Article

Activation of the Slx5–Slx8 Ubiquitin Ligase by Poly-small Ubiquitin-like Modifier Conjugates

Department of Molecular Biology and Biochemistry, Rutgers University, Piscataway, NJ 08854, USA.
Journal of Biological Chemistry (Impact Factor: 4.57). 08/2008; 283(29):19912-21. DOI: 10.1074/jbc.M802690200
Source: PubMed

ABSTRACT Protein sumoylation is a regulated process that is important for the health of human and yeast cells. In budding yeast, a subset of sumoylated proteins is targeted for ubiquitination by a conserved heterodimeric ubiquitin (Ub) ligase, Slx5-Slx8, which is needed to suppress the accumulation of high molecular weight small ubiquitin-like modifier (SUMO) conjugates. Structure-function analysis indicates that the Slx5-Slx8 complex contains multiple SUMO-binding domains that are collectively required for in vivo function. To determine the specificity of Slx5-Slx8, we assayed its Ub ligase activity using sumoylated Siz2 as an in vitro substrate. In contrast to unsumoylated or multisumoylated Siz2, substrates containing poly-SUMO conjugates were efficiently ubiquitinated by Slx5-Slx8. Although Siz2 itself was ubiquitinated, the bulk of the Ub was conjugated to SUMO residues. Slx5-Slx8 primarily mono-ubiquitinated the N-terminal SUMO moiety of the chain. These data indicate that the Slx5-Slx8 Ub ligase is stimulated by poly-SUMO conjugates and that it can ubiquitinate a poly-SUMO chain.

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    • "The best characterized S. cerevisiae STUbL is the heterodimer complex composed of two RING domain proteins Slx5 and Slx8 [11] [12] [13] [14] [15]. Slx8 shows an E3 ubiquitin ligase activity and interacts with an E2 ubiquitin conjugating enzyme Ubc4, while Slx5 binds to polysumoylated substrates via its multiple SIMs [11] [12]. Strains lacking SLX5/8 show many features of genomic instability, such as slow growth, increased sensitivity to genotoxins, gross chromosomal rearrangements, increased rates of chromosome loss and recombination [16] [17] [18] [19] [20] [21]. "
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    • "To test this hypothesis, we initially focused on the interaction of Slx5 with two known interactors, SUMO and Slx8 (Ii et al., 2007; Xie et al., 2007; Mullen and Brill, 2008)). "
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    • "A functional conservation of these proteins to yeast Sgs1 is indicated by the observation that the WRN and BLM genes can complement the hyper-recombination phenotype of sgs1 mutants [72]. Defects caused by the inactivation of SGS1 go along with an accumulation of HMW-SUMO conjugates suggesting that Slx5–Slx8 may have a function in promoting turnover of SUMO-modified proteins in the course of, or following DNA repair processes [66]. On the other Fig. 1. "
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