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In Vitro Analysis of E3 Ubiquitin Ligase Function
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A Residue Specific Insight into the Arkadia E3 Ubiquitin Ligase Activity and Conformational Plasticity
Maria Birkou1, Christos T Chasapis1, Konstantinos D Marousis1
1Department of Pharmacy, University of Patras, GR-26504 Patras, Greece.
Journal of Molecular Biology
|June 26, 2017
Summary
Arkadia E3 ligase amplifies TGF-β signaling by degrading pathway inhibitors. A key tryptophan (W972) mutation (W972A) retained function, while another (W972R) lost it due to impaired E2 enzyme interaction and structural changes.
Area of Science:
- Biochemistry
- Molecular Biology
- Cell Signaling
Background:
- Arkadia (Rnf111) is an E3 ubiquitin ligase crucial for transforming growth factor beta (TGF-β) signaling.
- It amplifies TGF-β responses by degrading negative regulators like Smad6, Smad7, Ski, and Skil (SnoN).
- Arkadia's function relies on its Really Interesting New Gene (RING)-H2 domain interacting with the E2 enzyme UbcH5b.
Purpose of the Study:
- To investigate the structural and dynamic roles of a conserved tryptophan (W972) in the Arkadia RING-H2 domain.
- To elucidate the functional differences between W972A (functional) and W972R (non-functional) Arkadia mutants.
Main Methods:
- Nuclear Magnetic Resonance (NMR) spectroscopy to analyze structural and dynamical properties of Arkadia mutants.
- In vivo functional assays using a TGF-β-responsive promoter driving luciferase expression.
- Assessment of E2 enzyme (UbcH5b) interaction with Arkadia mutants.
Main Results:
- The W972A Arkadia mutant exhibited wild-type (WT) activity in enhancing TGF-β signaling.
- The W972R Arkadia mutant showed a significant loss of function.
- W972A displayed minor structural differences from WT-Arkadia, while W972R showed impaired E2 interaction, altered C-terminal α-helix structure, and increased Zn(II) ion distance.
Conclusions:
- The W972 residue in Arkadia's RING domain is critical for its E3 ligase activity and E2 enzyme recruitment.
- The specific residue at position 972 dictates Arkadia's functional outcome, with alanine supporting function and arginine abolishing it.
- Structural integrity of the C-terminal α-helix and proper Zn(II) coordination are essential for Arkadia's enzymatic activity.
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