STRUCTURE/FUNCTION OF UBIQUITIN CONJUGATING ENZYMES

泛素与蛋白质的翻译后结合被用于 以真核生物为靶点的多种蛋白质进行选择性降解。 许多细胞需要选择性地去除蛋白质 进程和对泛素的要求已显示为进程 从决定细胞在分裂、分化中的命运， 肿瘤的发生和衰老到更具体的过程，如DNA修复， 炎症反应、信号转导与异常清除 蛋白质。其中许多过程也在接受严密的调查 因为它们与人类疾病有关。肿瘤的发生和发展 炎症反应就是两个例子。 蛋白质泛素化的特异性是由一个家族赋予的 相关蛋白质称为泛素结合酶(UBC)。中的成员 该家族与一组不同的底物结合蛋白相互作用。 (也称为E3)，正是UBC和E3之间的这些级联交互作用 E3蛋白，使该途径能够靶向广泛的蛋白质 退化。 UBC蛋白都有大约150-170个共同的保守结构域 氨基酸残基。I类酶是最小的，是 完全由这个领域组成。这个保守的领域在更大的， 多功能UBC也可以自主发挥作用。因此，必须有 嵌入在一个保守的区域中的独特结构特征 使每种酶能够特异性相互作用的单个UBC蛋白 有自己的一套E3蛋白质。UBC序列分析及三种 已知的第I类酶的晶体结构使我们制定了一种 预测UBC的相似性和差异性的通用模型 在结构上表现出来。我们的长期目标是确定具体到什么程度 UBC蛋白中的区域被用于其功能。具体目标 对于这一研究时期是1)分析突变对 酵母中部分UBC的功能，目的是 定义负责与E3的UBC交互的那些区域， 2)开始研究确定UBC4-E3的晶体结构 复合体；3)定义在Ubc7依赖中起作用的E3蛋白 路径。

The posttranslational attachment of ubiquitin to proteins is used in eukaryotes to target a broad range of proteins for selective degradation. Selective removal of proteins is required for a number of cellular processes and a requirement for ubiquitin has been shown for processes ranging from the determination of cell fate in division, differentiation, oncogenesis and senescence to more specific processes such as DNA repair, inflammatory response, signal transduction and the removal of abnormal proteins. Many of these processes are also under intense investigation because of their relevance in human diseases. Oncogenesis and the inflammatory responses are two examples. The specificity of protein ubiquitination is conferred by a family of related proteins known as ubiquitin conjugating-enzymes (Ubc). Members in this family interact with a distinct set of substrate-binding proteins (also known as E3), and it is these cascades of interaction between Ubc and E3 proteins that enable the pathway to target a broad range of proteins for degradation. Ubc proteins all share a common conserved domain of approximately 150-170 amino acid residues. The Class I enzymes are the smallest and are comprised entirely of this domain. This conserved domain in larger, multifunctional Ubc's can also function autonomously. Thus, there must be unique structural features embedded in the conserved domain of an individual Ubc protein that enable each enzyme to interact specifically with its own set of E3 proteins. Analyses of Ubc sequences and the three known crystal structures of Class I enzymes have led us to formulate a general model that predicts how similarity and differences in Ubc's are manifested structurally. Our long term goal is to determine how specific regions in Ubc proteins are utilized for its function. The specific aims for this research period is 1) to analyze the effect of mutations on the function of selected Ubc's in the yeast S. cerevisiae, with the intention of defining those regions that are responsible for Ubc interaction with E3, 2)to initiate studies toward determining the crystal structure of a Ubc4-E3 complex; 3) to define E3 proteins that function in the Ubc7-dependent pathway.