Hydrophobic ligand binding properties of the human lipocalin apolipoprotein M
Author
Summary, in English
Apolipoprotein M (apoM) is a plasma protein associated mainly with HDL. ApoM is suggested to be important for the formation of pre beta-HDL, but its mechanism of action is unknown. Homology modeling has suggested apoM to be a lipocalin. Lipocalins share a structurally conserved beta-barrel, which in many lipocalins bind hydrophobic ligands. The aim of this study was to test the ability of apoM to bind different hydrophobic substances. ApoM was produced both in Escherichia coli and in HEK 293 cells. Characterization of both variants with electrophoretic and immunological methods suggested apoM from E. coli to be correctly folded. Intrinsic tryptophan fluorescence of both apoM variants revealed that retinol, all-trans-retinoic acid, and 9-cis-retinoic acid bound ( dissociation constant 5 2-3 mu M), whereas other tested substances ( e.g., cholesterol, vitamin K, and arachidonic acid) did not. The intrinsic fluorescence of two apoM mutants carrying single tryptophans was quenched by retinol and retinoic acid to the same extent as wild-type apoM, indicating that the environment of both tryptophans was affected by the binding. In conclusion, the binding of retinol and retinoic acid supports the hypothesis that apoM is a lipocalin. The physiological relevance of this binding has yet to be elucidated.
Department/s
Publishing year
2007
Language
English
Pages
1754-1762
Publication/Series
Journal of Lipid Research
Volume
48
Issue
8
Document type
Journal article
Publisher
American Society for Biochemistry and Molecular Biology
Topic
- Medicinal Chemistry
Keywords
- cholesterol
- signal peptide
- lipoprotein
- high density
- intrinsic fluorescence
- retinol
- retinoic acid
Status
Published
Research group
- Clinical Chemistry, Malmö
ISBN/ISSN/Other
- ISSN: 1539-7262