行降解中的主要作用不同，泛素相关蛋白的一个家族（Rub家族）的一种已知功能是作为参与G1期到S期细胞周期转换的复合物的稳定翻译后修饰。Rub蛋白已在动物、植物和真菌中发现，由76个残基组成，与泛素的同源性为52%-63%。在本研究中，鉴定出了拟南芥中的三种不同的RUB蛋白；其中两种仅相差1个氨基酸，而第三种与其他两种的同源性仅为77.6%。编码这三种蛋白的基因在多个器官中均有表达。此外，我们报告了高等植物RUB1在1.7埃分辨率下的晶体结构，以帮助阐明Rub和泛素之间的功能差异。RUB1包含一个带有柔性COOH末端延伸的单个球状结构域。RUB1的整体结构与泛素非常相似。RUB1和泛素之间的大多数氨基酸差异位于表面。这些变化改变了两个区域的静电表面电位，并可能赋予泛素和RUB1及其泛素激活酶（E1）或E1样激活酶之间的特异性。
