Song Ai-Xin, Yang Hui, Gao Yong-Guang, Zhou Chen-Jie, Zhang Yu-Hang, Hu Hong-Yu
State Key Laboratory of Molecular Biology, Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai, China.
PLoS One. 2014 Sep 10;9(9):e107509. doi: 10.1371/journal.pone.0107509. eCollection 2014.
The ubiquitination levels of protein substrates in eukaryotic cells are delicately orchestrated by various protein cofactors and enzymes. Dendritic cell-derived ubiquitin (Ub)-like protein (DC-UbP), also named as Ub domain-containing protein 2 (UBTD2), is a potential Ub shuttle protein comprised of a Ub-like (UbL) domain and a Ub-binding domain (UBD), but its biological function remains largely unknown. We identified two Ub-related enzymes, the deubiquitinating enzyme USP5 and the Ub-activating enzyme UbE1, as interacting partners of DC-UbP from HEK 293T cells. Biochemical studies revealed that the tandem UBA domains of USP5 and the C-terminal Ub-fold domain (UFD) of UbE1 directly interacted with the C-terminal UbL domain of DC-UbP but on the distinct surfaces. Overexpression of DC-UbP in HEK 293T cells enhanced the association of these two enzymes and thus prompted cellular ubiquitination, whereas knockdown of the protein reduced the cellular ubiquitination level. Together, DC-UbP may integrate the functions of USP5 and UbE1 through interacting with them, and thus reconcile the cellular ubiquitination and deubiquitination processes.
真核细胞中蛋白质底物的泛素化水平由多种蛋白质辅助因子和酶精心调控。树突状细胞衍生的类泛素（Ub）蛋白（DC-UbP），也称为含Ub结构域蛋白2（UBTD2），是一种潜在的Ub穿梭蛋白，由一个类Ub（UbL）结构域和一个Ub结合结构域（UBD）组成，但其生物学功能仍 largely未知。我们从HEK 293T细胞中鉴定出两种与Ub相关的酶，去泛素化酶USP5和Ub激活酶UbE1，作为DC-UbP的相互作用伴侣。生化研究表明，USP5的串联UBA结构域和UbE1的C末端Ub折叠结构域（UFD）直接与DC-UbP的C末端UbL结构域相互作用，但作用于不同的表面。在HEK 293T细胞中过表达DC-UbP增强了这两种酶的结合，从而促进了细胞泛素化，而敲低该蛋白则降低了细胞泛素化水平。总之，DC-UbP可能通过与USP5和UbE1相互作用来整合它们的功能，从而协调细胞泛素化和去泛素化过程。
