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

ArticleinJournal of Biological Chemistry 283(29):19912-21 · August 2008with3 Reads
Impact Factor: 4.57 · DOI: 10.1074/jbc.M802690200 · Source: PubMed


    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.