Lysine 63-linked polyubiquitin chain may serve as a targeting signal for the 26S proteasome

• Published in: The EMBO journal Vol. 28; no. 4; pp. 359 - 371
• Main Authors: Saeki, Yasushi, Kudo, Tai, Sone, Takayuki, Kikuchi, Yoshiko, Yokosawa, Hideyoshi, Toh-e, Akio, Tanaka, Keiji
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 18.02.2009; Nature Publishing Group UK; Springer Nature B.V; Nature Publishing Group
• Subjects: Cellular biology; Cyclin-Dependent Kinase Inhibitor Proteins; Endosomal Sorting Complexes Required for Transport; Lysine - chemistry; Mass spectrometry; Mass Spectrometry - methods; Membrane Proteins; Models, Biological; Molecular biology; p120 GTPase Activating Protein - metabolism; Plasmids - metabolism; Polyubiquitin - chemistry; proteasome; Proteasome Endopeptidase Complex - metabolism; proteolysis; Saccharomyces cerevisiae - metabolism; Saccharomyces cerevisiae Proteins - metabolism; Signal Transduction; Substrates; Trans-Activators - metabolism; Transcription Factors; ubiquitin; Ubiquitin - chemistry; Ubiquitin-Protein Ligase Complexes - metabolism; yeast; Yeasts; proteasome; mass spectrometry; proteolysis; ubiquitin; yeast
• ISSN: 0261-4189; 1460-2075; 1460-2075
• DOI: 10.1038/emboj.2008.305

Recruitment of substrates to the 26S proteasome usually requires covalent attachment of the Lys48‐linked polyubiquitin chain. In contrast, modifications with the Lys63‐linked polyubiquitin chain and/or monomeric ubiquitin are generally thought to function in proteasome‐independent cellular processes. Nevertheless, the ubiquitin chain‐type specificity for the proteasomal targeting is still poorly understood, especially in vivo . Using mass spectrometry, we found that Rsp5, a ubiquitin‐ligase in budding yeast, catalyzes the formation of Lys63‐linked ubiquitin chains in vitro . Interestingly, the 26S proteasome degraded well the Lys63‐linked ubiquitinated substrate in vitro . To examine whether Lys63‐linked ubiquitination serves in degradation in vivo , we investigated the ubiquitination of Mga2‐p120, a substrate of Rsp5. The polyubiquitinated p120 contained relatively high levels of Lys63‐linkages, and the Lys63‐linked chains were sufficient for the proteasome‐binding and subsequent p120‐processing. In addition, Lys63‐linked chains as well as Lys48‐linked chains were detected in the 26S proteasome‐bound polyubiquitinated proteins. These results raise the possibility that Lys63‐linked ubiquitin chain also serves as a targeting signal for the 26S proteaseome in vivo .