A new protease required for cell-cycle progression in yeast.

Area of Science:

• Biochemistry
• Molecular Biology
• Cell Biology

Background:

• Protein function in eukaryotes is regulated by conjugation to ubiquitin or ubiquitin-like proteins (Ubls).
• SUMO-1 (vertebrate) and Smt3 (yeast) are Ubl proteins involved in numerous physiological processes.
• The essentiality of deconjugation for SUMO-1/Smt3 pathways was previously unknown.

Purpose of the Study:

• To identify and characterize proteases involved in the deconjugation of Smt3 and SUMO-1.
• To investigate the cellular functions and conservation of such proteases.

Main Methods:

• Identification and characterization of a yeast Ubl-specific protease, Ulp1.
• Assay of Ulp1 activity against Smt3, SUMO-1, and ubiquitin conjugates.
• Analysis of Ulp1 homologues in various organisms.
• Investigation of Smt3-conjugated proteins and cell cycle progression in yeast ulp1 mutants.

Main Results:

• Ulp1 specifically cleaves Smt3 and SUMO-1, but not ubiquitin, from conjugated proteins.
• Ulp1 is a novel Ubl-specific protease, unrelated to known deubiquitinating enzymes, but shares distant similarity with viral proteases.
• Ulp1 homologues are conserved across many organisms, including human pathogens.
• Smt3 conjugation patterns in yeast vary with the cell cycle, and specific conjugates accumulate in ulp1 mutants.
• Ulp1 plays an essential role in the G2/M phase of the cell cycle.

Conclusions:

• Ulp1 is a key enzyme in the deconjugation of Smt3/SUMO-1, essential for protein regulation and cellular processes.
• The discovery of Ulp1 indicates a conserved protease family involved in Ubl pathways.
• Ulp1's role in the cell cycle highlights the importance of SUMOylation/deSUMOylation dynamics in cell division.