Minimal length requirement for proteasomal degradation of ubiquitin-dependent substrates

• Published in: The FASEB journal 2009, Vol.23 (1), p.123-133
• Main Authors: Verhoef, Lisette G.G.C, Heinen, Christian, Selivanova, Alexandra, Halff, Els F, Salomons, Florian A, Dantuma, Nico P
• Format: Article
• Language: English
• Subjects: Alzheimer; Amino Acid Sequence; Cell Line, Tumor; conformational diseases; Humans; Medicin och hälsovetenskap; Molecular Sequence Data; Mutation; neurodegen‐eration; Proteasome Endopeptidase Complex - metabolism; protein degradation; Saccharomyces cerevisiae - genetics; Saccharomyces cerevisiae - metabolism; Substrate Specificity; Transcription, Genetic; UBB+1; Ubiquitin - genetics; Ubiquitin - metabolism; ubiquitinfusion degradation
• ISSN: 0892-6638; 1530-6860; 1530-6860
• DOI: 10.1096/fj.08-115055

An erroneous transcriptional process, known as molecular misreading, gives rise to an alternative transcript of the ubiquitin B (UBB) gene. This transcript encodes the protein UBB⁺¹, which comprises a ubiquitin moiety and a 19-aa C-terminal extension. UBB⁺¹ is found in affected neurons in neurodegenerative diseases and behaves as an atypical ubiquitin fusion degradation (UFD) proteasome substrate that is poorly degraded and impedes the ubiquitin/proteasome system. Here, we show that the limited length of UBB⁺¹ is responsible for its inefficient degradation and inhibitory activity. Designed UFD substrates with an equally short 19-aa or a 20-aa C-terminal extension were also poorly degraded and had a general inhibitory activity on the ubiquitin/proteasome system in two unrelated cell lines. Extending the polypeptide to 25 aa sufficed to convert the protein into an efficiently degraded proteasome substrate that lacked inhibitory activity. A similar length dependency was found for degradation of two UFD substrates in Saccharomyces cerevisiae, which suggests that the mechanisms underlying this length constraint are highly conserved. Extending UBB⁺¹ also converted this protein into an efficient substrate of the proteasome. These observations provide an explanation for the accumulation of UBB⁺¹ in neurodegenerative disorders and offers new insights into the physical constraints determining proteasomal degradation.--Verhoef, L. G. G. C., Heinen, C., Selivanova, A., Halff, E. F., Salomons, F. A., Dantuma, N. P. Minimal length requirement for proteasomal degradation of ubiquitin-dependent substrates.