The RanBP2/RanGAP1*SUMO1/Ubc9 SUMO E3 ligase is a disassembly machine for Crm1-dependent nuclear export complexes

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Continuous nucleocytoplasmic transport necessitates the disassembly of transport receptor/Ran-GTP complexes in the cytoplasm.
• A fundamental disassembly mechanism across eukaryotes involves soluble RanGAP and RanBP1.
• In vertebrates, RanGAP1 often stably associates with the nucleoporin RanBP2.

Purpose of the Study:

• To investigate the function of the RanBP2/RanGAP1*SUMO1/Ubc9 complex as a disassembly machine.
• To elucidate the mechanism by which this complex disassembles transport receptor complexes, particularly Crm1.
• To explore potential links between Crm1 disassembly and SUMO-dependent functions.

Main Methods:

• In vitro reconstitution of the RanBP2/RanGAP1*SUMO1/Ubc9 complex.
• Biochemical assays to analyze the disassembly of Crm1 export complexes.
• Characterization of disassembly intermediates using structural and binding analyses.

Main Results:

• The RanBP2/RanGAP1*SUMO1/Ubc9 complex functions as an autonomous disassembly machine with a preference for the export receptor Crm1.
• Three distinct in vitro reconstituted disassembly intermediates were identified, detailing Crm1 binding, cargo release, and retention.
• All observed intermediates were compatible with SUMO E3 ligase activity.

Conclusions:

• The RanBP2/RanGAP1*SUMO1/Ubc9 complex efficiently disassembles Crm1 export complexes.
• The findings suggest a potential mechanistic link between Crm1-dependent nucleocytoplasmic transport and SUMOylation pathways.