DESI1

DESI1 (DeSI-1/PPPDE2) is a SUMO-specific isopeptidase that defines a class of deSUMOylating enzymes mechanistically and substrate-distinct from the SENP family (PMID:22370726). It removes SUMO, but not ubiquitin, from the transcriptional repressor BZEL, and unlike SENPs does not act on the substrates PML or ΔNp63, establishing that DeSI and SENP enzymes recognize separate substrate sets (PMID:22370726). Structurally, DESI1 functions as a homodimer in which the groove at the subunit interface forms the active site, built around a conserved cysteine–histidine catalytic dyad; consistent with its dedicated isopeptidase role it shows only minimal endopeptidase activity toward SUMO precursors, again contrasting with SENPs (PMID:22498933). Through its catalytic activity DESI1 is required for faithful chromosome segregation: its loss accelerates mitotic progression and increases segregation errors, and rescue by wild-type but not catalytically inactive enzyme shows the isopeptidase function is essential; mechanistically DESI1 sustains FoxM1-dependent transcription of Aurora B, cyclin B1, and CENP-F, supporting Aurora B chromosomal localization and spindle assembly checkpoint integrity (PMID:39698932). Beyond deSUMOylation, DESI1 additionally exhibits cysteine palmitoyl thioesterase (S-depalmitoylation) activity attributed to its N1pC/P60-type catalytic domain (PMID:35427157).

1. 2012 High

   Established that DESI1 is a SUMO protease of a previously unrecognized class, answering whether SUMO removal is restricted to the SENP family.

   Evidence In vitro deSUMOylation versus deubiquitination assays using BZEL, PML, and ΔNp63 substrates

   PMID:22370726

   Open questions at the time

   • Substrate repertoire beyond BZEL not defined
   • Physiological consequences of BZEL deSUMOylation not established
   • No cellular or in vivo validation in this study
2. 2012 High

   Defined the catalytic architecture, showing the active site forms at a homodimer interface around a Cys-His dyad and that DESI1 is a poor SUMO maturation enzyme, distinguishing it mechanistically from SENPs.

   Evidence X-ray crystallography with structure-guided catalytic residue identification and in vitro SUMO-1/SUMO-2 precursor endopeptidase assay

   PMID:22498933

   Open questions at the time

   • No substrate-bound structure to explain specificity
   • Mechanism of substrate selection over SENP substrates unresolved
3. 2022 Medium

   Expanded the catalytic repertoire by showing DESI1 also has S-depalmitoylation (thioesterase) activity, raising the possibility of a dual-activity enzyme.

   Evidence In vitro fluorescent substrate thioesterase assay with crystal structure and mutational analysis, as a secondary finding in a CLN5-focused study

   PMID:35427157

   Open questions at the time

   • DESI1/PPPDE2 thioesterase activity lacks dedicated mutagenesis validation for this paralog
   • No cellular palmitoylation substrate identified
   • Relationship between deSUMOylase and thioesterase activities unknown
4. 2024 Medium

   Connected DESI1 catalytic activity to a cellular function, demonstrating it is required for faithful chromosome segregation through FoxM1-dependent Aurora B expression and spindle assembly checkpoint function.

   Evidence siRNA knockdown with wild-type versus catalytic-dead rescue, nocodazole arrest, Aurora B immunofluorescence, and FoxM1 target gene RT-qPCR/western blot

   PMID:39698932

   Open questions at the time

   • Direct SUMO substrate linking DESI1 to FoxM1 not identified
   • Whether FoxM1 itself is a DESI1 substrate unresolved
   • Single-lab finding without independent replication
5. 2024 Low

   Confirmed DESI1 has a reactive, probe-accessible active-site cysteine in cells, relevant for chemical-biology targeting.

   Evidence Proteomic target engagement with activity-based probes (IMP-2587/IMP-2586) as an incidental finding in a USP30-focused study

   PMID:38725909

   Open questions at the time

   • Single incidental proteomics observation with no dedicated DESI1 follow-up
   • Functional consequence of probe engagement unknown
   • Selectivity of probes for DESI1 not characterized

• The full substrate spectrum of DESI1 and how its deSUMOylase versus depalmitoylase activities are coordinated to control mitosis remain unresolved.
• No direct deSUMOylation substrate connecting DESI1 to the FoxM1/Aurora B axis
• Physiological palmitoylation substrates unidentified
• No in vivo loss-of-function phenotype reported