Ubiquitin-like Protein Transfer Cascades

描述（由申请人提供）：泛素样蛋白（UBLs）如ubiquitin (Ub)， NEDD8和SUMO的共价附着是真核蛋白调控的主要形式。ubl修饰大量的蛋白质，以各种方式改变它们的功能。UBL修饰可以影响靶标的半衰期、亚细胞定位、酶活性或与蛋白质或DNA伴侣相互作用的能力。因此，UBLs调节了许多生物过程，如细胞周期、信号转导、细胞凋亡、免疫反应、自噬和发育。UBL通路的缺陷与疾病广泛相关，包括癌症、发育障碍、高血压、神经退行性疾病和恶病质。我们建议将我们在UBL结合方面的专业知识扩展到两个最大的E3家族：RING（非常有趣的新基因-预计在人类中为570）和HECT（与E6AP C-Terminus同源-预计在人类中为28）。在RING E3s中，最大的一类由模块化的多亚基Cullin-RING （CRL）家族组成。CRLs依次与不同的E2s起作用，修饰不同的靶标：首先RING结构域结合NEDD8 E2，然后通过NEDD8的自修饰激活cullin亚基。然后CRL绑定加载了Ub的E2，它是要传输到目标的Ub的源。HECT E3s利用一种独特的机制，其中HECT结构域催化Cys通过硫酯连接的中间体直接参与。首先，HECT结构域结合硫酯连接的E2~Ub配合物，并将Ub从E2 Cys转移到HECT结构域的催化Cys上。最终，Ub从HECT E3细胞转移到一个或多个Ub细胞。我们提出了一个以结构生物学和生物化学为重点的研究计划，以了解CRL E3s（目标1）和HECT E3s（目标2）的功能机制。

DESCRIPTION (provided by applicant): Covalent attachment of ubiquitin-like proteins (UBLs) such as ubiquitin (Ub), NEDD8, and SUMO is a predominant form of eukaryotic protein regulation. UBLs modify a vast number of proteins, altering their functions in a variety of ways. UBL modifications can affect the target's half-life, subcellular localization, enzymatic activity, or ability to interact with protein or DNA partners. As a result, UBLs regulate numerous biological processes, such as the cell cycle, signal transduction, apoptosis, the immune response, autophagy, and development. Defects in UBL pathways are widely associated with diseases, including cancers, developmental disorders, high blood pressure, neurodegenerative disorders, and cachexia. We propose to extend our expertise on UBL conjugation to the two largest E3 families: RING (Really Interesting New Gene - 570 predicted in humans) and HECT (Homologous to E6AP C-Terminus - 28 predicted in humans). Among the RING E3s, the largest class consists of the modular, multisubunit Cullin-RING (CRL) family. CRLs function sequentially with distinct E2s to modify distinct targets: first the RING domain binds a NEDD8 E2, and the cullin subunit is activated by self-modification with NEDD8. Then a CRL binds a Ub-loaded E2, which is the source of Ub to be transferred to a target. HECT E3s utilize a distinct mechanism, in which a HECT domain catalytic Cys participates directly via a thioester-linked intermediate. First, the HECT domain binds a thioester-linked E2~Ub complex, and Ub is transferred from the E2 Cys to the HECT domain catalytic Cys. Ultimately Ub is transferred from the HECT E3 Cys to a target or Ub Lys. We propose a research plan focused on structural biology and biochemistry to understand mechanisms underlying functions of CRL E3s (Aim 1) and HECT E3s (Aim 2). PUBLIC HEALTH RELEVANCE: Ubiquitin-like protein (UBL) conjugation regulates many biological processes, including cell division, the immune response, development and signal transduction, and defects in UBL pathways have been widely associated with cancers, neurodegenerative disorders, developmental disorders, heart diseases (e.g., high blood pressure), and viral and retroviral infections. The recent approval of the proteasome inhibitor Bortezomib (VelcadeTM) for treatment of multiple myeloma underscores the therapeutic potential for targeting enzymes in the ubiquitin, and UBL, pathways, and highlights the importance of understanding the detailed mechanisms and specificities of these enzymes. Thus, we anticipate that knowledge of the mechanisms by which enzymes transfer UBLs as revealed by the proposed studies will be of broad significance to many human diseases, much like studies of protein kinases have influenced our knowledge of signaling pathways and their roles in diseases.