Serendipitous Fatty Acid Binding Reveals the Structural Determinants for Ligand Recognition in Apolipoprotein M
Author
Summary, in English
Apolipoprotein M (ApoM) is a 25-kDa HDL-associated apolipoprotein and a member of the lipocalin family of proteins. Mature apoM retains its signal peptide, which serves as a lipid anchor attaching apoM to the lipoproteins, thereby keeping it in the circulation. Studies in mice have suggested apoM to be antiatherogenic, but its physiological function is yet unknown. We have now determined the 1.95 angstrom resolution crystal structure of recombinant human apoM expressed in Escherichia coli and made the unexpected discovery that apoM, although refolded from inclusion bodies, was in complex with fatty acids containing 14, 16 or 18 carbon atoms. ApoM displays the typical lipocalin fold characterised by an eight-stranded antiparallel beta-barrel that encloses an internal ligand-binding pocket. The crystal structures of two different complexes provide a detailed picture of the ligand-binding determinants of apoM. Additional fatty acid- and lipid-binding studies with apoM and the mutants apoM(W47F) and apoM(W100F) showed that sphingosine-1-phosphate is able to displace the bound fatty acids and efficiently quenched the intrinsic fluorescence with an IC50 of 0.90 mu M. Whereas the fatty acids bound in the crystal structure could be a mere consequence of recombinant protein production, the observed binding of sphingosine-l-phosphate might provide a key to a better understanding of the physiological function of apoM. (C) 2009 Elsevier Ltd. All rights reserved.
Department/s
Publishing year
2009
Language
English
Pages
920-936
Publication/Series
Journal of Molecular Biology
Volume
393
Issue
4
Document type
Journal article
Publisher
Elsevier
Topic
- Medicinal Chemistry
Keywords
- lipocalin
- binding
- fatty acid
- ligand-binding specificity
- lipoproteins
- crystal structure
Status
Published
Research group
- Clinical Chemistry, Malmö
ISBN/ISSN/Other
- ISSN: 1089-8638