Eckhoff Julia, Dohmen R Jürgen
From the Institute for Genetics, Biocenter, University of Cologne, D-50674 Cologne, Germany.
From the Institute for Genetics, Biocenter, University of Cologne, D-50674 Cologne, Germany
J Biol Chem. 2015 May 8;290(19):12268-81. doi: 10.1074/jbc.M114.622217. Epub 2015 Apr 1.
Sumoylation is a post-translational modification essential in most eukaryotes that regulates stability, localization, activity, or interaction of a multitude of proteins. It is a reversible process wherein counteracting ligases and proteases, respectively, mediate the conjugation and deconjugation of SUMO molecules to/from target proteins. Apart from attachment of single SUMO moieties to targets, formation of poly-SUMO chains occurs by the attachment of additional SUMO molecules to lysine residues in the N-terminal extensions of SUMO. In Saccharomyces cerevisiae there are apparently only two SUMO(Smt3)-specific proteases: Ulp1 and Ulp2. Ulp2 has been shown to be important for the control of poly-SUMO conjugates in cells and to dismantle SUMO chains in vitro, but the mechanism by which it acts remains to be elucidated. Applying an in vitro approach, we found that Ulp2 acts sequentially rather than stochastically, processing substrate-linked poly-SUMO chains from their distal ends down to two linked SUMO moieties. Furthermore, three linked SUMO units turned out to be the minimum length of a substrate-linked chain required for efficient binding to and processing by Ulp2. Our data suggest that Ulp2 disassembles SUMO chains by removing one SUMO moiety at a time from their ends (exo mechanism). Apparently, Ulp2 recognizes surfaces at or near the N terminus of the distal SUMO moiety, as attachments to this end significantly reduce cleavage efficiency. Our studies suggest that Ulp2 controls the dynamic range of SUMO chain lengths by trimming them from the distal ends.
SUMO化是大多数真核生物中一种重要的翻译后修饰，它调节众多蛋白质的稳定性、定位、活性或相互作用。这是一个可逆过程，其中相互作用的连接酶和蛋白酶分别介导SUMO分子与靶蛋白的结合与去结合。除了单个SUMO部分与靶标结合外，多聚SUMO链的形成是通过将额外的SUMO分子连接到SUMO N端延伸区的赖氨酸残基上实现的。在酿酒酵母中，显然只有两种SUMO（Smt3）特异性蛋白酶：Ulp1和Ulp2。Ulp2已被证明对细胞中多聚SUMO缀合物的控制很重要，并且在体外能拆解SUMO链，但其作用机制仍有待阐明。采用体外方法，我们发现Ulp2是按顺序而非随机作用的，从底物连接的多聚SUMO链的远端开始处理，直至剩下两个连接的SUMO部分。此外，三个连接的SUMO单元被证明是底物连接链有效结合Ulp2并被其处理所需的最小长度。我们的数据表明，Ulp2通过一次从链的末端去除一个SUMO部分来拆解SUMO链（外切机制）。显然，Ulp2识别远端SUMO部分N端或其附近的表面，因为连接到这个末端会显著降低切割效率。我们的研究表明，Ulp2通过从远端修剪SUMO链来控制SUMO链长度的动态范围。
