A new SUMO-1-specific protease, SUSP1, that is highly expressed in reproductive organs

A full-length cDNA encoding a SUlMO-1-specific protease, named SUSP1, was i dentified and cloned for the first time from the human brain. Nucleotide se quence analysis of the cDNA containing an open reading flame of 3336 base p airs revealed that the protease consists of 1112 amino acids with a calcula ted molecular mass of 126,116 Da. Like yeast Ulp1, SUSP1 is a cysteine prot ease containing the well conserved His/Asp/Cys catalytic triad. SUSP1 expre ssed in Escherichia coli cells efficiently released SUMO-1 from SUMO-1 . be ta-galactosidase fusion but not from other ubiquitin-like protein fusions, including Smt3 . beta-galactosidase, suggesting its role in the generation of matured SUMO-1 specifically from its precursors. Interestingly, reproduc tive organs, such as testis, ovary, and prostate, contained much higher amo unts of SUSP1 mRNA than colon and peripheral blood leukocyte, whereas other tissues, such as heart and spleen, had little or none. In addition, confoc al microscopy using green fluorescent protein SUSP1 fusion showed that SUSP 1 is exclusively localized to the cytoplasm of NIH3T3 and HeLa cells. These results suggest that SUSP1 may play a role in the regulation of SUMO-1-med iated cellular processes particularly related to reproduction.