Sumo-dependent substrate targeting of the SUMO protease Ulp1

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• The essential SUMO protease Ulp1 in yeast removes SUMO/Smt3 from targets and processes SUMO precursors.
• Ulp1 primarily localizes to nuclear pore complexes but also deconjugates sumoylated septins at the bud neck.
• Mechanisms directing Ulp1 to cytoplasmic targets like septins remain unclear.

Purpose of the Study:

• To elucidate structural features of Ulp1 essential for substrate targeting.
• To understand how Ulp1 is directed to cytoplasmic targets such as septins.
• To develop tools for purifying SUMO-modified proteins.

Main Methods:

• Structure/function analysis of Ulp1 mutants.
• Utilizing a catalytically inactive Ulp1 mutant enriched at the septin ring.
• Biochemical purification of SUMO-modified proteins using a substrate-trapping mutant.

Main Results:

• Ulp1 localization to septins requires SUMO and specific structural elements within its catalytic domain.
• A 218-amino acid substrate-trapping mutant, Ulp1(3)(C580S), is necessary and sufficient for septin localization.
• Ulp1(3)(C580S) was used to purify Smt3-modified proteins from yeast extracts.

Conclusions:

• Novel insights into the active targeting of Ulp1 SUMO protease to substrates in vivo and in vitro.
• The Ulp1(3)(C580S) mutant robustly interacts with human SUMO proteins and chains.
• Ulp1(3)(C580S) shows potential as a tool for analyzing and purifying SUMO-modified proteins.