Xu Ping, Duong Duc M, Seyfried Nicholas T, Cheng Dongmei, Xie Yang, Robert Jessica, Rush John, Hochstrasser Mark, Finley Daniel, Peng Junmin
Department of Human Genetics, Center for Neurodegenerative Diseases, Emory University, Atlanta, GA 30322, USA.
Cell. 2009 Apr 3;137(1):133-45. doi: 10.1016/j.cell.2009.01.041.
All seven lysine residues in ubiquitin contribute to the synthesis of polyubiquitin chains on protein substrates. Whereas K48-linked chains are well established as mediators of proteasomal degradation, and K63-linked chains act in nonproteolytic events, the roles of unconventional polyubiquitin chains linked through K6, K11, K27, K29, or K33 are not well understood. Here, we report that the unconventional linkages are abundant in vivo and that all non-K63 linkages may target proteins for degradation. Ubiquitin with K48 as the single lysine cannot support yeast viability, and different linkages have partially redundant functions. By profiling both the entire yeast proteome and ubiquitinated proteins in wild-type and ubiquitin K11R mutant strains using mass spectrometry, we identified K11 linkage-specific substrates, including Ubc6, a ubiquitin-conjugating enzyme involved in endoplasmic reticulum-associated degradation (ERAD). Ubc6 primarily synthesizes K11-linked chains, and K11 linkages function in the ERAD pathway. Thus, unconventional polyubiquitin chains are critical for ubiquitin-proteasome system function.
泛素中的所有七个赖氨酸残基都有助于在蛋白质底物上合成多聚泛素链。虽然K48连接的链作为蛋白酶体降解的介质已得到充分证实，而K63连接的链在非蛋白水解事件中起作用，但通过K6、K11、K27、K29或K33连接的非常规多聚泛素链的作用尚未得到充分了解。在这里，我们报告非常规连接在体内很丰富，并且所有非K63连接都可能将蛋白质靶向降解。以K48作为唯一赖氨酸的泛素不能支持酵母的生存能力，并且不同的连接具有部分冗余功能。通过使用质谱分析野生型和泛素K11R突变株中的整个酵母蛋白质组和泛素化蛋白质，我们鉴定了K11连接特异性底物，包括Ubc6，一种参与内质网相关降解（ERAD）的泛素结合酶。Ubc6主要合成K11连接的链，并且K11连接在内质网相关降解途径中起作用。因此，非常规多聚泛素链对于泛素-蛋白酶体系统功能至关重要。
