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Updated: Jul 14, 2026

Optimized Negative Staining: a High-throughput Protocol for Examining Small and Asymmetric Protein Structure by Electron Microscopy
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Published on: August 15, 2014

Hydrophobic ligand binding properties of the human lipocalin apolipoprotein M

Josefin Ahnström1, Kirsten Faber, Olof Axler

  • 1Department of Laboratory Medicine, Division of Clinical Chemistry, Lund University, University Hospital, SE-20502 Malmö, Sweden.

Journal of Lipid Research
|May 26, 2007
PubMed

Insights

Apolipoprotein M (apoM), a plasma protein, binds retinol and retinoic acid, supporting its role as a lipocalin. Further research is needed to understand the physiological relevance of this hydrophobic ligand binding.

Area of Science:

  • Biochemistry
  • Molecular Biology
  • Lipid Metabolism

Background:

  • Apolipoprotein M (apoM) is a plasma protein primarily associated with high-density lipoprotein (HDL).
  • Its precise mechanism in prebeta-HDL formation remains unknown.
  • Structural homology suggests apoM may function as a lipocalin, a class of proteins known to bind hydrophobic ligands.

Purpose of the Study:

  • To investigate the hydrophobic ligand-binding capabilities of apolipoprotein M.
  • To determine if apoM exhibits lipocalin-like properties by testing its interaction with various hydrophobic substances.

Main Methods:

  • Production of apolipoprotein M in Escherichia coli and HEK 293 cells.
  • Characterization using electrophoretic and immunological techniques.
  • Analysis of ligand binding via intrinsic tryptophan fluorescence spectroscopy, including studies with apoM mutants.

Main Results:

  • Recombinant apoM from E. coli was confirmed to be correctly folded.
  • Apolipoprotein M demonstrated binding to retinol, all-trans-retinoic acid, and 9-cis-retinoic acid with dissociation constants of 2-3 microM.
  • No significant binding was observed for cholesterol, vitamin K, or arachidonic acid.
  • Retinol and retinoic acid binding affected the tryptophan environment in apoM mutants.

Conclusions:

  • The binding of retinol and retinoic acid supports the hypothesis that apolipoprotein M functions as a lipocalin.
  • These findings provide new insights into the molecular interactions of apoM.
  • The physiological significance of apoM's interaction with these specific hydrophobic molecules requires further investigation.

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