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Updated: Jul 10, 2026

Isolation and Analysis of Plasma Lipoproteins by Ultracentrifugation
06:47

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Published on: January 28, 2021

ApoJ regulates endothelial lipase activity and stability.

Uriel L Jean-Baptiste1, Simcha R Singh1, Ming J Wu1

  • 1Department of Biochemistry and Biophysics, The University of North Carolina Chapel Hill, Chapel Hill, North Carolina, USA.

Protein Science : a Publication of the Protein Society
|March 3, 2026
PubMed
Summary

Apolipoprotein J (ApoJ) acts as a chaperone for endothelial lipase (EL), enhancing its activity and solubility. This discovery clarifies EL function in high-density lipoprotein (HDL) metabolism.

Keywords:
apolipoprotein Jchaperoneclusterinendothelial lipasehepatic lipasehigh‐density lipoproteinlipoprotein lipaselipoprotein metabolismpancreatic lipase

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Area of Science:

  • Lipid metabolism
  • Protein biochemistry
  • Molecular biology

Background:

  • Endothelial lipase (EL) is crucial for high-density lipoprotein (HDL) metabolism.
  • Understanding EL function is limited by difficulties in purifying active EL.

Purpose of the Study:

  • Identify novel factors influencing EL solubility and activity.
  • Elucidate the role of apolipoprotein J (ApoJ) in EL function.

Main Methods:

  • Developed an optimized protocol for active EL purification.
  • Investigated ApoJ-EL interaction using protein co-purification and mutagenesis.
  • Assessed EL activity in vitro and in vivo (mouse plasma).
  • Utilized knockdown experiments to evaluate ApoJ's effect on EL activity.

Main Results:

  • Apolipoprotein J (ApoJ) was identified as a novel chaperone for endothelial lipase (EL).
  • ApoJ consistently co-purifies with active EL, maintaining its solubility and enzymatic activity.
  • Mutagenesis of specific ApoJ regions (hydrophobic lid, tryptophan loop) abolished its effect on EL.
  • ApoJ enhances EL activity by acting as a chaperone, not a direct carrier to HDL particles.

Conclusions:

  • ApoJ is essential for EL solubility and activity, functioning as a chaperone.
  • ApoJ protects EL in plasma and enhances its hydrolysis of lipoprotein substrates.
  • This interaction provides new insights into HDL metabolism and suggests ApoJ as an accessory protein for EL.