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E2 superfamily of ubiquitin-conjugating enzymes: constitutively active or activated through phosphorylation in the

Ilaria Valimberti1, Matteo Tiberti1, Matteo Lambrughi1

  • 1Department of Biotechnology and Biosciences, University of Milano-Bicocca, Piazza della Scienza 2, 20126, Milan (Italy).

Scientific Reports
|October 15, 2015
PubMed

Insights

Protein phosphorylation regulates cellular processes and ubiquitination. A conserved E2 serine/aspartate (CES/D) site in ubiquitin-conjugating enzymes controls ubiquitination efficiency and determines if E2 enzymes are constitutively active or regulated by phosphorylation.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Cellular Biology

Background:

  • Protein phosphorylation is a key regulator of cellular processes, with dysregulation linked to various diseases.
  • Phosphorylation is increasingly recognized for its role in modulating ubiquitination pathways.
  • The precise mechanisms by which phosphorylation influences ubiquitinating enzymes remain largely unknown.

Purpose of the Study:

  • To investigate the molecular mechanisms of how phosphorylation regulates ubiquitin-conjugating enzymes (E2s).
  • To identify and characterize a conserved functional site in E2 enzymes involved in activity regulation.
  • To elucidate the role of this conserved site in controlling ubiquitination efficiency.

Main Methods:

  • Utilized molecular simulations to analyze wild type, mutant, and phosphorylated E2 enzymes in substrate-bound and -unbound states.
  • Examined the structural and functional impact of the conserved E2 serine/aspartate (CES/D) site.
  • Analyzed the physicochemical properties (size and charge) of the residue at the CES/D site.

Main Results:

  • Identified a highly conserved functional site, the conserved E2 serine/aspartate (CES/D) site, in catalytically active E2 enzymes.
  • Demonstrated that the CES/D site's residue (aspartate or serine) and its properties are critical for optimal E2 activity.
  • Showed that the CES/D site's size and charge influence substrate lysine alignment, thereby controlling ubiquitination efficiency.
  • Proposed that E2 enzymes can be classified into constitutively active (aspartate at CES/D) or regulated (serine at CES/D) families.

Conclusions:

  • The CES/D site is a critical determinant of E2 enzyme activity and regulation.
  • E2 enzymes with aspartate at the CES/D site are constitutively active, while those with serine can be regulated by phosphorylation.
  • This finding provides a mechanistic basis for understanding how phosphorylation modulates ubiquitination and offers insights into disease-associated aberrant signaling.

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