Cdc5-mediated Ulp2 phosphorylation controls the timing of polySUMOylation during the cell cycle

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• SUMOylation is a crucial posttranslational modification regulating protein function and localization.
• PolySUMOylation, a chain-like SUMOylation, plays a role in cell cycle progression.
• SUMO proteases, like Ulp2, are essential for regulating SUMOylation levels.

Purpose of the Study:

• To investigate the role of mitotic kinase Cdc5 in regulating polySUMOylation.
• To elucidate the mechanism by which Ulp2 activity is controlled during the cell cycle.
• To identify the specific phosphorylation events on Ulp2 that influence its function.

Main Methods:

• Yeast genetics and molecular biology techniques were employed.
• Site-directed mutagenesis was used to create phosphodeficient Ulp2 mutants (ulp2S734A).
• Protein interaction assays and biochemical analyses were performed.

Main Results:

• Cdc5 kinase activity is necessary for protein polySUMOylation.
• Phosphorylation of Ulp2 at serine 734 by Cdc5 reduces its affinity for SUMO chains.
• The phosphodeficient ulp2S734A mutant suppressed polySUMOylation induced by Cdc5 overexpression or Rts1 deletion.
• PP2A-Rts1 phosphatase counteracts Cdc5-mediated phosphorylation of Ulp2.

Conclusions:

• Cdc5-dependent phosphorylation of Ulp2 at Ser734 is a key regulatory step that promotes polySUMOylation by decreasing Ulp2's SUMO chain binding affinity.
• PP2A-Rts1 acts as a negative regulator, preventing premature polySUMOylation by dephosphorylating Ulp2.
• This intricate phosphorylation-dephosphorylation balance ensures proper control of polySUMOylation during cell cycle progression.