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Updated: May 10, 2025

Visualization and Quantification of Endogenous Intra-Organelle Protein Interactions at ER-Mitochondria Contact Sites by Proximity Ligation Assays
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Artificial ER-Mitochondrion Tethering Restores Erg6 Localization and Lipid Droplet Formation in Hansenula polymorpha

Haiqiong Chen1, Rinse de Boer1, David C Lamb2

  • 1Molecular Cell Biology, Groningen Biomolecular Sciences and Biotechnology Institute, University of Groningen, Groningen, The Netherlands.

Contact (Thousand Oaks (Ventura County, Calif.))
|April 28, 2025
PubMed

Insights

Pex23 and Pex29 proteins are crucial for maintaining normal mitochondrial structure and lipid droplet numbers in yeast. Their absence causes the lipid droplet protein Erg6 to mislocalize to mitochondria.

Area of Science:

  • Cell Biology
  • Molecular Biology
  • Biochemistry

Background:

  • Pex23 proteins are fungal endoplasmic reticulum proteins.
  • Hansenula polymorpha has four Pex23 members; Pex24 and Pex32 are known to function at endoplasmic reticulum-peroxisome contact sites.
  • Absence of Pex23 and Pex29 leads to mitochondrial fragmentation and reduced lipid droplet numbers.

Purpose of the Study:

  • To investigate the function of Pex23 and Pex29 in Hansenula polymorpha.
  • To determine the role of Pex23 and Pex29 in regulating mitochondrial morphology and lipid droplet homeostasis.
  • To elucidate the mechanism by which Pex23 and Pex29 prevent mislocalization of specific proteins.

Main Methods:

  • Gene deletion studies (Δpex23, Δpex29) in Hansenula polymorpha.
  • Microscopy to assess mitochondrial morphology and lipid droplet numbers.
  • Immunofluorescence to track protein localization (Erg6).
  • Analysis of sterol composition.

Main Results:

  • In Δpex23 and Δpex29 cells, Erg6 (involved in ergosterol biosynthesis) mislocalizes to mitochondria.
  • Mitochondrial mislocalization of Erg6 and reduced lipid droplet numbers are suppressed by an artificial ER-mitochondrion tether.
  • Erg6 presence at mitochondria does not significantly alter overall sterol composition.

Conclusions:

  • Pex23 and Pex29 are essential for maintaining endoplasmic reticulum-mitochondrion contact sites.
  • These contact sites prevent the aberrant mitochondrial localization of the lipid droplet protein Erg6.
  • Pex23 and Pex29 play a critical role in cellular homeostasis by regulating protein trafficking between organelles.
Keywords:
Erg6Pex23Pex29lipid dropletmembrane contact sitesmitochondria

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