Proximity Proteomics and Biochemical Analysis Reveal a Noncanonical Function for UFM1-Specific Protease 1 in the p62 Body Formation

Protein aggregates play crucial rolesin the development of neurodegenerativediseases and p62 is one of the key proteins regulating the formationof protein aggregates. Recently, it has been discovered that depletionof several key enzymes including UFM1-activating enzyme UBA5, UFM1-conjugatingenzyme UFC1, UFM1-protein ligase UFL1, and UFM1-specific proteaseUfSP2 in the UFM1-conjugation system induces p62 accumulation to formp62 bodies in the cytosol. However, it is unknown whether UfSP1 participatesin the formation of p62 bodies and whether its enzymatic activityis required for this process. Here, the proximity labeling techniqueand quantitative proteomics identify SQSTM1/p62 as a UfSP1-interactingprotein. Coimmunoprecipitation reveals that p62 indeed interacts withUfSP1 and the immunofluorescence experiment discloses that UfSP1 colocalizeswith p62 and promotes the formation of p62-mediated protein aggregates.Mechanistic studies unveil that UfSP1 binds to the ubiquitin-associateddomain of p62 and promotes the interaction between p62 and ubiquitinatedproteins, thereby increasing the formation of p62 bodies. Interestingly,we further demonstrate that both the catalytic active and inactiveUfSP1 promote the formation of p62 bodies through the same mechanism.Taken together, this work discovers that UfSP1 exhibits a noncanonicalfunction independent of its protease activity in the p62 body formation.

Automated summary

Protein aggregates are important in the development of neurodegenerative diseases, with p62 being a key protein in regulating their formation. A recent discovery shows that the depletion of certain enzymes in the UFM1-conjugation system leads to the accumulation of p62 and the formation of p62 bodies. It is unclear if UfSP1 is involved in the formation of p62 bodies and if its enzymatic activity is required for this process.