Piterman Ravit, Braunstein Ilana, Isakov Elada, Ziv Tamar, Navon Ami, Cohen Shenhav, Stanhill Ariel
Department of Biochemistry, Rappaport Family Institute for Research in the Medical Sciences, Technion-Israel Institute of Technology, Haifa 31096, Israel.
Smoler Proteomics Center, Technion-Israel Institute of Technology, Haifa 32000, Israel.
Mol Biol Cell. 2014 Dec 15;25(25):3988-98. doi: 10.1091/mbc.E13-11-0697. Epub 2014 Oct 15.
The 26S proteasome recognizes a vast number of ubiquitin-dependent degradation signals linked to various substrates. This recognition is mediated mainly by the stoichiometric proteasomal resident ubiquitin receptors S5a and Rpn13, which harbor ubiquitin-binding domains. Regulatory steps in substrate binding, processing, and subsequent downstream proteolytic events by these receptors are poorly understood. Here we demonstrate that mammalian S5a is present in proteasome-bound and free states. S5a is required for efficient proteasomal degradation of polyubiquitinated substrates and the recruitment of ubiquitin-like (Ubl) harboring proteins; however, S5a-mediated ubiquitin and Ubl binding occurs only on the proteasome itself. We identify the VWA domain of S5a as a domain that limits ubiquitin and Ubl binding to occur only upon proteasomal association. Multiubiquitination events within the VWA domain can further regulate S5a association. Our results provide a molecular explanation to how ubiquitin and Ubl binding to S5a is restricted to the 26S proteasome.
26S蛋白酶体可识别大量与各种底物相连的泛素依赖性降解信号。这种识别主要由化学计量的蛋白酶体驻留泛素受体S5a和Rpn13介导，它们含有泛素结合结构域。这些受体在底物结合、加工以及随后的下游蛋白水解事件中的调控步骤尚不清楚。在此，我们证明哺乳动物的S5a以与蛋白酶体结合和游离两种状态存在。S5a是多聚泛素化底物有效蛋白酶体降解以及募集含泛素样（Ubl）蛋白所必需的；然而，S5a介导的泛素和Ubl结合仅发生在蛋白酶体自身上。我们确定S5a的VWA结构域是一个仅在蛋白酶体结合时才限制泛素和Ubl结合发生的结构域。VWA结构域内的多聚泛素化事件可进一步调节S5a的结合。我们的结果为泛素和Ubl与S5a的结合如何局限于26S蛋白酶体提供了分子解释。
