title: The yeast Hex3.Slx8 heterodimer is a ubiquitin ligase stimulated by substrate sumoylation.
abstract: Hex3 and Slx8 are Saccharomyces cerevisiae proteins with important functions in DNA damage control and maintenance of genomic stability. Both proteins have RING domains at their C termini. Such domains are common in ubiquitin and ubiquitin-like protein ligases (E3s), but little was known about the molecular functions of either protein. In this study we identified HEX3 as a high-copy suppressor of a temperature-sensitive small ubiquitin-related modifier (SUMO) protease mutant, ulp1ts, suggesting that it may affect cellular SUMO dynamics. Remarkably, even a complete deletion of ULP1 is strongly suppressed. Hex3 forms a heterodimer with Slx8. We found that the Hex3.Slx8 complex has a robust substrate-specific E3 ubiquitin ligase activity. In this E3 complex, Slx8 appears to bear the core ligase function, with Hex3 strongly enhancing its activity. Notably, SUMO attachment to a substrate stimulates its Hex3.Slx8-dependent ubiquitination, primarily through direct noncovalent interactions between SUMO and Hex3. Our data reveal a novel mechanism of substrate targeting in which sumoylation of a protein can help trigger its subsequent ubiquitination by recruiting a SUMO-binding ubiquitin ligase.
authors.affiliation: Department of Molecular Biophysics and Biochemistry, Yale University, 266 Whitney Avenue, New Haven, CT 06520-8114, USA.
authors.forename: Yang
authors.initials: Y
authors.lastname: Xie
authors.forename: Oliver
authors.initials: O
authors.lastname: Kerscher
authors.forename: Mary B
authors.initials: MB
authors.lastname: Kroetz
authors.forename: Heather F
authors.initials: HF
authors.lastname: McConchie
authors.forename: Patrick
authors.initials: P
authors.lastname: Sung
authors.forename: Mark
authors.initials: M
authors.lastname: Hochstrasser
mesh_terms: D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism; D004249:DNA Damage / Q000502:physiology; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017353:Gene Deletion; D042822:Genomic Instability / Q000502:physiology; D046912:Multiprotein Complexes / Q000235:genetics / Q000378:metabolism*; D054829:RING Finger Domains / Q000502:physiology; D025842:SUMO-1 Protein / Q000235:genetics / Q000378:metabolism; D012441:Saccharomyces cerevisiae / Q000201:enzymology* / Q000235:genetics; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*; D013379:Substrate Specificity / Q000502:physiology; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism; D044767:Ubiquitin-Protein Ligases / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination / Q000235:genetics
chemical_list: D004268:DNA-Binding Proteins; D046912:Multiprotein Complexes; D025842:SUMO-1 Protein; D029701:Saccharomyces cerevisiae Proteins; D025801:Ubiquitin; C515574:Slx8 protein, S cerevisiae; D044767:Ubiquitin-Protein Ligases; D003546:Cysteine Endopeptidases; C118083:Ulp1 protease; C515573:Slx5 protein, S cerevisiae