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A conserved cysteine is essential for Pex4p-dependent ubiquitination of the peroxisomal import receptor Pex5p

Chris Williams1, Marlene van den Berg, Richard R Sprenger

  • 1Department of Medical Biochemistry, Academic Medical Center, Meibergdreef 15, 1105 AZ Amsterdam, The Netherlands.

The Journal of Biological Chemistry
|June 7, 2007
PubMed

Insights

The peroxisomal protein import receptor Pex5p undergoes ubiquitination via Ubc4p and Pex4p (Ubc10p). Pex4p-dependent ubiquitination targets a cysteine residue, crucial for Pex5p function, unlike Ubc4p-dependent modification of lysine residues.

Area of Science:

  • Cell Biology
  • Protein Biochemistry

Background:

  • Peroxisomal protein import receptor Pex5p is essential for cellular function.
  • Pex5p undergoes ubiquitination, a post-translational modification impacting protein function.
  • Ubiquitination can be mediated by different ubiquitin-conjugating enzymes (E2s).

Purpose of the Study:

  • To elucidate the distinct mechanisms and targets of Ubc4p-dependent and -independent ubiquitination of Pex5p.
  • To identify the specific ubiquitin-conjugating enzyme involved in Ubc4p-independent Pex5p ubiquitination.
  • To determine the functional significance of different ubiquitination sites on Pex5p.

Main Methods:

  • Investigated ubiquitination of Pex5p using Ubc4p and Pex4p (Ubc10p).
  • Analyzed ubiquitination sites by targeting specific residues in the N-terminal region of Pex5p.
  • Utilized beta-mercaptoethanol to assess the nature of ubiquitin-Pex5p linkages.

Main Results:

  • Identified Pex4p (Ubc10p) as the E2 enzyme for Ubc4p-independent Pex5p ubiquitination.
  • Demonstrated that Ubc4p-dependent ubiquitination occurs on lysine residues.
  • Showed Pex4p-dependent ubiquitination does not require lysine residues but involves a critical cysteine residue.
  • Observed that Pex4p-modified Pex5p is sensitive to beta-mercaptoethanol, suggesting modification on a cysteine residue.

Conclusions:

  • Pex4p-dependent ubiquitination of Pex5p occurs on a cysteine residue, distinct from lysine modification by Ubc4p.
  • This cysteine-mediated ubiquitination is essential for the overall function of Pex5p.
  • The findings reveal novel insights into the regulation of peroxisomal protein import via specific ubiquitination events.

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