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The RanBP2 SUMO E3 ligase is neither HECT- nor RING-type
Andrea Pichler1, Puck Knipscheer, Hisato Saitoh
1Max-Planck Institute for Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany.
Nature Structural & Molecular Biology
|September 21, 2004
Summary
The SUMO E3 ligase RanBP2, unlike other ligases, functions through an unstructured catalytic fragment. It alters the E2 enzyme Ubc9
Area of Science:
- Biochemistry
- Molecular Biology
- Cellular Biology
Background:
- Post-translational modification by SUMO1 is crucial for cellular processes.
- SUMOylation requires E1 (Aos1-Uba2) and E2 (Ubc9) enzymes.
- E3 ligases enhance SUMOylation specificity and efficiency.
Purpose of the Study:
- To characterize the SUMO E3 ligase RanBP2 (Nup358).
- To elucidate the mechanism of RanBP2 in SUMOylation.
- To differentiate RanBP2 from other known E3 ligases.
Main Methods:
- Biochemical assays to assess SUMOylation activity.
- Analysis of RanBP2's catalytic fragment structure.
- Site-directed mutagenesis to identify key amino acid residues.
- Protein binding studies (stoichiometry).
Main Results:
- RanBP2's catalytic fragment is largely unstructured.
- Two distinct, partially overlapping catalytic domains exist in RanBP2.
- RanBP2 binds Ubc9 with a 1:1 stoichiometry.
- Specific RanBP2 and Ubc9 residues are critical for SUMOylation, involving hydrophobic interactions.
Conclusions:
- RanBP2 represents a novel class of SUMO E3 ligases.
- RanBP2's mechanism likely involves modulating Ubc9's properties.
- RanBP2's unique structure and function distinguish it from RING- and HECT-type E3 ligases.