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Comparative Strategies for Ubiquitination Detection in Mammalian Cell Lysates Using SMAD2/SMURF2 as a Model
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Auto-ubiquitination of Mdm2 enhances its substrate ubiquitin ligase activity

Ruchira S Ranaweera1, Xiaolu Yang

  • 1Department of Cancer Biology and Abramson Family Cancer Research Institute, Perelman School of Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19104, USA.

The Journal of Biological Chemistry
|May 15, 2013
PubMed

Insights

Mdm2 auto-ubiquitination activates its E3 ligase activity toward p53. Polyubiquitin chains on Mdm2 enhance E2 enzyme recruitment, boosting p53 degradation and supporting a model of enzyme autocatalysis.

Area of Science:

  • Molecular Biology
  • Biochemistry
  • Cancer Research

Background:

  • Mdm2 (mouse double minute 2) is a RING domain E3 ubiquitin ligase crucial for regulating the tumor suppressor p53.
  • Mdm2 targets p53 for proteasomal degradation, inhibiting its activity and promoting cell survival.
  • The impact of Mdm2 auto-ubiquitination on its enzymatic function remains largely uncharacterized.

Purpose of the Study:

  • To investigate the functional consequences of Mdm2 auto-ubiquitination.
  • To elucidate the mechanism by which Mdm2 auto-ubiquitination influences its E3 ligase activity.
  • To explore the role of ubiquitin chains in modulating E3 ligase activity.

Main Methods:

  • In vitro ubiquitination assays using purified Mdm2 and p53.
  • Site-directed mutagenesis to disrupt noncovalent interactions between Mdm2 and E2 enzymes.
  • Analysis of Mdm2 auto-ubiquitination status and its effect on p53 polyubiquitination.

Main Results:

  • Mdm2 auto-ubiquitination, specifically via polyubiquitin chains, significantly enhances its E3 ligase activity towards p53.
  • Auto-ubiquitination promotes the recruitment of E2 ubiquitin-conjugating enzymes through noncovalent interactions with ubiquitin chains.
  • Disruption of these noncovalent interactions abolishes the stimulatory effect of auto-ubiquitination on Mdm2 activity.

Conclusions:

  • Mdm2 auto-ubiquitination acts as an activating mechanism for its ligase function.
  • Polyubiquitin chains on E3 ligases can enhance E2 enzyme binding and processivity, suggesting a general regulatory principle.
  • Autocatalysis may be a common mechanism for activating latent E3 ubiquitin ligases.
Keywords:
Auto-ubiquitinationCancer BiologyMdm2UbiquitinUbiquitin LigaseUbiquitin-conjugating Enzyme (Ubc)Ubiquitinationp53

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