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Is apolipoprotein D a mammalian bilin-binding protein?
1Laboratory of Mathematical Biology, National Cancer Institute, Frederick, MD 21701.
The New Biologist
|February 1, 1990
Summary
Human apolipoprotein D (APO-D), a serum glycoprotein, may bind heme-related compounds like bilirubin. This suggests a novel biological role for APO-D, distinct from its previously understood functions.
Area of Science:
- Biochemistry
- Molecular Biology
- Structural Biology
Background:
- Human apolipoprotein D (APO-D) is a serum glycoprotein.
- APO-D belongs to the alpha 2-microglobulin superfamily, known for transporting hydrophobic ligands.
- Its specific ligand binding and biological role remain unclear.
Purpose of the Study:
- To investigate the ligand specificity of human apolipoprotein D (APO-D).
- To explore potential biological roles of APO-D congruent with its evolutionary history and tissue distribution.
Main Methods:
- Comparative analysis of APO-D with superfamily members.
- Construction of a detailed molecular model of APO-D using homology with insecticyanin.
- Analysis of the APO-D binding pocket geometry and side chain topology.
- Preliminary binding experiments with purified APO-D.
Main Results:
- Molecular modeling suggests heme-related compounds are favorable ligands for APO-D.
- APO-D exhibits a one-to-one molar ratio binding with bilirubin.
- These findings contrast with potential binding of cholesterol or cholesteryl ester.
Conclusions:
- Human apolipoprotein D (APO-D) likely binds heme-related compounds, such as bilirubin.
- This identifies a potential new biological function for APO-D.
- The proposed role aligns better with APO-D's known tissue distribution and evolutionary background.